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Author	Title	Year	Journal/Proceedings	Reftype	DOI/URL
Chang, R.Y.W., Miller, C.E., Dinardo, S.J., Karion, A., Sweeney, C., Daube, B.C., Henderson, J.M., Mountain, M.E., Eluszkiewicz, J., Miller, J.B., Bruhwiler, L.M.P. and Wofsy, S.C.	Methane emissions from Alaska in 2012 from CARVE airborne observations [Abstract] [BibTeX]	2014	PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Vol. 111(47), pp. 16694-16699	article	DOI
Abstract: We determined methane (CH4) emissions from Alaska using airborne measurements from the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Atmospheric sampling was conducted between May and September 2012 and analyzed using a customized version of the polar weather research and forecast model linked to a Lagrangian particle dispersion model (stochastic time-inverted Lagrangian transport model). We estimated growing season CH4 fluxes of 8 +/- 2 mg CH4.m(-2).d(-1) averaged over all of Alaska, corresponding to fluxes from wetlands of 56(-13)(+22) mg CH4.m(-2).d(-1) if we assumed that wetlands are the only source from the land surface (all uncertainties are 95% confidence intervals from a bootstrapping analysis). Fluxes roughly doubled from May to July, then decreased gradually in August and September. Integrated emissions totaled 2.1 +/- 0.5 Tg CH4 for Alaska from May to September 2012, close to the average (2.3; a range of 0.7 to 6 Tg CH4) predicted by various land surface models and inversion analyses for the growing season. Methane emissions from boreal Alaska were larger than from the North Slope; the monthly regional flux estimates showed no evidence of enhanced emissions during early spring or late fall, although these bursts may be more localized in time and space than can be detected by our analysis. These results provide an important baseline to which future studies can be compared.
BibTeX: @article{WOS:000345662700026, author = {Chang, Rachel Y. -W. and Miller, Charles E. and Dinardo, Steven J. and Karion, Anna and Sweeney, Colm and Daube, Bruce C. and Henderson, John M. and Mountain, Marikate E. and Eluszkiewicz, Janusz and Miller, John B. and Bruhwiler, Lori M. P. and Wofsy, Steven C.}, title = {Methane emissions from Alaska in 2012 from CARVE airborne observations}, journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, year = {2014}, volume = {111}, number = {47}, pages = {16694-16699}, doi = {https://doi.org/10.1073/pnas.1412953111} }
Feldman, D.R., Collins, W.D., Gero, P.J., Torn, M.S., Mlawer, E.J. and Shippert, T.R.	Observational determination of surface radiative forcing by CO2 from 2000 to 2010 [Abstract] [BibTeX]	2015	NATURE Vol. 519(7543), pp. 339+	article	DOI
Abstract: The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing', calculated as the difference between estimates of the Earth's radiation field from pre-industrial and presentday concentrations of these gases. Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annualmean radiative forcing at the tropopause of 1.82 +/- 0.19W m(-2) (ref. 2). However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO2. Here we present observationally based evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO2. The time series of this forcing at the two locations the Southern Great Plains and the North Slope of Alaska are derived from Atmospheric Emitted Radiance Interferometer spectra' together with ancillary measurements and thoroughly corroborated radiative transfer calculations'. The time series both show statistically significant trends of 0.2 W m(-2) per decade (with respective uncertainties of +/- 0.06 W m(-2) per decade and 0.07 W m(-2) per decade) and have seasonal ranges of 0.1-0.2W m(-2). This is approximately ten per cent of the trend in downwelling longwave radiation'''. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.
BibTeX: @article{WOS:000351171900038, author = {Feldman, D. R. and Collins, W. D. and Gero, P. J. and Torn, M. S. and Mlawer, E. J. and Shippert, T. R.}, title = {Observational determination of surface radiative forcing by CO2 from 2000 to 2010}, journal = {NATURE}, year = {2015}, volume = {519}, number = {7543}, pages = {339+}, doi = {https://doi.org/10.1038/nature14240} }
von Schneidemesser, E., Monks, P.S., Allan, J.D., Bruhwiler, L., Forster, P., Fowler, D., Lauer, A., Morgan, W.T., Paasonen, P., Righi, M., Sindelarova, K. and Sutton, M.A.	Chemistry and the Linkages between Air Quality and Climate Change [BibTeX]	2015	CHEMICAL REVIEWS Vol. 115(10), pp. 3856-3897	article	DOI
BibTeX: @article{WOS:000355383900006, author = {von Schneidemesser, Erika and Monks, Paul S. and Allan, James D. and Bruhwiler, Lori and Forster, Piers and Fowler, David and Lauer, Axel and Morgan, William T. and Paasonen, Pauli and Righi, Mattia and Sindelarova, Katerina and Sutton, Mark A.}, title = {Chemistry and the Linkages between Air Quality and Climate Change}, journal = {CHEMICAL REVIEWS}, year = {2015}, volume = {115}, number = {10}, pages = {3856-3897}, doi = {https://doi.org/10.1021/acs.chemrev.5b00089} }
Turner, A.J., Jacob, D.J., Wecht, K.J., Maasakkers, J.D., Lundgren, E., Andrews, A.E., Biraud, S.C., Boesch, H., Bowman, K.W., Deutscher, N.M., Dubey, M.K., Griffith, D.W.T., Hase, F., Kuze, A., Notholt, J., Ohyama, H., Parker, R., Payne, V.H., Sussmann, R., Sweeney, C., Velazco, V.A., Warneke, T., Wennberg, P.O. and Wunch, D.	Estimating global and North American methane emissions with high spatial resolution using GOSAT satellite data [Abstract] [BibTeX]	2015	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 15(12), pp. 7049-7069	article	DOI
Abstract: We use 2009-2011 space-borne methane observations from the Greenhouse Gases Observing SATellite (GOSAT) to estimate global and North American methane emissions with 4A degrees x 5A degrees and up to 50 km x 50 km spatial resolution, respectively. GEOS-Chem and GOSAT data are first evaluated with atmospheric methane observations from surface and tower networks (NOAA/ESRL, TCCON) and aircraft (NOAA/ESRL, HIPPO), using the GEOS-Chem chemical transport model as a platform to facilitate comparison of GOSAT with in situ data. This identifies a high-latitude bias between the GOSAT data and GEOS-Chem that we correct via quadratic regression. Our global adjoint-based inversion yields a total methane source of 539 Tg a(-1) with some important regional corrections to the EDGARv4.2 inventory used as a prior. Results serve as dynamic boundary conditions for an analytical inversion of North American methane emissions using radial basis functions to achieve high resolution of large sources and provide error characterization. We infer a US anthropogenic methane source of 40.2-42.7 Tg a(-1), as compared to 24.9-27.0 Tg a(-1) in the EDGAR and EPA bottom-up inventories, and 30.0-44.5 Tg a(-1) in recent inverse studies. Our estimate is supported by independent surface and aircraft data and by previous inverse studies for California. We find that the emissions are highest in the southern-central US, the Central Valley of California, and Florida wetlands; large isolated point sources such as the US Four Corners also contribute. Using prior information on source locations, we attribute 29-44 % of US anthropogenic methane emissions to livestock, 22-31 % to oil/gas, 20 % to landfills/wastewater, and 11-15 % to coal. Wetlands contribute an additional 9.0-10.1 Tg a(-1).
BibTeX: @article{WOS:000357117500034, author = {Turner, A. J. and Jacob, D. J. and Wecht, K. J. and Maasakkers, J. D. and Lundgren, E. and Andrews, A. E. and Biraud, S. C. and Boesch, H. and Bowman, K. W. and Deutscher, N. M. and Dubey, M. K. and Griffith, D. W. T. and Hase, F. and Kuze, A. and Notholt, J. and Ohyama, H. and Parker, R. and Payne, V. H. and Sussmann, R. and Sweeney, C. and Velazco, V. A. and Warneke, T. and Wennberg, P. O. and Wunch, D.}, title = {Estimating global and North American methane emissions with high spatial resolution using GOSAT satellite data}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2015}, volume = {15}, number = {12}, pages = {7049-7069}, doi = {https://doi.org/10.5194/acp-15-7049-2015} }
Parmentier, F.-J.W., Zhang, W., Mi, Y., Zhu, X., van Huissteden, J., Hayes, D.J., Zhuang, Q., Christensen, T.R. and McGuire, A.D.	Rising methane emissions from northern wetlands associated with sea ice decline [Abstract] [BibTeX]	2015	GEOPHYSICAL RESEARCH LETTERS Vol. 42(17), pp. 7214-7222	article	DOI
Abstract: The Arctic is rapidly transitioning toward a seasonal sea ice-free state, perhaps one of the most apparent examples of climate change in the world. This dramatic change has numerous consequences, including a large increase in air temperatures, which in turn may affect terrestrial methane emissions. Nonetheless, terrestrial and marine environments are seldom jointly analyzed. By comparing satellite observations of Arctic sea ice concentrations to methane emissions simulated by three process-based biogeochemical models, this study shows that rising wetland methane emissions are associated with sea ice retreat. Our analyses indicate that simulated high-latitude emissions for 2005-2010 were, on average, 1.7 Tg CH4 yr(-1) higher compared to 1981-1990 due to a sea ice-induced, autumn-focused, warming. Since these results suggest a continued rise in methane emissions with future sea ice decline, observation programs need to include measurements during the autumn to further investigate the impact of this spatial connection on terrestrial methane emissions.
BibTeX: @article{WOS:000363411200044, author = {Parmentier, Frans-Jan W. and Zhang, Wenxin and Mi, Yanjiao and Zhu, Xudong and van Huissteden, Jacobus and Hayes, Daniel J. and Zhuang, Qianlai and Christensen, Torben R. and McGuire, A. David}, title = {Rising methane emissions from northern wetlands associated with sea ice decline}, journal = {GEOPHYSICAL RESEARCH LETTERS}, year = {2015}, volume = {42}, number = {17}, pages = {7214-7222}, doi = {https://doi.org/10.1002/2015GL065013} }
Zona, D., Gioli, B., Commane, R., Lindaas, J., Wofsy, S.C., Miller, C.E., Dinardo, S.J., Dengel, S., Sweeney, C., Karion, A., Chang, R.Y.W., Henderson, J.M., Murphy, P.C., Goodrich, J.P., Moreaux, V., Liljedahl, A., Watts, J.D., Kimball, J.S., Lipson, D.A. and Oechel, W.C.	Cold season emissions dominate the Arctic tundra methane budget [Abstract] [BibTeX]	2016	PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Vol. 113(1), pp. 40-45	article	DOI
Abstract: Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for >= 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the ``zero curtain'' period, when subsurface soil temperatures are poised near 0 degrees C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 +/- 5 (95% confidence interval) Tg CH4 y(-1), similar to 25% of global emissions from extratropical wetlands, or similar to 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.
BibTeX: @article{WOS:000367520400029, author = {Zona, Donatella and Gioli, Beniamino and Commane, Roisin and Lindaas, Jakob and Wofsy, Steven C. and Miller, Charles E. and Dinardo, Steven J. and Dengel, Sigrid and Sweeney, Colm and Karion, Anna and Chang, Rachel Y. -W. and Henderson, John M. and Murphy, Patrick C. and Goodrich, Jordan P. and Moreaux, Virginie and Liljedahl, Anna and Watts, Jennifer D. and Kimball, John S. and Lipson, David A. and Oechel, Walter C.}, title = {Cold season emissions dominate the Arctic tundra methane budget}, journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, year = {2016}, volume = {113}, number = {1}, pages = {40-45}, doi = {https://doi.org/10.1073/pnas.1516017113} }
Wik, M., Varner, R.K., Anthony, K.W., MacIntyre, S. and Bastviken, D.	Climate-sensitive northern lakes and ponds are critical components of methane release [Abstract] [BibTeX]	2016	NATURE GEOSCIENCE Vol. 9(2), pp. 99+	article	DOI
Abstract: Lakes and ponds represent one of the largest natural sources of the greenhouse gas methane. By surface area, almost half of these waters are located in the boreal region and northwards. A synthesis of measurements of methane emissions from 733 lakes and ponds north of similar to 50 degrees N, combined with new inventories of inland waters, reveals that emissions from these high latitudes amount to around 16.5 Tg CH4 yr(-1) (12.4 Tg CH4-C yr(-1)). This estimate - from lakes and ponds alone - is equivalent to roughly two-thirds of the inverse model calculation of all natural methane sources in the region. Thermokarst water bodies have received attention for their high emission rates, but we find that post-glacial lakes are a larger regional source due to their larger areal extent. Water body depth, sediment type and ecoclimatic region are also important in explaining variation in methane fluxes. Depending on whether warming and permafrost thaw cause expansion or contraction of lake and pond areal coverage, we estimate that annual water body emissions will increase by 20-54% before the end of the century if ice-free seasons are extended by 20 days. We conclude that lakes and ponds are a dominant methane source at high northern latitudes.
BibTeX: @article{WOS:000369324600010, author = {Wik, Martin and Varner, Ruth K. and Anthony, Katey Walter and MacIntyre, Sally and Bastviken, David}, title = {Climate-sensitive northern lakes and ponds are critical components of methane release}, journal = {NATURE GEOSCIENCE}, year = {2016}, volume = {9}, number = {2}, pages = {99+}, doi = {https://doi.org/10.1038/NGEO2578} }
Tian, H., Lu, C., Ciais, P., Michalak, A.M., Canadell, J.G., Saikawa, E., Huntzinger, D.N., Gurney, K.R., Sitch, S., Zhang, B., Yang, J., Bousquet, P., Bruhwiler, L., Chen, G., Dlugokencky, E., Friedlingstein, P., Melillo, J., Pan, S., Poulter, B., Prinn, R., Saunois, M., Schwalm, C.R. and Wofsy, S.C.	The terrestrial biosphere as a net source of greenhouse gases to the atmosphere [Abstract] [BibTeX]	2016	NATURE Vol. 531(7593), pp. 225+	article	DOI
Abstract: The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and therefore has an important role in regulating atmospheric composition and climate1. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change(2,3). The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively(4-6), but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO2 equivalent per year) of 3.9 +/- 3.8 (top down) and 5.4 +/- 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.
BibTeX: @article{WOS:000371665100039, author = {Tian, Hanqin and Lu, Chaoqun and Ciais, Philippe and Michalak, Anna M. and Canadell, Josep G. and Saikawa, Eri and Huntzinger, Deborah N. and Gurney, Kevin R. and Sitch, Stephen and Zhang, Bowen and Yang, Jia and Bousquet, Philippe and Bruhwiler, Lori and Chen, Guangsheng and Dlugokencky, Edward and Friedlingstein, Pierre and Melillo, Jerry and Pan, Shufen and Poulter, Benjamin and Prinn, Ronald and Saunois, Marielle and Schwalm, Christopher R. and Wofsy, Steven C.}, title = {The terrestrial biosphere as a net source of greenhouse gases to the atmosphere}, journal = {NATURE}, year = {2016}, volume = {531}, number = {7593}, pages = {225+}, doi = {https://doi.org/10.1038/nature16946} }
Miller, S.M., Commane, R., Melton, J.R., Andrews, A.E., Benmergui, J., Dlugokencky, E.J., Janssens-Maenhout, G., Michalak, A.M., Sweeney, C. and Worthy, D.E.J.	Evaluation of wetland methane emissions across North America using atmospheric data and inverse modeling [Abstract] [BibTeX]	2016	BIOGEOSCIENCES Vol. 13(4), pp. 1329-1339	article	DOI
Abstract: Existing estimates of methane (CH4) fluxes from North American wetlands vary widely in both magnitude and distribution. In light of these differences, this study uses atmospheric CH4 observations from the US and Canada to analyze seven different bottom-up, wetland CH4 estimates reported in a recent model comparison project. We first use synthetic data to explore whether wetland CH4 fluxes are detectable at atmospheric observation sites. We find that the observation network can detect aggregate wetland fluxes from both eastern and western Canada but generally not from the US. Based upon these results, we then use real data and inverse modeling results to analyze the magnitude, seasonality, and spatial distribution of each model estimate. The magnitude of Canadian fluxes in many models is larger than indicated by atmospheric observations. Many models predict a seasonality that is narrower than implied by inverse modeling results, possibly indicating an oversensitivity to air or soil temperatures. The LPJ-Bern and SDGVM models have a geographic distribution that is most consistent with atmospheric observations, depending upon the region and season. These models utilize land cover maps or dynamic modeling to estimate wetland coverage while most other models rely primarily on remote sensing inundation data.
BibTeX: @article{WOS:000372082200030, author = {Miller, Scot M. and Commane, Roisin and Melton, Joe R. and Andrews, Arlyn E. and Benmergui, Joshua and Dlugokencky, Edward J. and Janssens-Maenhout, Greet and Michalak, Anna M. and Sweeney, Colm and Worthy, Doug E. J.}, title = {Evaluation of wetland methane emissions across North America using atmospheric data and inverse modeling}, journal = {BIOGEOSCIENCES}, year = {2016}, volume = {13}, number = {4}, pages = {1329-1339}, doi = {https://doi.org/10.5194/bg-13-1329-2016} }
Turner, A.J., Jacob, D.J., Benmergui, J., Wofsy, S.C., Maasakkers, J.D., Butz, A., Hasekamp, O. and Biraud, S.C.	A large increase in US methane emissions over the past decade inferred from satellite data and surface observations [Abstract] [BibTeX]	2016	GEOPHYSICAL RESEARCH LETTERS Vol. 43(5), pp. 2218-2224	article	DOI
Abstract: The global burden of atmospheric methane has been increasing over the past decade, but the causes are not well understood. National inventory estimates from the U.S. Environmental Protection Agency indicate no significant trend in U.S. anthropogenic methane emissions from 2002 to present. Here we use satellite retrievals and surface observations of atmospheric methane to suggest that U.S. methane emissions have increased by more than 30% over the 2002-2014 period. The trend is largest in the central part of the country, but we cannot readily attribute it to any specific source type. This large increase in U.S. methane emissions could account for 30-60% of the global growth of atmospheric methane seen in the past decade.
BibTeX: @article{WOS:000373109800053, author = {Turner, A. J. and Jacob, D. J. and Benmergui, J. and Wofsy, S. C. and Maasakkers, J. D. and Butz, A. and Hasekamp, O. and Biraud, S. C.}, title = {A large increase in US methane emissions over the past decade inferred from satellite data and surface observations}, journal = {GEOPHYSICAL RESEARCH LETTERS}, year = {2016}, volume = {43}, number = {5}, pages = {2218-2224}, doi = {https://doi.org/10.1002/2016GL067987} }
Dalsoren, S.B., Myhre, C.L., Myhre, G., Gomez-Pelaez, A.J., Sovde, O.A., Isaksen, I.S.A., Weiss, R.F. and Harth, C.M.	Atmospheric methane evolution the last 40 years [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(5), pp. 3099-3126	article	DOI
Abstract: Observations at surface sites show an increase in global mean surface methane (CH4) of about 180 parts per billion (ppb) (above 10 %) over the period 1984-2012. Over this period there are large fluctuations in the annual growth rate. In this work, we investigate the atmospheric CH4 evolution over the period 1970-2012 with the Oslo CTM3 global chemical transport model (CTM) in a bottom-up approach. We thoroughly assess data from surface measurement sites in international networks and select a subset suited for comparisons with the output from the CTM. We compare model results and observations to understand causes for both long-term trends and short-term variations. Employing Oslo CTM3 we are able to reproduce the seasonal and year-to-year variations and shifts between years with consecutive growth and stagnation, both at global and regional scales. The overall CH4 trend over the period is reproduced, but for some periods the model fails to reproduce the strength of the growth. The model overestimates the observed growth after 2006 in all regions. This seems to be explained by an overly strong increase in anthropogenic emissions in Asia, having global impact. Our findings confirm other studies questioning the timing or strength of the emission changes in Asia in the EDGAR v4.2 emission inventory over recent decades. The evolution of CH4 is not only controlled by changes in sources, but also by changes in the chemical loss in the atmosphere and soil uptake. The atmospheric CH4 lifetime is an indicator of the CH4 loss. In our simulations, the atmospheric CH4 lifetime decreases by more than 8 % from 1970 to 2012, a significant reduction of the residence time of this important greenhouse gas. Changes in CO and NOx emissions, specific humidity, and ozone column drive most of this, and we provide simple prognostic equations for the relations between those and the CH4 lifetime. The reduced lifetime results in substantial growth in the chemical CH4 loss (relative to its burden) and dampens the CH4 growth.
BibTeX: @article{WOS:000374702000022, author = {Dalsoren, Stig B. and Myhre, Cathrine L. and Myhre, Gunnar and Gomez-Pelaez, Angel J. and Sovde, Ole A. and Isaksen, Ivar S. A. and Weiss, Ray F. and Harth, Christina M.}, title = {Atmospheric methane evolution the last 40 years}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {5}, pages = {3099-3126}, doi = {https://doi.org/10.5194/acp-16-3099-2016} }
Hausmann, P., Sussmann, R. and Smale, D.	Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007-2014): top-down estimate from ethane and methane column observations [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(5), pp. 3227-3244	article	DOI
Abstract: Harmonized time series of column-averaged mole fractions of atmospheric methane and ethane over the period 1999-2014 are derived from solar Fourier transform infrared (FTIR) measurements at the Zugspitze summit (47A degrees aEuro-N, 11A degrees aEuro-E; 2964 m a.s.l.) and at Lauder (45A degrees aEuro-S, 170A degrees aEuro-E; 370 m a.s.l.). Long-term trend analysis reveals a consistent renewed methane increase since 2007 of 6.2 [5.6, 6.9] ppb yr(-1) (parts-per-billion per year) at the Zugspitze and 6.0 [5.3, 6.7] ppb yr(-1) at Lauder (95 % confidence intervals). Several recent studies provide pieces of evidence that the renewed methane increase is most likely driven by two main factors: (i) increased methane emissions from tropical wetlands, followed by (ii) increased thermogenic methane emissions due to growing oil and natural gas production. Here, we quantify the magnitude of the second class of sources, using long-term measurements of atmospheric ethane as a tracer for thermogenic methane emissions. In 2007, after years of weak decline, the Zugspitze ethane time series shows the sudden onset of a significant positive trend (2.3 [1.8, 2.8]x -10(-2) ppb yr(-1) for 2007-2014), while a negative trend persists at Lauder after 2007 (-0.4 [-0.6, -0.1]x -10(-2) ppb yr(-1)). Zugspitze methane and ethane time series are significantly correlated for the period 2007-2014 and can be assigned to thermogenic methane emissions with an ethane-to-methane ratio (EMR) of 12-19 %. We present optimized emission scenarios for 2007-2014 derived from an atmospheric two-box model. From our trend observations we infer a total ethane emission increase over the period 2007-2014 from oil and natural gas sources of 1-11 Tg yr(-1) along with an overall methane emission increase of 24-45 Tg yr(-1). Based on these results, the oil and natural gas emission contribution (C) to the renewed methane increase is deduced using three different emission scenarios with dedicated EMR ranges. Reference scenario 1 assumes an oil and gas emission combination with EMR= -7.0-16.2 %, which results in a minimum contribution C > -39 % (given as lower bound of 95 % confidence interval). Beside this most plausible scenario 1, we consider two less realistic limiting cases of pure oil-related emissions (scenario 2 with EMR= -16.2-31.4 %) and pure natural gas sources (scenario 3 with EMR= -4.4-7.0- %), which result in C > -18 % and C > -73 %, respectively. Our results suggest that long-term observations of column-averaged ethane provide a valuable constraint on the source attribution of methane emission changes and provide basic knowledge for developing effective climate change mitigation strategies.
BibTeX: @article{WOS:000374702000029, author = {Hausmann, Petra and Sussmann, Ralf and Smale, Dan}, title = {Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007-2014): top-down estimate from ethane and methane column observations}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {5}, pages = {3227-3244}, doi = {https://doi.org/10.5194/acp-16-3227-2016} }
Pandey, S., Houweling, S., Krol, M., Aben, I., Chevallier, F., Dlugokencky, E.J., Gatti, L.V., Gloor, E., Miller, J.B., Detmers, R., Machida, T. and Rockmann, T.	Inverse modeling of GOSAT-retrieved ratios of total column CH4 and CO2 for 2009 and 2010 [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(8), pp. 5043-5062	article	DOI
Abstract: This study investigates the constraint provided by greenhouse gas measurements from space on surface fluxes. Imperfect knowledge of the light path through the atmosphere, arising from scattering by clouds and aerosols, can create biases in column measurements retrieved from space. To minimize the impact of such biases, ratios of total column retrieved CH4 and CO2 (X-ratio) have been used. We apply the ratio inversion method described in Pandey et al. (2015) to retrievals from the Greenhouse Gases Observing SATellite (GOSAT). The ratio inversion method uses the measured X-ratio as a weak constraint on CO2 fluxes. In contrast, the more common approach of inverting proxy CH4 retrievals (Frankenberg et al., 2005) prescribes atmospheric CO2 fields and optimizes only CH4 fluxes. The TM5-4DVAR (Tracer Transport Model version 5-variational data assimilation system) inverse modeling system is used to simultaneously optimize the fluxes of CH4 and CO2 for 2009 and 2010. The results are compared to proxy inversions using model-derived CO2 mixing ratios (XCO2model) from CarbonTracker and the Monitoring Atmospheric Composition and Climate (MACC) Reanalysis CO2 product. The performance of the inverse models is evaluated using measurements from three aircraft measurement projects. X-ratio and XCO2model are compared with TCCON retrievals to quantify the relative importance of errors in these components of the proxy XCH4 retrieval (XCH4proxy). We find that the retrieval errors in X-ratio (meanaEuro- = aEuro-0.61aEuro-%) are generally larger than the errors in XCO2model (meanaEuro- = aEuro-0.24 and 0.01aEuro-% for CarbonTracker and MACC, respectively). On the annual timescale, the CH4 fluxes from the different satellite inversions are generally in agreement with each other, suggesting that errors in XCO2model do not limit the overall accuracy of the CH4 flux estimates. On the seasonal timescale, however, larger differences are found due to uncertainties in XCO2model, particularly over Australia and in the tropics. The ratio method stays closer to the a priori CH4 flux in these regions, because it is capable of simultaneously adjusting the CO2 fluxes. Over tropical South America, comparison to independent measurements shows that CO2 fields derived from the ratio method are less realistic than those used in the proxy method. However, the CH4 fluxes are more realistic, because the impact of unaccounted systematic uncertainties is more evenly distributed between CO2 and CH4. The ratio inversion estimates an enhanced CO2 release from tropical South America during the dry season of 2010, which is in accordance with the findings of Gatti et al. (2014) and Van der Laan et al. (2015). The performance of the ratio method is encouraging, because despite the added nonlinearity due to the assimilation of X-ratio and the significant increase in the degree of freedom by optimizing CO2 fluxes, still consistent results are obtained with respect to other CH4 inversions..
BibTeX: @article{WOS:000376937000018, author = {Pandey, Sudhanshu and Houweling, Sander and Krol, Maarten and Aben, Ilse and Chevallier, Frederic and Dlugokencky, Edward J. and Gatti, Luciana V. and Gloor, Emanuel and Miller, John B. and Detmers, Rob and Machida, Toshinobu and Rockmann, Thomas}, title = {Inverse modeling of GOSAT-retrieved ratios of total column CH4 and CO2 for 2009 and 2010}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {8}, pages = {5043-5062}, doi = {https://doi.org/10.5194/acp-16-5043-2016} }
Karion, A., Sweeney, C., Miller, J.B., Andrews, A.E., Commane, R., Dinardo, S., Henderson, J.M., Lindaas, J., Lin, J.C., Luus, K.A., Newberger, T., Tans, P., Wofsy, S.C., Wolter, S. and Miller, C.E.	Investigating Alaskan methane and carbon dioxide fluxes using measurements from the CARVE tower [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(8), pp. 5383-5398	article	DOI
Abstract: Northern high-latitude carbon sources and sinks, including those resulting from degrading permafrost, are thought to be sensitive to the rapidly warming climate. Because the near-surface atmosphere integrates surface fluxes over large ( aEuro-500-1000aEuro-km) scales, atmospheric monitoring of carbon dioxide (CO2) and methane (CH4) mole fractions in the daytime mixed layer is a promising method for detecting change in the carbon cycle throughout boreal Alaska. Here we use CO2 and CH4 measurements from a NOAA tower 17aEuro-km north of Fairbanks, AK, established as part of NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE), to investigate regional fluxes of CO2 and CH4 for 2012-2014. CARVE was designed to use aircraft and surface observations to better understand and quantify the sensitivity of Alaskan carbon fluxes to climate variability. We use high-resolution meteorological fields from the Polar Weather Research and Forecasting (WRF) model coupled with the Stochastic Time-Inverted Lagrangian Transport model (hereafter, WRF-STILT), along with the Polar Vegetation Photosynthesis and Respiration Model (PolarVPRM), to investigate fluxes of CO2 in boreal Alaska using the tower observations, which are sensitive to large areas of central Alaska. We show that simulated PolarVPRM-WRF-STILT CO2 mole fractions show remarkably good agreement with tower observations, suggesting that the WRF-STILT model represents the meteorology of the region quite well, and that the PolarVPRM flux magnitudes and spatial distribution are generally consistent with CO2 mole fractions observed at the CARVE tower. One exception to this good agreement is that during the fall of all 3 years, PolarVPRM cannot reproduce the observed CO2 respiration. Using the WRF-STILT model, we find that average CH4 fluxes in boreal Alaska are somewhat lower than flux estimates by Chang et al. (2014) over all of Alaska for May-September 2012; we also find that enhancements appear to persist during some wintertime periods, augmenting those observed during the summer and fall. The possibility of significant fall and winter CO2 and CH4 fluxes underscores the need for year-round in situ observations to quantify changes in boreal Alaskan annual carbon balance.
BibTeX: @article{WOS:000376937000037, author = {Karion, Anna and Sweeney, Colm and Miller, John B. and Andrews, Arlyn E. and Commane, Roisin and Dinardo, Steven and Henderson, John M. and Lindaas, Jacob and Lin, John C. and Luus, Kristina A. and Newberger, Tim and Tans, Pieter and Wofsy, Steven C. and Wolter, Sonja and Miller, Charles E.}, title = {Investigating Alaskan methane and carbon dioxide fluxes using measurements from the CARVE tower}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {8}, pages = {5383-5398}, doi = {https://doi.org/10.5194/acp-16-5383-2016} }
Liu, M., Lei, L., Liu, D. and Zeng, Z.-C.	Geostatistical Analysis of CH4 Columns over Monsoon Asia Using Five Years of GOSAT Observations [Abstract] [BibTeX]	2016	REMOTE SENSING Vol. 8(5)	article	DOI
Abstract: The aim of this study is to evaluate the Greenhouse gases Observation SATellite (GOSAT) column-averaged CH4 dry air mole fraction (XCH4) data by using geostatistical analysis and conducting comparisons with model simulations and surface emissions. Firstly, we propose the use of a data-driven mapping approach based on spatio-temporal geostatistics to generate a regular and gridded mapping dataset of XCH4 over Monsoon Asia using five years of XCH4 retrievals by GOSAT from June 2009 to May 2014. The prediction accuracy of the mapping approach is assessed by using cross-validation, which results in a significantly high correlation of 0.91 and a small mean absolute prediction error of 8.77 ppb between the observed dataset and the prediction dataset. Secondly, with the mapping data, we investigate the spatial and temporal variations of XCH4 over Monsoon Asia and compare the results with previous studies on ground and other satellite observations. Thirdly, we compare the mapping XCH4 with model simulations from CarbonTracker-CH4 and find their spatial patterns very consistent, but GOSAT observations are more able to capture the local variability of XCH4. Finally, by correlating the mapping data with surface emission inventory, we find the geographical distribution of high CH4 values correspond well with strong emissions as indicated in the inventory map. Over the five-year period, the two datasets show a significant high correlation coefficient (0.80), indicating the dominant role of surface emissions in determining the distribution of XCH4 concentration in this region and suggesting a promising statistical way of constraining surface CH4 sources and sinks, which is simple and easy to implement using satellite observations over a long term period.
BibTeX: @article{WOS:000378406400005, author = {Liu, Min and Lei, Liping and Liu, Da and Zeng, Zhao-Cheng}, title = {Geostatistical Analysis of CH4 Columns over Monsoon Asia Using Five Years of GOSAT Observations}, journal = {REMOTE SENSING}, year = {2016}, volume = {8}, number = {5}, doi = {https://doi.org/10.3390/rs8050361} }
Uttal, T., Starkweather, S., Drummond, J.R., Vihma, T., Makshtas, A.P., Darby, L.S., Burkhart, J.F., Cox, C.J., Schmeisser, L.N., Haiden, T., Maturilli, M., Shupe, M.D., De Boer, G., Saha, A., Grachev, A.A., Crepinsek, S.M., Bruhwiler, L., Goodison, B., McArthur, B., Walden, V.P., Dlugokencky, E.J., Persson, P.O.G., Lesins, G., Laurila, T., Ogren, J.A., Stone, R., Long, C.N., Sharma, S., Massling, A., Turner, D.D., Stanitski, D.M., Asmi, E., Aurela, M., Skov, H., Eleftheriadis, K., Virkkula, A., Platt, A., Forland, E.J., Iijima, Y., Nielsen, I.E., Bergin, M.H., Candlish, L., Zimov, N.S., Zimov, S.A., O'Neill, N.T., Fogal, P.F., Kivi, R., Konopleva-Akish, E.A., Verlinde, J., Kustov, V.Y., Vasel, B., Ivakhov, V.M., Viisanen, Y. and Intrieri, J.M.	International Arctic Systems for Observing the Atmosphere: An International Polar Year Legacy Consortium [Abstract] [BibTeX]	2016	BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY Vol. 97(6), pp. 1033-1056	article	DOI
Abstract: International Arctic Systems for Observing the Atmosphere (IASOA) activities and partnerships were initiated as a part of the 2007-09 International Polar Year (IPY) and are expected to continue for many decades as a legacy program. The IASOA focus is on coordinating intensive measurements of the Arctic atmosphere collected in the United States, Canada, Russia, Norway, Finland, and Greenland to create synthesis science that leads to an understanding of why and not just how the Arctic atmosphere is evolving. The IASOA premise is that there are limitations with Arctic modeling and satellite observations that can only be addressed with boots-on-the-ground, in situ observations and that the potential of combining individual station and network measurements into an integrated observing system is tremendous. The IASOA vision is that by further integrating with other network observing programs focusing on hydrology, glaciology, oceanography, terrestrial, and biological systems it will be possible to understand the mechanisms of the entire Arctic system, perhaps well enough for humans to mitigate undesirable variations and adapt to inevitable change.
BibTeX: @article{WOS:000380345200013, author = {Uttal, Taneil and Starkweather, Sandra and Drummond, James R. and Vihma, Timo and Makshtas, Alexander P. and Darby, Lisa S. and Burkhart, John F. and Cox, Christopher J. and Schmeisser, Lauren N. and Haiden, Thomas and Maturilli, Marion and Shupe, Matthew D. and De Boer, Gijs and Saha, Auromeet and Grachev, Andrey A. and Crepinsek, Sara M. and Bruhwiler, Lori and Goodison, Barry and McArthur, Bruce and Walden, Von P. and Dlugokencky, Edward J. and Persson, P. Ola G. and Lesins, Glen and Laurila, Tuomas and Ogren, John A. and Stone, Robert and Long, Charles N. and Sharma, Sangeeta and Massling, Andreas and Turner, David D. and Stanitski, Diane M. and Asmi, Eija and Aurela, Mika and Skov, Henrik and Eleftheriadis, Konstantinos and Virkkula, Aki and Platt, Andrew and Forland, Eirik J. and Iijima, Yoshihiro and Nielsen, Ingeborg E. and Bergin, Michael H. and Candlish, Lauren and Zimov, Nikita S. and Zimov, Sergey A. and O'Neill, Norman T. and Fogal, Pierre F. and Kivi, Rigel and Konopleva-Akish, Elena A. and Verlinde, Johannes and Kustov, Vasily Y. and Vasel, Brian and Ivakhov, Viktor M. and Viisanen, Yrjoe and Intrieri, Janet M.}, title = {International Arctic Systems for Observing the Atmosphere: An International Polar Year Legacy Consortium}, journal = {BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY}, year = {2016}, volume = {97}, number = {6}, pages = {1033-1056}, doi = {https://doi.org/10.1175/BAMS-D-14-00145.1} }
Sweeney, C., Dlugokencky, E., Miller, C.E., Wofsy, S., Karion, A., Dinardo, S., Chang, R.Y.W., Miller, J.B., Bruhwiler, L., Crotwell, A.M., Newberger, T., McKain, K., Stone, R.S., Wolter, S.E., Lang, P.E. and Tans, P.	No significant increase in long-term CH4 emissions on North Slope of Alaska despite significant increase in air temperature [Abstract] [BibTeX]	2016	GEOPHYSICAL RESEARCH LETTERS Vol. 43(12), pp. 6604-6611	article	DOI
Abstract: Continuous measurements of atmospheric methane (CH4) mole fractions measured by NOAA's Global Greenhouse Gas Reference Network in Barrow, AK (BRW), show strong enhancements above background values when winds come from the land sector from July to December from 1986 to 2015, indicating that emissions from arctic tundra continue through autumn and into early winter. Twenty-nine years of measurements show little change in seasonal mean land sector CH4 enhancements, despite an increase in annual mean temperatures of 1.2 +/- 0.8 degrees C/decade (2s). The record does reveal small increases in CH4 enhancements in November and December after 2010 due to increased late-season emissions. The lack of significant long-term trends suggests that more complex biogeochemical processes are counteracting the observed short-term (monthly) temperature sensitivity of 5.0 +/- 3.6 ppb CH4/degrees C. Our results suggest that even the observed short-term temperature sensitivity from the Arctic will have little impact on the global atmospheric CH4 budget in the long term if future trajectories evolve with the same temperature sensitivity.
BibTeX: @article{WOS:000380910100083, author = {Sweeney, Colm and Dlugokencky, Edward and Miller, Charles E. and Wofsy, Steven and Karion, Anna and Dinardo, Steve and Chang, Rachel Y. -W. and Miller, John B. and Bruhwiler, Lori and Crotwell, Andrew M. and Newberger, Tim and McKain, Kathryn and Stone, Robert S. and Wolter, Sonja E. and Lang, Patricia E. and Tans, Pieter}, title = {No significant increase in long-term CH4 emissions on North Slope of Alaska despite significant increase in air temperature}, journal = {GEOPHYSICAL RESEARCH LETTERS}, year = {2016}, volume = {43}, number = {12}, pages = {6604-6611}, doi = {https://doi.org/10.1002/2016GL069292} }
Rockmann, T., Eyer, S., van der Veen, C., Popa, M.E., Tuzson, B., Monteil, G., Houweling, S., Harris, E., Brunner, D., Fischer, H., Zazzeri, G., Lowry, D., Nisbet, E.G., Brand, W.A., Necki, J.M., Emmenegger, L. and Mohn, J.	In situ observations of the isotopic composition of methane at the Cabauw tall tower site [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(16), pp. 10469-10487	article	DOI
Abstract: High-precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS)-based technique for in situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands and performed in situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of (+0.25 +/- 0.04)parts per thousand for delta C-13 and (-4.3 +/- 0.4)parts per thousand for delta D. This was corrected for, yielding a combined dataset with more than 2500 measurements of both delta C-13 and delta D. The high-precision and high-temporal-resolution dataset not only reveals the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget when they are performed at multiple sites that are representative for the entire European domain.
BibTeX: @article{WOS:000383742700003, author = {Rockmann, Thomas and Eyer, Simon and van der Veen, Carina and Popa, Maria E. and Tuzson, Bela and Monteil, Guillaume and Houweling, Sander and Harris, Eliza and Brunner, Dominik and Fischer, Hubertus and Zazzeri, Giulia and Lowry, David and Nisbet, Euan G. and Brand, Willi A. and Necki, Jaroslav M. and Emmenegger, Lukas and Mohn, Joachim}, title = {In situ observations of the isotopic composition of methane at the Cabauw tall tower site}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {16}, pages = {10469-10487}, doi = {https://doi.org/10.5194/acp-16-10469-2016} }
Xu, X., Riley, W.J., Koven, C.D., Billesbach, D.P., Chang, R.Y.W., Commane, R., Euskirchen, E.S., Hartery, S., Harazono, Y., Iwata, H., McDonald, K.C., Miller, C.E., Oechel, W.C., Poulter, B., Raz-Yaseef, N., Sweeney, C., Torn, M., Wofsy, S.C., Zhang, Z. and Zona, D.	A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands [Abstract] [BibTeX]	2016	BIOGEOSCIENCES Vol. 13(17), pp. 5043-5056	article	DOI
Abstract: Wetlands are the largest global natural methane (CH4) source, and emissions between 50 and 70 degrees N latitude contribute 10-30% to this source. Predictive capability of land models for northern wetland CH4 emissions is still low due to limited site measurements, strong spatial and temporal variability in emissions, and complex hydrological and biogeochemical dynamics. To explore this issue, we compare wetland CH4 emission predictions from the Community Land Model 4.5 (CLM4.5-BGC) with siteto regional-scale observations. A comparison of the CH4 fluxes with eddy flux data highlighted needed changes to the model's estimate of aerenchyma area, which we implemented and tested. The model modification substantially reduced biases in CH4 emissions when compared with CarbonTracker CH4 predictions. CLM4.5 CH4 emission predictions agree well with growing season (May-September) CarbonTracker Alaskan regional-level CH4 predictions and sitelevel observations. However, CLM4.5 underestimated CH4 emissions in the cold season (October-April). The monthly atmospheric CH4 mole fraction enhancements due to wetland emissions are also assessed using the Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model coupled with daily emissions from CLM4.5 and compared with aircraft CH4 mole fraction measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold-season CH4 emissions by CLM4.5. The greatest uncertainties in predicting the seasonal CH4 cycle are from the wetland extent, cold-season CH4 production and CH4 transport processes. We recommend more cold-season experimental studies in high-latitude systems, which could improve the understanding and parameterization of ecosystem structure and function during this period. Predicted CH4 emissions remain uncertain, but we show here that benchmarking against observations across spatial scales can inform model structural and parameter improvements.
BibTeX: @article{WOS:000383964200001, author = {Xu, Xiyan and Riley, William J. and Koven, Charles D. and Billesbach, Dave P. and Chang, Rachel Y. -W. and Commane, Roisin and Euskirchen, Eugenie S. and Hartery, Sean and Harazono, Yoshinobu and Iwata, Hiroki and McDonald, Kyle C. and Miller, Charles E. and Oechel, Walter C. and Poulter, Benjamin and Raz-Yaseef, Naama and Sweeney, Colm and Torn, Margaret and Wofsy, Steven C. and Zhang, Zhen and Zona, Donatella}, title = {A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands}, journal = {BIOGEOSCIENCES}, year = {2016}, volume = {13}, number = {17}, pages = {5043-5056}, doi = {https://doi.org/10.5194/bg-13-5043-2016} }
Xiong, X., Han, Y., Liu, Q. and Weng, F.	Comparison of Atmospheric Methane Retrievals From AIRS and IASI [Abstract] [BibTeX]	2016	IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING Vol. 9(7, SI), pp. 3297-3303	article	DOI
Abstract: Atmospheric methane (CH4) is a standard product of the atmospheric infrared sounder (AIRS) aboard NASA's Aqua satellite, generated at the NASA Goddard Earth Sciences Data and Information Services Center (NASA/GES/DISC), and a product of the infrared atmospheric sounding interferometer (IASI) aboard METOP-A,-B, generated at National Oceanic and Atmospheric Administration's Comprehensive Large Array-data Stewardship System. In order to understand the capability of these two sensors in observing the spatial and temporal distribution of CH4, this paper compares the CH4 products from AIRS and IASI with aircraft measurements, as well as the corresponding time series in tropics and high northern latitude regions. It is found that the mean degree of freedom from AIRS is smaller than IASI by -0.049 +/- 0.152, and in their peak sensitive altitude between 350 and 650 hPa their difference (AIRS - IASI) is about 2.8 +/- 17.2 ppb. Both AIRS and IASI can capture the latitudinal gradient, but there is a large scattering in the high northern latitude regions. They agree well in observing the summer enhancement of CH4 during the Monsoon season over South Asia, and the seasonal cycles over Siberia (except for a relatively larger difference in the cold season). These results highlight that AIRS and IASI can provide valuable information to capture the spatiotemporal variation of CH4 in the mid-upper troposphere in most periods and regions, but it is needed to further improve the data quality to make a consistent product using both sensors.
BibTeX: @article{WOS:000384905500040, author = {Xiong, Xiaozhen and Han, Yong and Liu, Quanhua and Weng, Fuzhong}, title = {Comparison of Atmospheric Methane Retrievals From AIRS and IASI}, journal = {IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING}, year = {2016}, volume = {9}, number = {7, SI}, pages = {3297-3303}, doi = {https://doi.org/10.1109/JSTARS.2016.2588279} }
Tan, Z., Zhuang, Q., Henze, D.K., Frankenberg, C., Dlugokencky, E., Sweeney, C., Turner, A.J., Sasakawa, M. and Machida, T.	Inverse modeling of pan-Arctic methane emissions at high spatial resolution: what can we learn from assimilating satellite retrievals and using different process-based wetland and lake biogeochemical models? [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(19), pp. 12649-12666	article	DOI
Abstract: Understanding methane emissions from the Arctic, a fast-warming carbon reservoir, is important for projecting future changes in the global methane cycle. Here we optimized methane emissions from north of 60 degrees N (pan-Arctic) regions using a nested-grid high-resolution inverse model that assimilates both high-precision surface measurements and column-average SCanning Imaging Absorption spectroMeter for Atmospheric CHartogrphY (SCIAMACHY) satellite retrievals of methane mole fraction. For the first time, methane emissions from lakes were integrated into an atmospheric transport and inversion estimate, together with prior wetland emissions estimated with six biogeochemical models. In our estimates, in 2005, global methane emissions were in the range of 496.4-511.5 Tg yr(-1), and pan-Arctic methane emissions were in the range of 11.9-28.5 Tg yr(-1). Methane emissions from pan-Arctic wetlands and lakes were 5.5-14.2 and 2.4-14.2 Tg yr(-1), respectively. Methane emissions from Siberian wetlands and lakes are the largest and also have the largest uncertainty. Our results indicate that the uncertainty introduced by different wetland models could be much larger than the uncertainty of each inversion. We also show that assimilating satellite retrievals can reduce the un-certainty of the nested-grid inversions. The significance of lake emissions cannot be identified across the pan-Arctic by high-resolution inversions, but it is possible to identify high lake emissions from some specific regions. In contrast to global inversions, high-resolution nested-grid inversions perform better in estimating near-surface methane concentrations.
BibTeX: @article{WOS:000385403300001, author = {Tan, Zeli and Zhuang, Qianlai and Henze, Daven K. and Frankenberg, Christian and Dlugokencky, Ed and Sweeney, Colm and Turner, Alexander J. and Sasakawa, Motoki and Machida, Toshinobu}, title = {Inverse modeling of pan-Arctic methane emissions at high spatial resolution: what can we learn from assimilating satellite retrievals and using different process-based wetland and lake biogeochemical models?}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {19}, pages = {12649-12666}, doi = {https://doi.org/10.5194/acp-16-12649-2016} }
Abdalla, M., Hastings, A., Truu, J., Espenberg, M., Mander, U. and Smith, P.	Emissions of methane from northern peatlands: a review of management impacts and implications for future management options [Abstract] [BibTeX]	2016	ECOLOGY AND EVOLUTION Vol. 6(19), pp. 7080-7102	article	DOI
Abstract: Northern peatlands constitute a significant source of atmospheric methane (CH4). However, management of undisturbed peatlands, as well as the restoration of disturbed peatlands, will alter the exchange of CH4 with the atmosphere. The aim of this systematic review and meta-analysis was to collate and analyze published studies to improve our understanding of the factors that control CH4 emissions and the impacts of management on the gas flux from northern (latitude 40 degrees to 70 degrees N) peatlands. The analysis includes a total of 87 studies reporting measurements of CH4 emissions taken at 186 sites covering different countries, peatland types, and management systems. Results show that CH4 emissions from natural northern peatlands are highly variable with a 95% CI of 7.6-15.7 g C m(-2) year(-1) for the mean and 3.3-6.3 g C m(-2) year(-1) for the median. The overall annual average (mean +/- SD) is 12 +/- 21 g C m(-2) year(-1) with the highest emissions from fen ecosystems. Methane emissions from natural peatlands are mainly controlled by water table (WT) depth, plant community composition, and soil pH. Although mean annual air temperature is not a good predictor of CH4 emissions by itself, the interaction between temperature, plant community cover, WT depth, and soil pH is important. According to short-term forecasts of climate change, these complex interactions will be the main determinant of CH4 emissions from northern peatlands. Drainage significantly (p < .05) reduces CH4 emissions to the atmosphere, on average by 84%. Restoration of drained peatlands by rewetting or vegetation/rewetting increases CH4 emissions on average by 46% compared to the original premanagement CH4 fluxes. However, to fully evaluate the net effect of management practice on the greenhouse gas balance from high latitude peatlands, both net ecosystem exchange (NEE) and carbon exports need to be considered.
BibTeX: @article{WOS:000385626100029, author = {Abdalla, Mohamed and Hastings, Astley and Truu, Jaak and Espenberg, Mikk and Mander, Ulo and Smith, Pete}, title = {Emissions of methane from northern peatlands: a review of management impacts and implications for future management options}, journal = {ECOLOGY AND EVOLUTION}, year = {2016}, volume = {6}, number = {19}, pages = {7080-7102}, doi = {https://doi.org/10.1002/ece3.2469} }
Saito, M., Kim, H.-S., Ito, A., Yokota, T. and Maksyutov, S.	Enhanced Methane Emissions during Amazonian Drought by Biomass Burning [Abstract] [BibTeX]	2016	PLOS ONE Vol. 11(11)	article	DOI
Abstract: The Amazon is a significant source of atmospheric methane, but little is known about the source response to increasing drought severity and frequency. We investigated satellite observations of atmospheric column-averaged methane for the 2010 drought and subsequent 2011 wet year in the Amazon using an atmospheric inversion scheme. Our analysis indicates an increase in atmospheric methane over the southern Amazon region during the drought, representing an increase in annual emissions relative to the wet year. We attribute the increase to emissions from biomass burning driven by intense drought, combined with carbon monoxide showing seasonal variations corresponding to methane variations. We show that there is probably a strong correspondence between drought and methane emissions in the Amazon.
BibTeX: @article{WOS:000387909300032, author = {Saito, Makoto and Kim, Heon-Sook and Ito, Akihiko and Yokota, Tatsuya and Maksyutov, Shamil}, title = {Enhanced Methane Emissions during Amazonian Drought by Biomass Burning}, journal = {PLOS ONE}, year = {2016}, volume = {11}, number = {11}, doi = {https://doi.org/10.1371/journal.pone.0166039} }
Jacob, D.J., Turner, A.J., Maasakkers, J.D., Sheng, J., Sun, K., Liu, X., Chance, K., Aben, I., McKeever, J. and Frankenberg, C.	Satellite observations of atmospheric methane and their value for quantifying methane emissions [Abstract] [BibTeX]	2016	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 16(22), pp. 14371-14396	article	DOI
Abstract: Methane is a greenhouse gas emitted by a range of natural and anthropogenic sources. Atmospheric methane has been measured continuously from space since 2003, and new instruments are planned for launch in the near future that will greatly expand the capabilities of space-based observations. We review the value of current, future, and proposed satellite observations to better quantify and understand methane emissions through inverse analyses, from the global scale down to the scale of point sources and in combination with suborbital (surface and aircraft) data. Current global observations from Greenhouse Gases Observing Satellite (GOSAT) are of high quality but have sparse spatial coverage. They can quantify methane emissions on a regional scale (100-1000 km) through multiyear averaging. The Tropospheric Monitoring Instrument (TROPOMI), to be launched in 2017, is expected to quantify daily emissions on the regional scale and will also effectively detect large point sources. A different observing strategy by GHGSat (launched in June 2016) is to target limited viewing domains with very fine pixel resolution in order to detect a wide range of methane point sources. Geostationary observation of methane, still in the proposal stage, will have the unique capability of mapping source regions with high resolution, detecting transient ``super-emitter'' point sources and resolving diurnal variation of emissions from sources such as wetlands and manure. Exploiting these rapidly expanding satellite measurement capabilities to quantify methane emissions requires a parallel effort to construct high-quality spatially and sectorally resolved emission inventories. Partnership between top-down inverse analyses of atmospheric data and bottom-up construction of emission inventories is crucial to better understanding methane emission processes and subsequently informing climate policy.
BibTeX: @article{WOS:000387980100003, author = {Jacob, Daniel J. and Turner, Alexander J. and Maasakkers, Joannes D. and Sheng, Jianxiong and Sun, Kang and Liu, Xiong and Chance, Kelly and Aben, Ilse and McKeever, Jason and Frankenberg, Christian}, title = {Satellite observations of atmospheric methane and their value for quantifying methane emissions}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2016}, volume = {16}, number = {22}, pages = {14371-14396}, doi = {https://doi.org/10.5194/acp-16-14371-2016} }
Nisbet, E.G., Dlugokencky, E.J., Manning, M.R., Lowry, D., Fisher, R.E., France, J.L., Michel, S.E., Miller, J.B., White, J.W.C., Vaughn, B., Bousquet, P., Pyle, J.A., Warwick, N.J., Cain, M., Brownlow, R., Zazzeri, G., Lanoiselle, M., Manning, A.C., Gloor, E., Worthy, D.E.J., Brunke, E.-G., Labuschagne, C., Wolff, E.W. and Ganesan, A.L.	Rising atmospheric methane: 2007-2014 growth and isotopic shift [Abstract] [BibTeX]	2016	GLOBAL BIOGEOCHEMICAL CYCLES Vol. 30(9), pp. 1356-1370	article	DOI
Abstract: From 2007 to 2013, the globally averaged mole fraction of methane in the atmosphere increased by 5.7 +/- 1.2 ppb yr(-1). Simultaneously, delta C-13(CH4) (a measure of the C-13/C-12 isotope ratio in methane) has shifted to significantly more negative values since 2007. Growth was extreme in 2014, at 12.5 +/- 0.4 ppb, with a further shift to more negative values being observed at most latitudes. The isotopic evidence presented here suggests that the methane rise was dominated by significant increases in biogenic methane emissions, particularly in the tropics, for example, from expansion of tropical wetlands in years with strongly positive rainfall anomalies or emissions from increased agricultural sources such as ruminants and rice paddies. Changes in the removal rate of methane by the OH radical have not been seen in other tracers of atmospheric chemistry and do not appear to explain short-term variations in methane. Fossil fuel emissions may also have grown, but the sustained shift to more C-13-depleted values and its significant interannual variability, and the tropical and Southern Hemisphere loci of post-2007 growth, both indicate that fossil fuel emissions have not been the dominant factor driving the increase. A major cause of increased tropical wetland and tropical agricultural methane emissions, the likely major contributors to growth, may be their responses to meteorological change.
BibTeX: @article{WOS:000388457700009, author = {Nisbet, E. G. and Dlugokencky, E. J. and Manning, M. R. and Lowry, D. and Fisher, R. E. and France, J. L. and Michel, S. E. and Miller, J. B. and White, J. W. C. and Vaughn, B. and Bousquet, P. and Pyle, J. A. and Warwick, N. J. and Cain, M. and Brownlow, R. and Zazzeri, G. and Lanoiselle, M. and Manning, A. C. and Gloor, E. and Worthy, D. E. J. and Brunke, E-G. and Labuschagne, C. and Wolff, E. W. and Ganesan, A. L.}, title = {Rising atmospheric methane: 2007-2014 growth and isotopic shift}, journal = {GLOBAL BIOGEOCHEMICAL CYCLES}, year = {2016}, volume = {30}, number = {9}, pages = {1356-1370}, doi = {https://doi.org/10.1002/2016GB005406} }
Miller, S.M., Miller, C.E., Commane, R., Chang, R.Y.-W., Dinardo, S.J., Henderson, J.M., Karion, A., Lindaas, J., Melton, J.R., Miller, J.B., Sweeney, C., Wofsy, S.C. and Michalak, A.M.	A multiyear estimate of methane fluxes in Alaska from CARVE atmospheric observations [Abstract] [BibTeX]	2016	GLOBAL BIOGEOCHEMICAL CYCLES Vol. 30(10), pp. 1441-1453	article	DOI
Abstract: Methane (CH4) fluxes from Alaska and other arctic regions may be sensitive to thawing permafrost and future climate change, but estimates of both current and future fluxes from the region are uncertain. This study estimates CH4 fluxes across Alaska for 2012-2014 using aircraft observations from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) and a geostatistical inverse model (GIM). We find that a simple flux model based on a daily soil temperature map and a static map of wetland extent reproduces the atmospheric CH4 observations at the statewide, multiyear scale more effectively than global-scale process-based models. This result points to a simple and effective way of representing CH4 fluxes across Alaska. It further suggests that process-based models can improve their representation of key processes and that more complex processes included in these models cannot be evaluated given the information content of available atmospheric CH4 observations. In addition, we find that CH4 emissions from the North Slope of Alaska account for 24% of the total statewide flux of 1.74 +/- 0.26 Tg CH4 (for May-October). Global-scale process models only attribute an average of 3% of the total flux to this region. This mismatch occurs for two reasons: process models likely underestimate wetland extent in regions without visible surface water, and these models prematurely shut down CH4 fluxes at soil temperatures near 0 degrees C. Lastly, we find that the seasonality of CH4 fluxes varied during 2012-2014 but that total emissions did not differ significantly among years, despite substantial differences in soil temperature and precipitation.
BibTeX: @article{WOS:000388458000004, author = {Miller, Scot M. and Miller, Charles E. and Commane, Roisin and Chang, Rachel Y-W and Dinardo, Steven J. and Henderson, John M. and Karion, Anna and Lindaas, Jakob and Melton, Joe R. and Miller, John B. and Sweeney, Colm and Wofsy, Steven C. and Michalak, Anna M.}, title = {A multiyear estimate of methane fluxes in Alaska from CARVE atmospheric observations}, journal = {GLOBAL BIOGEOCHEMICAL CYCLES}, year = {2016}, volume = {30}, number = {10}, pages = {1441-1453}, doi = {https://doi.org/10.1002/2016GB005419} }
Saunois, M., Bousquet, P., Poulter, B., Peregon, A., Ciais, P., Canadell, J.G., Dlugokencky, E.J., Etiope, G., Bastviken, D., Houweling, S., Janssens-Maenhout, G., Tubiello, F.N., Castaldi, S., Jackson, R.B., Alexe, M., Arora, V.K., Beerling, D.J., Bergamaschi, P., Blake, D.R., Brailsford, G., Brovkin, V., Bruhwiler, L., Crevoisier, C., Crill, P., Covey, K., Curry, C., Frankenberg, C., Gedney, N., Hoeglund-Isaksson, L., Ishizawa, M., Ito, A., Joos, F., Kim, H.-S., Kleinen, T., Krummel, P., Lamarque, J.-F., Langenfelds, R., Locatelli, R., Machida, T., Maksyutov, S., McDonald, K.C., Marshall, J., Melton, J.R., Morino, I., Naik, V., O'Doherty, S., Parmentier, F.-J.W., Patra, P.K., Peng, C., Peng, S., Peters, G.P., Pison, I., Prigent, C., Prinn, R., Ramonet, M., Riley, W.J., Saito, M., Santini, M., Schroeder, R., Simpson, I.J., Spahni, R., Steele, P., Takizawa, A., Thornton, B.F., Tian, H., Tohjima, Y., Viovy, N., Voulgarakis, A., van Weele, M., van der Werf, G.R., Weiss, R., Wiedinmyer, C., Wilton, D.J., Wiltshire, A., Worthy, D., Wunch, D., Xu, X., Yoshida, Y., Zhang, B., Zhang, Z. and Zhu, Q.	The global methane budget 2000-2012 [Abstract] [BibTeX]	2016	EARTH SYSTEM SCIENCE DATA Vol. 8(2), pp. 697-751	article	DOI
Abstract: The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase, making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (similar to biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). For the 2003-2012 decade, global methane emissions are estimated by top-down inversions at 558 TgCH(4) yr(-1), range 540-568. About 60% of global emissions are anthropogenic (range 50-65 %). Since 2010, the bottom-up global emission inventories have been closer to methane emissions in the most carbon-intensive Representative Concentrations Pathway (RCP8.5) and higher than all other RCP scenarios. Bottom-up approaches suggest larger global emissions (736 TgCH(4) yr(-1), range 596-884) mostly because of larger natural emissions from individual sources such as inland waters, natural wetlands and geological sources. Considering the atmospheric constraints on the top-down budget, it is likely that some of the individual emissions reported by the bottom-up approaches are overestimated, leading to too large global emissions. Latitudinal data from top-down emissions indicate a predominance of tropical emissions (similar to 64% of the global budget, <30 degrees N) as compared to mid (similar to 32 %, 30-60 degrees N) and high northern latitudes (similar to 4 %, 60-90 degrees N). Top-down inversions consistently infer lower emissions in China (similar to 58 TgCH(4) yr(-1), range 51-72, -14 %) and higher emissions in Africa (86 TgCH(4) yr(-1), range 73-108, + 19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models. The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30-40% on the estimated range for wetland emissions. Other priorities for improving the methane budget include the following: (i) the development of process-based models for inland-water emissions, (ii) the intensification of methane observations at local scale (flux measurements) to constrain bottom-up land surface models, and at regional scale (surface networks and satellites) to constrain top-down inversions, (iii) improvements in the estimation of atmospheric loss by OH, and (iv) improvements of the transport models integrated in top-down inversions. The data presented here can be downloaded from the Carbon Dioxide Information Analysis Center (http://doi.org/10.3334/CDIAC/GLOBAL_METHANE_BUDGET_2016_V1.1) and the Global Carbon Project.
BibTeX: @article{WOS:000390145300001, author = {Saunois, Marielle and Bousquet, Philippe and Poulter, Ben and Peregon, Anna and Ciais, Philippe and Canadell, Josep G. and Dlugokencky, Edward J. and Etiope, Giuseppe and Bastviken, David and Houweling, Sander and Janssens-Maenhout, Greet and Tubiello, Francesco N. and Castaldi, Simona and Jackson, Robert B. and Alexe, Mihai and Arora, Vivek K. and Beerling, David J. and Bergamaschi, Peter and Blake, Donald R. and Brailsford, Gordon and Brovkin, Victor and Bruhwiler, Lori and Crevoisier, Cyril and Crill, Patrick and Covey, Kristofer and Curry, Charles and Frankenberg, Christian and Gedney, Nicola and Hoeglund-Isaksson, Lena and Ishizawa, Misa and Ito, Akihiko and Joos, Fortunat and Kim, Heon-Sook and Kleinen, Thomas and Krummel, Paul and Lamarque, Jean-Francois and Langenfelds, Ray and Locatelli, Robin and Machida, Toshinobu and Maksyutov, Shamil and McDonald, Kyle C. and Marshall, Julia and Melton, Joe R. and Morino, Isamu and Naik, Vaishali and O'Doherty, Simon and Parmentier, Frans-Jan W. and Patra, Prabir K. and Peng, Changhui and Peng, Shushi and Peters, Glen P. and Pison, Isabelle and Prigent, Catherine and Prinn, Ronald and Ramonet, Michel and Riley, William J. and Saito, Makoto and Santini, Monia and Schroeder, Ronny and Simpson, Isobel J. and Spahni, Renato and Steele, Paul and Takizawa, Atsushi and Thornton, Brett F. and Tian, Hanqin and Tohjima, Yasunori and Viovy, Nicolas and Voulgarakis, Apostolos and van Weele, Michiel and van der Werf, Guido R. and Weiss, Ray and Wiedinmyer, Christine and Wilton, David J. and Wiltshire, Andy and Worthy, Doug and Wunch, Debra and Xu, Xiyan and Yoshida, Yukio and Zhang, Bowen and Zhang, Zhen and Zhu, Qiuan}, title = {The global methane budget 2000-2012}, journal = {EARTH SYSTEM SCIENCE DATA}, year = {2016}, volume = {8}, number = {2}, pages = {697-751}, doi = {https://doi.org/10.5194/essd-8-697-2016} }
Houweling, S., Bergamaschi, P., Chevallier, F., Heimann, M., Kaminski, T., Krol, M., Michalak, A.M. and Patra, P.	Global inverse modeling of CH4 sources and sinks: an overview of methods [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(1), pp. 235-256	article	DOI
Abstract: The aim of this paper is to present an overview of inverse modeling methods that have been developed over the years for estimating the global sources and sinks of CH4. It provides insight into how techniques and estimates have evolved over time and what the remaining shortcomings are. As such, it serves a didactical purpose of introducing apprentices to the field, but it also takes stock of developments so far and reflects on promising new directions. The main focus is on methodological aspects that are particularly relevant for CH4, such as its atmospheric oxidation, the use of methane isotopologues, and specific challenges in atmospheric transport modeling of CH4. The use of satellite retrievals receives special attention as it is an active field of methodological development, with special requirements on the sampling of the model and the treatment of data uncertainty. Regional scale flux estimation and attribution is still a grand challenge, which calls for new methods capable of combining information from multiple data streams of different measured parameters. A process model representation of sources and sinks in atmospheric transport inversion schemes allows the integrated use of such data. These new developments are needed not only to improve our understanding of the main processes driving the observed global trend but also to support international efforts to reduce greenhouse gas emissions.
BibTeX: @article{WOS:000392124200001, author = {Houweling, Sander and Bergamaschi, Peter and Chevallier, Frederic and Heimann, Martin and Kaminski, Thomas and Krol, Maarten and Michalak, Anna M. and Patra, Prabir}, title = {Global inverse modeling of CH4 sources and sinks: an overview of methods}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {1}, pages = {235-256}, doi = {https://doi.org/10.5194/acp-17-235-2017} }
Thornton, B.F., Wik, M. and Crill, P.M.	Double-counting challenges the accuracy of high-latitude methane inventories [Abstract] [BibTeX]	2016	GEOPHYSICAL RESEARCH LETTERS Vol. 43(24), pp. 12569-12577	article	DOI
Abstract: Quantification of the present and future contribution to atmospheric methane (CH4) from lakes, wetlands, fluvial systems, and, potentially, coastal waters remains an important unfinished task for balancing the global CH4 budget. Discriminating between these sources is crucial, especially across climate-sensitive Arctic and subarctic landscapes and waters. Yet basic underlying uncertainties remain, in such areas as total wetland area and definitions of wetlands, which can lead to conflation of wetlands and small ponds in regional studies. We discuss how in situ sampling choices, remote sensing limitations, and isotopic signature overlaps can lead to unintentional double-counting of CH4 emissions and propose that this double-counting can explain a pan-Arctic bottom-up estimate from published sources, 59.7 Tg yr(-1) (range 36.9-89.4 Tg yr(-1)) greatly exceeding the most recent top-down inverse modeled estimate of the pan-Arctic CH4 budget (23 +/- 5 Tg yr(-1)).
BibTeX: @article{WOS:000392741900032, author = {Thornton, Brett F. and Wik, Martin and Crill, Patrick M.}, title = {Double-counting challenges the accuracy of high-latitude methane inventories}, journal = {GEOPHYSICAL RESEARCH LETTERS}, year = {2016}, volume = {43}, number = {24}, pages = {12569-12577}, doi = {https://doi.org/10.1002/2016GL071772} }
France, J.L., Cain, M., Fisher, R.E., Lowry, D., Allen, G., O'Shea, S.J., Illingworth, S., Pyle, J., Warwick, N., Jones, B.T., Gallagher, M.W., Bower, K., Le Breton, M., Percival, C., Muller, J., Welpott, A., Bauguitte, S., George, C., Hayman, G.D., Manning, A.J., Myhre, C.L., Lanoiselle, M. and Nisbet, E.G.	Measurements of delta C-13 in CH4 and using particle dispersion modeling to characterize sources of Arctic methane within an air mass [Abstract] [BibTeX]	2016	JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 121(23), pp. 14257-14270	article	DOI
Abstract: A stratified air mass enriched in methane (CH4) was sampled at similar to 600m to similar to 2000m altitude, between the north coast of Norway and Svalbard as part of the Methane in the Arctic: Measurements and Modelling campaign on board the UK' s BAe-146-301 Atmospheric Research Aircraft. The approach used here, which combines interpretation of multiple tracers with transport modeling, enables better understanding of the emission sources that contribute to the background mixing ratios of CH4 in the Arctic. Importantly, it allows constraints to be placed on the location and isotopic bulk signature of the emission source(s). Measurements of delta C-13 in CH4 in whole air samples taken while traversing the air mass identified that the source(s) had a strongly depleted bulk delta C-13 CH4 isotopic signature of -70 (+/- 2.1)parts per thousand. Combined Numerical Atmospheric-dispersion Modeling Environment and inventory analysis indicates that the air mass was recently in the planetary boundary layer over northwest Russia and the Barents Sea, with the likely dominant source of methane being from wetlands in that region.
BibTeX: @article{WOS:000394520300028, author = {France, J. L. and Cain, M. and Fisher, R. E. and Lowry, D. and Allen, G. and O'Shea, S. J. and Illingworth, S. and Pyle, J. and Warwick, N. and Jones, B. T. and Gallagher, M. W. and Bower, K. and Le Breton, M. and Percival, C. and Muller, J. and Welpott, A. and Bauguitte, S. and George, C. and Hayman, G. D. and Manning, A. J. and Myhre, C. Lund and Lanoiselle, M. and Nisbet, E. G.}, title = {Measurements of delta C-13 in CH4 and using particle dispersion modeling to characterize sources of Arctic methane within an air mass}, journal = {JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, year = {2016}, volume = {121}, number = {23}, pages = {14257-14270}, doi = {https://doi.org/10.1002/2016JD026006} }
Bader, W., Bovy, B., Conway, S., Strong, K., Smale, D., Turner, A.J., Blumenstock, T., Boone, C., Coen, M.C., Coulon, A., Garcia, O., Griffith, D.T., Hase, F., Hausmann, P., Jones, N., Krummel, P., Murata, I., Morino, I., Nakajima, H., O'Doherty, S., Paton-Walsh, C., Robinson, J., Sandrin, R., Schneider, M., Servais, C., Sussmann, R. and Mahieu, E.	The recent increase of atmospheric methane from 10 years of ground-based NDACC FTIR observations since 2005 [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(3), pp. 2255-2277	article	DOI
Abstract: Changes of atmospheric methane total columns (CH4) since 2005 have been evaluated using Fourier transform infrared (FTIR) solar observations carried out at 10 ground-based sites, affiliated to the Network for Detection of Atmospheric Composition Change (NDACC). From this, we find an increase of atmospheric methane total columns of 0.31 +/- 0.03% year(-1) (2 sigma level of uncertainty) for the 2005-2014 period. Comparisons with in situ methane measurements at both local and global scales show good agreement. We used the GEOS-Chem chemical transport model tagged simulation, which accounts for the contribution of each emission source and one sink in the total methane, simulated over 2005-2012. After regridding according to NDACC vertical layering using a conservative regridding scheme and smoothing by convolving with respective FTIR seasonal averaging kernels, the GEOS-Chem simulation shows an increase of atmospheric methane total columns of 0.35 +/- 0.03% year(-1) between 2005 and 2012, which is in agreement with NDACC measurements over the same time period (0.30 +/- 0.04% year(-1), averaged over 10 stations). Analysis of the GEOS-Chem-tagged simulation allows us to quantify the contribution of each tracer to the global methane change since 2005. We find that natural sources such as wetlands and biomass burning contribute to the interannual variability of methane. However, anthropogenic emissions, such as coal mining, and gas and oil transport and exploration, which are mainly emitted in the Northern Hemisphere and act as secondary contributors to the global budget of methane, have played a major role in the increase of atmospheric methane observed since 2005. Based on the GEOS-Chem-tagged simulation, we discuss possible cause(s) for the increase of methane since 2005, which is still unexplained.
BibTeX: @article{WOS:000395118000003, author = {Bader, Whitney and Bovy, Benoit and Conway, Stephanie and Strong, Kimberly and Smale, Dan and Turner, Alexander J. and Blumenstock, Thomas and Boone, Chris and Coen, Martine Collaud and Coulon, Ancelin and Garcia, Omaira and Griffith, DavidW. T. and Hase, Frank and Hausmann, Petra and Jones, Nicholas and Krummel, Paul and Murata, Isao and Morino, Isamu and Nakajima, Hideaki and O'Doherty, Simon and Paton-Walsh, Clare and Robinson, John and Sandrin, Rodrigue and Schneider, Matthias and Servais, Christian and Sussmann, Ralf and Mahieu, Emmanuel}, title = {The recent increase of atmospheric methane from 10 years of ground-based NDACC FTIR observations since 2005}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {3}, pages = {2255-2277}, doi = {https://doi.org/10.5194/acp-17-2255-2017} }
Wei, D. and Wang, X.	Uncertainty and dynamics of natural wetland CH4 release in China: Research status and priorities [Abstract] [BibTeX]	2017	ATMOSPHERIC ENVIRONMENT Vol. 154, pp. 95-105	article	DOI
Abstract: Natural wetlands represent the largest single source of methane (CH4), a potent greenhouse gas. China is home to the world's fourth largest wetland area, and it is facing intense climate- and human-related impacts. The scientific community in China has invested considerable effort into investigating wetland CH4 release and its dynamics. Static chamber and eddy covariance observations have verified the temperature, water regime and air pressure as factors that regulate the diurnal and seasonal variation of CH4 release. Non-growing seasons, especially freezing thawing cycles, play a role in CH4 release. However, a knowledge gap still exists with respect to the inter-annual variability of CH4 release. Observations also suggest that water and temperature regimes control the micro- and macro-scale spatial pattern of CH4 release, respectively. Recent bookkeeping surveys, biogeochemical model simulations, and chemical transport model inversions, have narrowed the uncertainty range of national CH4 release to 2.46-3.20, 2.77-4.95 and 238-4.91 Tg CH4 yr(-1), respectively. Wetland loss (especially cropland conversion in Northeast China), despite climate changes, decreased CH4 release by 45.2%-52.2% from the 1950s-2000s, and by 13.2%-15.4% from the 1980s-2000s. However, future warmer temperatures and rising CO2 are predicted to strengthen national CH4 release by 32% (RCP2.6), 55% (RCP4.5) and 91% (RCP8.5) by the 2080s, albeit without the variation in wetland extent having been considered. Furthermore, future research should emphasize the mechanisms involved in CH4 release during freezing thawing cycles and interannual variability. Model data fusion of eddy covariance and manipulative experiments, especially warming and CO2 enrichment, would benefit estimations and projections of CH4 release. (C) 2017 Elsevier Ltd. All rights reserved.
BibTeX: @article{WOS:000397551800009, author = {Wei, Da and Wang, Xiaodan}, title = {Uncertainty and dynamics of natural wetland CH4 release in China: Research status and priorities}, journal = {ATMOSPHERIC ENVIRONMENT}, year = {2017}, volume = {154}, pages = {95-105}, doi = {https://doi.org/10.1016/j.atmosenv.2017.01.038} }
Thompson, R.L., Sasakawa, M., Machida, T., Aalto, T., Worthy, D., Lavric, J.V., Myhre, C.L. and Stohl, A.	Methane fluxes in the high northern latitudes for 2005-2013 estimated using a Bayesian atmospheric inversion [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(5), pp. 3553-3572	article	DOI
Abstract: We present methane (CH4) flux estimates for 2005 to 2013 from a Bayesian inversion focusing on the high northern latitudes (north of 50 degrees N). Our inversion is based on atmospheric transport modelled by the Lagrangian particle dispersion model FLEXPART and CH4 observations from 17 in situ and five discrete flask-sampling sites distributed over northern North America and Eurasia. CH4 fluxes are determined at monthly temporal resolution and on a variable grid with maximum resolution of 1 degrees x 1 degrees. Our inversion finds a CH4 source from the high northern latitudes of 82 to 84 Tg yr(-1), constituting similar to 15% of the global total, compared to 64 to 68 Tg yr(-1) (similar to 12 %) in the prior estimates. For northern North America, we estimate a mean source of 16.6 to 17.9 Tg yr(-1), which is dominated by fluxes in the Hudson Bay Lowlands (HBL) and western Canada, specifically the province of Alberta. Our estimate for the HBL, of 2.7 to 3.4 Tg yr(-1), is close to the prior estimate (which includes wetland fluxes from the land surface model, LPX-Bern) and to other independent inversion estimates. However, our estimate for Alberta, of 5.0 to 5.8 Tg yr(-1), is significantly higher than the prior (which also includes anthropogenic sources from the EDGAR-4.2FT2010 inventory). Since the fluxes from this region persist throughout the winter, this may signify that the anthropogenic emissions are underestimated. For northern Eurasia, we find a mean source of 52.2 to 55.5 Tg yr(-1), with a strong contribution from fluxes in the Western Siberian Lowlands (WSL) for which we estimate a source of 19.3 to 19.9 Tg yr(-1). Over the 9-year inversion period, we find significant year-to-year variations in the fluxes, which in North America, and specifically in the HBL, appear to be driven at least in part by soil temperature, while in the WSL, the variability is more dependent on soil moisture. Moreover, we find significant positive trends in the CH4 fluxes in North America of 0.38 to 0.57 Tg yr(-2), and northern Eurasia of 0.76 to 1.09 Tg yr(-2). In North America, this could be due to an increase in soil temperature, while in North Eurasia, specifically Russia, the trend is likely due, at least in part, to an increase in anthropogenic sources.
BibTeX: @article{WOS:000397827900004, author = {Thompson, Rona L. and Sasakawa, Motoki and Machida, Toshinobu and Aalto, Tuula and Worthy, Doug and Lavric, Jost V. and Myhre, Cathrine Lund and Stohl, Andreas}, title = {Methane fluxes in the high northern latitudes for 2005-2013 estimated using a Bayesian atmospheric inversion}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {5}, pages = {3553-3572}, doi = {https://doi.org/10.5194/acp-17-3553-2017} }
Tsuruta, A., Aalto, T., Backman, L., Hakkarainen, J., van der Laan-Luijkx, I.T., Krol, M.C., Spahni, R., Houweling, S., Laine, M., Dlugokencky, E., Gomez-Pelaez, A.J., van der Schoot, M., Langenfelds, R., Ellul, R., Arduini, J., Apadula, F., Gerbig, C., Feist, D.G., Kivi, R., Yoshida, Y. and Peters, W.	Global methane emission estimates for 2000-2012 from CarbonTracker Europe-CH4 v1.0 [Abstract] [BibTeX]	2017	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 10(3)	article	DOI
Abstract: We present a global distribution of surface methane (CH4) emission estimates for 2000-2012 derived using the CarbonTracker Europe-CH4 (CTE-CH4) data assimilation system. In CTE-CH4, anthropogenic and biospheric CH4 emissions are simultaneously estimated based on constraints of global atmospheric in situ CH4 observations. The system was configured to either estimate only anthropogenic or biospheric sources per region, or to estimate both categories simultaneously. The latter increased the number of optimizable parameters from 62 to 78. In addition, the differences between two numerical schemes available to perform turbulent vertical mixing in the atmospheric transport model TM5 were examined. Together, the system configurations encompass important axes of uncertainty in inversions and allow us to examine the robustness of the flux estimates. The posterior emission estimates are further evaluated by comparing simulated atmospheric CH4 to surface in situ observations, vertical profiles of CH4 made by aircraft, remotely sensed dry-air total column-averaged mole fraction (XCH4) from the Total Carbon Column Observing Network (TCCON), and XCH4 from the Greenhouse gases Observing Satellite (GOSAT). The evaluation with non-assimilated observations shows that posterior XCH4 is better matched with the retrievals when the vertical mixing scheme with faster interhemispheric exchange is used. Estimated posterior mean total global emissions during 2000-2012 are 516 +/- 51 Tg CH4 yr(-1), with an increase of 18 Tg CH4 yr(-1) from 2000-2006 to 2007-2012. The increase is mainly driven by an increase in emissions from South American temperate, Asian temperate and Asian tropical TransCom regions. In addition, the increase is hardly sensitive to different model configurations (< 2 Tg CH4 yr(-1) difference), and much smaller than suggested by EDGAR v4.2 FT2010 inventory (33 Tg CH4 yr(-1)), which was used for prior anthropogenic emission estimates. The result is in good agreement with other published estimates from inverse modelling studies (16-20 Tg CH4 yr(-1)). However, this study could not conclusively separate a small trend in biospheric emissions (-5 to +6.9 Tg CH4 yr(-1)) from the much larger trend in anthropogenic emissions (15-27 Tg CH4 yr(-1)). Finally, we find that the global and North American CH4 balance could be closed over this time period without the previously suggested need to strongly increase anthropogenic CH4 emissions in the United States. With further developments, especially on the treatment of the atmospheric CH4 sink, we expect the data assimilation system presented here will be able to contribute to the ongoing interpretation of changes in this important greenhouse gas budget.
BibTeX: @article{WOS:000398898800001, author = {Tsuruta, Aki and Aalto, Tuula and Backman, Leif and Hakkarainen, Janne and van der Laan-Luijkx, Ingrid T. and Krol, Maarten C. and Spahni, Renato and Houweling, Sander and Laine, Marko and Dlugokencky, Ed and Gomez-Pelaez, Angel J. and van der Schoot, Marcel and Langenfelds, Ray and Ellul, Raymond and Arduini, Jgor and Apadula, Francesco and Gerbig, Christoph and Feist, Dietrich G. and Kivi, Rigel and Yoshida, Yukio and Peters, Wouter}, title = {Global methane emission estimates for 2000-2012 from CarbonTracker Europe-CH4 v1.0}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2017}, volume = {10}, number = {3}, doi = {https://doi.org/10.5194/gmd-10-1261-2017} }
Jiang, Z., Worden, J.R., Worden, H., Deeter, M., Jones, D.B.A., Arellano, A.F. and Henze, D.K.	A 15-year record of CO emissions constrained by MOPITT CO observations [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(7), pp. 4565-4583	article	DOI
Abstract: Long-term measurements from satellites and surface stations have demonstrated a decreasing trend of tropospheric carbon monoxide (CO) in the Northern Hemisphere over the past decade. Likely explanations for this decrease include changes in anthropogenic, fires, and/or biogenic emissions or changes in the primary chemical sink hydroxyl radical (OH). Using remotely sensed CO measurements from the Measurement of Pollution in the Troposphere (MOPITT) satellite instrument, in situ methyl chloroform (MCF) measurements from the World Data Centre for Greenhouse Gases (WDCGG) and the adjoint of the GEOS-Chem model, we estimate the change in global CO emissions from 2001 to 2015. We show that the loss rate of MCF varied by 0.2% in the past 15 years, indicating that changes in global OH distributions do not explain the recent decrease in CO. Our two-step inversion approach for estimating CO emissions is intended to mitigate the effect of bias errors in the MOPITT data as well as model errors in transport and chemistry, which are the primary factors contributing to the uncertainties when quantifying CO emissions using these remotely sensed data. Our results confirm that the decreasing trend of tropospheric CO in the Northern Hemisphere is due to decreasing CO emissions from anthropogenic and biomass burning sources. In particular, we find decreasing CO emissions from the United States and China in the past 15 years, and unchanged anthropogenic CO emissions from Europe since 2008. We find decreasing trends of biomass burning CO emissions from boreal North America, boreal Asia and South America, but little change over Africa. In contrast to prior results, we find that a positive trend in CO emissions is likely for India and southeast Asia.
BibTeX: @article{WOS:000399401900001, author = {Jiang, Zhe and Worden, John R. and Worden, Helen and Deeter, Merritt and Jones, Dylan B. A. and Arellano, Avelino F. and Henze, Daven K.}, title = {A 15-year record of CO emissions constrained by MOPITT CO observations}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {7}, pages = {4565-4583}, doi = {https://doi.org/10.5194/acp-17-4565-2017} }
Bruhwiler, L.M., Basu, S., Bergamaschi, P., Bousquet, P., Dlugokencky, E., Houweling, S., Ishizawa, M., Kim, H.S., Locatelli, R., Maksyutov, S., Montzka, S., Pandey, S., Patra, P.K., Petron, G., Saunois, M., Sweeney, C., Schwietzke, S., Tans, P. and Weatherhead, E.C.	US CH4 emissions from oil and gas production: Have recent large increases been detected? [Abstract] [BibTeX]	2017	JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 122(7), pp. 4070-4083	article	DOI
Abstract: Recent studies have proposed significant increases in CH4 emissions possibly from oil and gas (O&G) production, especially for the U.S. where O&G production has reached historically high levels over the past decade. In this study, we show that an ensemble of time-dependent atmospheric inversions constrained by calibrated atmospheric observations of surface CH4 mole fraction, with some including space-based retrievals of column average CH4 mole fractions, suggests that North American CH4 emissions have been flat over years spanning 2000 through 2012. Estimates of emission trends using zonal gradients of column average CH4 calculated relative to an upstream background are not easy to make due to atmospheric variability, relative insensitivity of column average CH4 to surface emissions at regional scales, and fast zonal synoptic transport. In addition, any trends in continental enhancements of column average CH4 are sensitive to how the upstream background is chosen, and model simulations imply that short-term (4years or less) trends in column average CH4 horizontal gradients of up to 1.5ppb/yr can occur just from interannual transport variability acting on a strong latitudinal CH4 gradient. Finally, trends in spatial gradients calculated from space-based column average CH4 can be significantly biased (>2-3ppb/yr) due to the nonuniform and seasonally varying temporal coverage of satellite retrievals. Plain Language Summary In this paper we address recent claims of significant increases in methane emissions from U.S. oil and gas production. We find that such claims are inconsistent with observations by examining atmospheric inversions and observations from the NOAA aircraft monitoring program. Furthermore, we show how atmospheric variability, sampling biases, and choice of upwind background can lead to spurious trends in atmospheric column average methane when using both in situ and space-based retrievals.
BibTeX: @article{WOS:000400172000023, author = {Bruhwiler, L. M. and Basu, S. and Bergamaschi, P. and Bousquet, P. and Dlugokencky, E. and Houweling, S. and Ishizawa, M. and Kim, H. -S. and Locatelli, R. and Maksyutov, S. and Montzka, S. and Pandey, S. and Patra, P. K. and Petron, G. and Saunois, M. and Sweeney, C. and Schwietzke, S. and Tans, P. and Weatherhead, E. C.}, title = {US CH4 emissions from oil and gas production: Have recent large increases been detected?}, journal = {JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, year = {2017}, volume = {122}, number = {7}, pages = {4070-4083}, doi = {https://doi.org/10.1002/2016JD026157} }
Fisher, R.E., France, J.L., Lowry, D., Lanoiselle, M., Brownlow, R., Pyle, J.A., Cain, M., Warwick, N., Skiba, U.M., Drewer, J., Dinsmore, K.J., Leeson, S.R., Bauguitte, S.J.B., Wellpott, A., O'Shea, S.J., Allen, G., Gallagher, M.W., Pitt, J., Percival, C.J., Bower, K., George, C., Hayman, G.D., Aalto, T., Lohila, A., Aurela, M., Laurila, T., Crill, P.M., McCalley, C.K. and Nisbet, E.G.	Measurement of the C-13 isotopic signature of methane emissions from northern European wetlands [Abstract] [BibTeX]	2017	GLOBAL BIOGEOCHEMICAL CYCLES Vol. 31(3), pp. 605-623	article	DOI
Abstract: Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. In this study, isotopic signatures of emissions in the Fennoscandian Arctic have been determined in chambers over wetland, in the air 0.3 to 3m above the wetland surface and by aircraft sampling from 100m above wetlands up to the stratosphere. Overall, the methane flux to atmosphere has a coherent delta C-13 isotopic signature of -71 +/- 1%, measured in situ on the ground in wetlands. This is in close agreement with delta C-13 isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast, results from wetlands in Canadian boreal forest farther south gave isotopic signatures of -67 +/- 1%. Wetland emissions dominate the local methane source measured over the European Arctic in summer. Chamber measurements demonstrate a highly variable methane flux and isotopic signature, but the results from air sampling within wetland areas show that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures. The study suggests that for boreal wetlands (>60 degrees N) global and regional modeling can use an isotopic signature of -71 parts per thousand to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.
BibTeX: @article{WOS:000400695400010, author = {Fisher, Rebecca E. and France, James L. and Lowry, David and Lanoiselle, Mathias and Brownlow, Rebecca and Pyle, John A. and Cain, Michelle and Warwick, Nicola and Skiba, Ute M. and Drewer, Julia and Dinsmore, Kerry J. and Leeson, Sarah R. and Bauguitte, Stephane J. -B. and Wellpott, Axel and O'Shea, Sebastian J. and Allen, Grant and Gallagher, Martin W. and Pitt, Joseph and Percival, Carl J. and Bower, Keith and George, Charles and Hayman, Garry D. and Aalto, Tuula and Lohila, Annalea and Aurela, Mika and Laurila, Tuomas and Crill, Patrick M. and McCalley, Carmody K. and Nisbet, Euan G.}, title = {Measurement of the C-13 isotopic signature of methane emissions from northern European wetlands}, journal = {GLOBAL BIOGEOCHEMICAL CYCLES}, year = {2017}, volume = {31}, number = {3}, pages = {605-623}, doi = {https://doi.org/10.1002/2016GB005504} }
Peters, C.N., Bennartz, R. and Hornberger, G.M.	Satellite-derived methane emissions from inundation in Bangladesh [Abstract] [BibTeX]	2017	JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Vol. 122(5), pp. 1137-1155	article	DOI
Abstract: The uncertainty in methane (CH4) source strength of rice fields and wetlands is particularly high in South Asia CH4 budgets. We used satellite observations of CH4 column mixing ratios from Atmospheric Infrared Sounder (AIRS), Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), and Greenhouse Gases Observing Satellite (GOSAT) to estimate the contribution of Bangladesh emissions to atmospheric CH4 concentrations. Using satellite-derived inundation area as a proxy for source area, we developed a simple inverse advection model that estimates average annual CH4 surface fluxes to be 4, 9, and 19mgCH(4)m(-2)h(-1) in AIRS, SCIAMACHY, and GOSAT, respectively. Despite this variability, our flux estimates varied over a significantly narrower range than reported values for CH4 surface fluxes from a survey of 32 studies reporting ground-based observations between 0 and 260mgCH(4)m(-2)h(-1). Upscaling our satellite-derived surface flux estimates, we estimated total annual CH4 emissions for Bangladesh to be 1.33.2, 1.82.0, 3.11.6Tgyr(-1), depending on the satellite. Our estimates of total emissions are in line with the median of total emission values for Bangladesh reported in earlier studies. Plain Language Summary The extent of methane emissions from flooded areas, such as wetlands and rice paddies, is not well understood, particularly in South Asia. This study uses satellite observations of atmospheric methane and flooding to explore seasonal fluctuation in methane emissions from Bangladesh. Our findings suggest methane emissions similar to previously thought.
BibTeX: @article{WOS:000403487600010, author = {Peters, C. N. and Bennartz, R. and Hornberger, G. M.}, title = {Satellite-derived methane emissions from inundation in Bangladesh}, journal = {JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES}, year = {2017}, volume = {122}, number = {5}, pages = {1137-1155}, doi = {https://doi.org/10.1002/2016JG003740} }
Schwietzke, S., Petron, G., Conley, S., Pickering, C., Mielke-Maday, I., Dlugokencky, E.J., Tans, P.P., Vaughn, T., Bell, C., Zimmerle, D., Wolter, S., King, C.W., White, A.B., Coleman, T., Bianco, L. and Schnell, R.C.	Improved Mechanistic Understanding of Natural Gas Methane Emissions from Spatially Resolved Aircraft Measurements [Abstract] [BibTeX]	2017	ENVIRONMENTAL SCIENCE & TECHNOLOGY Vol. 51(12), pp. 7286-7294	article	DOI
Abstract: Divergence in recent oil and gas related methane emission estimates between aircraft studies (basin total for a midday window) and emissions inventories (annualized regional and national statistics) indicate the need for better understanding the experimental design, including temporal and spatial alignment and interpretation of results. Our aircraft-based methane emission estimates in a major U.S. shale gas basin resolved from west to east show (i) similar spatial distributions for 2 days, (ii) strong spatial correlations with reported NG production (R-2 = 0.75) and active gas well pad count (R-2 = 0.81), and (iii) 2x higher emissions in the western half (normalized by gas production) despite relatively homogeneous dry gas and well characteristics. Operator reported hourly activity data show that midday episodic emissions from manual liquid unloadings (a routine operation in this basin and elsewhere) could explain similar to 1/3 of the total emissions detected midday by the aircraft and similar to 2/3 of the west east difference in emissions. The 22% emission difference between both days further emphasizes that episodic sources can substantially impact midday methane emissions and that aircraft may detect daily peak emissions rather than daily averages that are generally employed in emissions inventories. While the aircraft approach is valid, quantitative, and independent, our study sheds new light on the interpretation of previous basin scale aircraft studies, and provides an improved mechanistic understanding of oil and gas related methane emissions.
BibTeX: @article{WOS:000404087400072, author = {Schwietzke, Stefan and Petron, Gabrielle and Conley, Stephen and Pickering, Cody and Mielke-Maday, Ingrid and Dlugokencky, Edward J. and Tans, Pieter P. and Vaughn, Tim and Bell, Clay and Zimmerle, Daniel and Wolter, Sonja and King, Clark W. and White, Allen B. and Coleman, Timothy and Bianco, Laura and Schnell, Russell C.}, title = {Improved Mechanistic Understanding of Natural Gas Methane Emissions from Spatially Resolved Aircraft Measurements}, journal = {ENVIRONMENTAL SCIENCE & TECHNOLOGY}, year = {2017}, volume = {51}, number = {12}, pages = {7286-7294}, doi = {https://doi.org/10.1021/acs.est.7b01810} }
Thonat, T., Saunois, M., Bousquet, P., Pison, I., Tan, Z., Zhuang, Q., Crill, P.M., Thornton, B.F., Bastviken, D., Dlugokencky, E.J., Zimov, N., Laurila, T., Hatakka, J., Hermansen, O. and Worthy, D.E.J.	Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(13), pp. 8371-8394	article	DOI
Abstract: Understanding the recent evolution of methane emissions in the Arctic is necessary to interpret the global methane cycle. Emissions are affected by significant uncertainties and are sensitive to climate change, leading to potential feedbacks. A polar version of the CHIMERE chemistry-transport model is used to simulate the evolution of tropospheric methane in the Arctic during 2012, including all known regional anthropogenic and natural sources, in particular freshwater emissions which are often overlooked in methane modelling. CHIMERE simulations are compared to atmospheric continuous observations at six measurement sites in the Arctic region. In winter, the Arctic is dominated by anthropogenic emissions; emissions from continental seepages and oceans, including from the East Siberian Arctic Shelf, can contribute significantly in more limited areas. In summer, emissions from wetland and freshwater sources dominate across the whole region. The model is able to reproduce the seasonality and synoptic variations of methane measured at the different sites. We find that all methane sources significantly affect the measurements at all stations at least at the synoptic scale, except for biomass burning. In particular, freshwater systems play a decisive part in summer, representing on average between 11 and 26% of the simulated Arctic methane signal at the sites. This indicates the relevance of continuous observations to gain a mechanistic understanding of Arctic methane sources. Sensitivity tests reveal that the choice of the land-surface model used to prescribe wetland emissions can be critical in correctly representing methane mixing ratios. The closest agreement with the observations is reached when using the two wetland models which have emissions peaking in August-September, while all others reach their maximum in JuneJuly. Such phasing provides an interesting constraint on wetland models which still have large uncertainties at present. Also testing different freshwater emission inventories leads to large differences in modelled methane. Attempts to include methane sinks (OH oxidation and soil uptake) reduced the model bias relative to observed atmospheric methane. The study illustrates how multiple sources, having different spatiotemporal dynamics and magnitudes, jointly influence the overall Arctic methane budget, and highlights ways towards further improved assessments.
BibTeX: @article{WOS:000405372800001, author = {Thonat, Thibaud and Saunois, Marielle and Bousquet, Philippe and Pison, Isabelle and Tan, Zeli and Zhuang, Qianlai and Crill, Patrick M. and Thornton, Brett F. and Bastviken, David and Dlugokencky, Ed J. and Zimov, Nikita and Laurila, Tuomas and Hatakka, Juha and Hermansen, Ove and Worthy, Doug E. J.}, title = {Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {13}, pages = {8371-8394}, doi = {https://doi.org/10.5194/acp-17-8371-2017} }
Poulter, B., Bousquet, P., Canadell, J.G., Ciais, P., Peregon, A., Saunois, M., Arora, V.K., Beerling, D.J., Brovkin, V., Jones, C.D., Joos, F., Gedney, N., Ito, A., Kleinen, T., Koven, C.D., McDonald, K., Melton, J.R., Peng, C., Peng, S., Prigent, C., Schroeder, R., Riley, W.J., Saito, M., Spahni, R., Tian, H., Taylor, L., Viovy, N., Wilton, D., Wiltshire, A., Xu, X., Zhang, B., Zhang, Z. and Zhu, Q.	Global wetland contribution to 2000-2012 atmospheric methane growth rate dynamics [Abstract] [BibTeX]	2017	ENVIRONMENTAL RESEARCH LETTERS Vol. 12(9)	article	DOI
Abstract: Increasing atmospheric methane (CH4) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH4 as a greenhouse gas, its atmospheric growth rate and dynamics over the past two decades, which include a stabilization period (1999-2006), followed by renewed growth starting in 2007, remain poorly understood. We provide an updated estimate of CH4 emissions from wetlands, the largest natural global CH4 source, for 2000-2012 using an ensemble of biogeochemical models constrained with remote sensing surface inundation and inventory-based wetland area data. Between 2000-2012, boreal wetland CH4 emissions increased by 1.2 Tg yr(-1) (-0.2-3.5 Tg yr(-1)), tropical emissions decreased by 0.9 Tg yr(-1) (-3.2-1.1 Tg yr(-1)), yet globally, emissions remained unchanged at 184 +/- 22 Tg yr(-1). Changing air temperature was responsible for increasing high-latitude emissions whereas declines in low-latitude wetland area decreased tropical emissions; both dynamics are consistent with features of predicted centennial-scale climate change impacts on wetland CH4 emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH4 emissions have not contributed significantly to the period of renewed atmospheric CH4 growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH4 emissions, and a decrease in the atmospheric oxidative sink.
BibTeX: @article{WOS:000410925500001, author = {Poulter, Benjamin and Bousquet, Philippe and Canadell, Josep G. and Ciais, Philippe and Peregon, Anna and Saunois, Marielle and Arora, Vivek K. and Beerling, David J. and Brovkin, Victor and Jones, Chris D. and Joos, Fortunat and Gedney, Nicola and Ito, Akihito and Kleinen, Thomas and Koven, Charles D. and McDonald, Kyle and Melton, Joe R. and Peng, Changhui and Peng, Shushi and Prigent, Catherine and Schroeder, Ronny and Riley, William J. and Saito, Makoto and Spahni, Renato and Tian, Hanqin and Taylor, Lyla and Viovy, Nicolas and Wilton, David and Wiltshire, Andy and Xu, Xiyan and Zhang, Bowen and Zhang, Zhen and Zhu, Qiuan}, title = {Global wetland contribution to 2000-2012 atmospheric methane growth rate dynamics}, journal = {ENVIRONMENTAL RESEARCH LETTERS}, year = {2017}, volume = {12}, number = {9}, doi = {https://doi.org/10.1088/1748-9326/aa8391} }
Saunois, M., Bousquet, P., Poulter, B., Peregon, A., Ciais, P., Canadell, J.G., Dlugokencky, E.J., Etiope, G., Bastviken, D., Houweling, S., Janssens-Maenhout, G., Tubiello, F.N., Castaldi, S., Jackson, R.B., Alexe, M., Arora, V.K., Beerling, D.J., Bergamaschi, P., Blake, D.R., Brailsford, G., Bruhwiler, L., Crevoisier, C., Crill, P., Covey, K., Frankenberg, C., Gedney, N., Hoeglund-Isaksson, L., Ishizawa, M., Ito, A., Joos, F., Kim, H.-S., Kleinen, T., Krummel, P., Lamarque, J.-F., Langenfelds, R., Locatelli, R., Machida, T., Maksyutov, S., Melton, J.R., Morino, I., Naik, V., O'Doherty, S., Parmentier, F.-J., Patra, P.K., Peng, C., Peng, S., Peters, G.P., Pison, I., Prinn, R., Ramonet, M., Riley, W.J., Saito, M., Santini, M., Schroeder, R., Simpson, I.J., Spahni, R., Takizawa, A., Thornton, B.F., Tian, H., Tohjima, Y., Viovy, N., Voulgarakis, A., Weiss, R., Wilton, D.J., Wiltshire, A., Worthy, D., Wunch, D., Xu, X., Yoshida, Y., Zhang, B., Zhang, Z. and Zhu, Q.	Variability and quasi-decadal changes in the methane budget over the period 2000-2012 [Abstract] [BibTeX]	2017	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 17(18), pp. 11135-11161	article	DOI
Abstract: Following the recent Global Carbon Project (GCP) synthesis of the decadal methane (CH4) budget over 2000-2012 (Saunois et al., 2016), we analyse here the same dataset with a focus on quasi-decadal and inter-annual variability in CH4 emissions. The GCP dataset integrates results from top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models (including process-based models for estimating land surface emissions and atmospheric chemistry), inventories of anthropogenic emissions, and data-driven approaches. The annual global methane emissions from top-down studies, which by construction match the observed methane growth rate within their uncertainties, all show an increase in total methane emissions over the period 2000-2012, but this increase is not linear over the 13 years. Despite differences between individual studies, the mean emission anomaly of the top-down ensemble shows no significant trend in total methane emissions over the period 2000-2006, during the plateau of atmospheric methane mole fractions, and also over the period 2008-2012, during the renewed atmospheric methane increase. However, the top-down ensemble mean produces an emission shift between 2006 and 2008, leading to 22 [16-32] Tg CH4 yr(-1) higher methane emissions over the period 2008-2012 compared to 2002-2006. This emission increase mostly originated from the tropics, with a smaller contribution from mid-latitudes and no significant change from boreal regions. The regional contributions remain uncertain in top-down studies. Tropical South America and South and East Asia seem to contribute the most to the emission increase in the tropics. However, these two regions have only limited atmospheric measurements and remain therefore poorly constrained. The sectorial partitioning of this emission increase between the periods 2002-2006 and 2008-2012 differs from one atmospheric inversion study to another. However, all top-down studies suggest smaller changes in fossil fuel emissions (from oil, gas, and coal industries) compared to the mean of the bottom-up inventories included in this study. This difference is partly driven by a smaller emission change in China from the top-down studies compared to the estimate in the Emission Database for Global Atmospheric Research (EDGARv4.2) inventory, which should be revised to smaller values in a near future. We apply isotopic signatures to the emission changes estimated for individual studies based on five emission sectors and find that for six individual top-down studies (out of eight) the average isotopic signature of the emission changes is not consistent with the observed change in atmospheric (CH4)-C-13. However, the partitioning in emission change derived from the ensemble mean is consistent with this isotopic constraint. At the global scale, the top-down ensemble mean suggests that the dominant contribution to the resumed atmospheric CH4 growth after 2006 comes from microbial sources (more from agriculture and waste sectors than from natural wetlands), with an uncertain but smaller contribution from fossil CH4 emissions. In addition, a decrease in biomass burning emissions (in agreement with the biomass burning emission databases) makes the balance of sources consistent with atmospheric (CH4)-C-13 observations. In most of the top-down studies included here, OH concentrations are considered constant over the years (seasonal variations but without any inter-annual variability). As a result, the methane loss (in particular through OH oxidation) varies mainly through the change in methane concentrations and not its oxidants. For these reasons, changes in the methane loss could not be properly investigated in this study, although it may play a significant role in the recent atmospheric methane changes as briefly discussed at the end of the paper.
BibTeX: @article{WOS:000411253700003, author = {Saunois, Marielle and Bousquet, Philippe and Poulter, Ben and Peregon, Anna and Ciais, Philippe and Canadell, Josep G. and Dlugokencky, Edward J. and Etiope, Giuseppe and Bastviken, David and Houweling, Sander and Janssens-Maenhout, Greet and Tubiello, Francesco N. and Castaldi, Simona and Jackson, Robert B. and Alexe, Mihai and Arora, Vivek K. and Beerling, David J. and Bergamaschi, Peter and Blake, Donald R. and Brailsford, Gordon and Bruhwiler, Lori and Crevoisier, Cyril and Crill, Patrick and Covey, Kristofer and Frankenberg, Christian and Gedney, Nicola and Hoeglund-Isaksson, Lena and Ishizawa, Misa and Ito, Akihiko and Joos, Fortunat and Kim, Heon-Sook and Kleinen, Thomas and Krummel, Paul and Lamarque, Jean-Francois and Langenfelds, Ray and Locatelli, Robin and Machida, Toshinobu and Maksyutov, Shamil and Melton, Joe R. and Morino, Isamu and Naik, Vaishali and O'Doherty, Simon and Parmentier, Frans-JanW. and Patra, Prabir K. and Peng, Changhui and Peng, Shushi and Peters, Glen P. and Pison, Isabelle and Prinn, Ronald and Ramonet, Michel and Riley, William J. and Saito, Makoto and Santini, Monia and Schroeder, Ronny and Simpson, Isobel J. and Spahni, Renato and Takizawa, Atsushi and Thornton, Brett F. and Tian, Hanqin and Tohjima, Yasunori and Viovy, Nicolas and Voulgarakis, Apostolos and Weiss, Ray and Wilton, David J. and Wiltshire, Andy and Worthy, Doug and Wunch, Debra and Xu, Xiyan and Yoshida, Yukio and Zhang, Bowen and Zhang, Zhen and Zhu, Qiuan}, title = {Variability and quasi-decadal changes in the methane budget over the period 2000-2012}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2017}, volume = {17}, number = {18}, pages = {11135-11161}, doi = {https://doi.org/10.5194/acp-17-11135-2017} }
Hartery, S., Commane, R., Lindaas, J., Sweeney, C., Henderson, J., Mountain, M., Steiner, N., McDonald, K., Dinardo, S.J., Miller, C.E., Wofsy, S.C. and Chang, R.Y.W.	Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska [Abstract] [BibTeX]	2018	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 18(1), pp. 185-202	article	DOI
Abstract: Methane (CH4) is the second most important greenhouse gas but its emissions from northern regions are still poorly constrained. In this study, we analyze a subset of in situ CH4 aircraft observations made over Alaska during the growing seasons of 2012-2014 as part of the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE). Net surface CH4 fluxes are estimated using a Lagrangian particle dispersion model which quantitatively links surface emissions from Alaska and the western Yukon with observations of enhanced CH4 in the mixed layer. We estimate that between May and September, net CH4 emissions from the region of interest were 2.2 +/- 0.5 Tg, 1.9 +/- 0.4 Tg, and 2.3 +/- 0.6 Tg of CH4 for 2012, 2013, and 2014, respectively. If emissions are only attributed to two biogenic eco-regions within our domain, then tundra regions were the predominant source, accounting for over half of the overall budget despite only representing 18% of the total surface area. Bo-real regions, which cover a large part of the study region, accounted for the remainder of the emissions. Simple multiple linear regression analysis revealed that, overall, CH4 fluxes were largely driven by soil temperature and elevation. In regions specifically dominated by wetlands, soil temperature and moisture at 10 cm depth were important explanatory variables while in regions that were not wetlands, soil temperature and moisture at 40 cm depth were more important, suggesting deeper methanogenesis in drier soils. Although similar environmental drivers have been found in the past to control CH4 emissions at local scales, this study shows that they can be used to generate a statistical model to estimate the regional-scale net CH4 budget.
BibTeX: @article{WOS:000419530300002, author = {Hartery, Sean and Commane, Roisin and Lindaas, Jakob and Sweeney, Colm and Henderson, John and Mountain, Marikate and Steiner, Nicholas and McDonald, Kyle and Dinardo, Steven J. and Miller, Charles E. and Wofsy, Steven C. and Chang, Rachel Y. -W.}, title = {Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2018}, volume = {18}, number = {1}, pages = {185-202}, doi = {https://doi.org/10.5194/acp-18-185-2018} }
van der Velde, I.R., Miller, J.B., van der Molen, M.K., Tans, P.P., Vaughn, B.H., White, J.W.C., Schaefer, K. and Peters, W.	The CarbonTracker Data Assimilation System for CO2 and delta C-13 (CTDAS-C13 v1.0): retrieving information on land-atmosphere exchange processes [Abstract] [BibTeX]	2018	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 11(1), pp. 283-304	article	DOI
Abstract: To improve our understanding of the global carbon balance and its representation in terrestrial biosphere models, we present here a first dual-species application of the CarbonTracker Data Assimilation System (CTDAS). The system's modular design allows for assimilating multiple atmospheric trace gases simultaneously to infer exchange fluxes at the Earth surface. In the prototype discussed here, we interpret signals recorded in observed carbon dioxide (CO2) along with observed ratios of its stable isotopologues (CO2)-C-13/(CO2)-C-12 (delta C-13). The latter is in particular a valuable tracer to untangle CO2 exchange from land and oceans. Potentially, it can also be used as a proxy for continent-wide drought stress in plants, largely because the ratio of (CO2)-C-13 and (CO2)-C-12 molecules removed from the atmosphere by plants is dependent on moisture conditions. The dual-species CTDAS system varies the net exchange fluxes of both (CO2)-C-13 and CO2 in ocean and terrestrial biosphere models to create an ensemble of (CO2)-C-13 and CO2 fluxes that propagates through an atmospheric transport model. Based on differences between observed and simulated (CO2)-C-13 and CO2 mole fractions (and thus delta C-13) our Bayesian minimization approach solves for weekly adjustments to both net fluxes and isotopic terrestrial discrimination that minimizes the difference between observed and estimated mole fractions. With this system, we are able to estimate changes in terrestrial delta C-13 exchange on seasonal and continental scales in the Northern Hemisphere where the observational network is most dense. Our results indicate a decrease in stomatal conductance on a continent-wide scale during a severe drought. These changes could only be detected after applying combined atmospheric CO2 and delta C-13 constraints as done in this work. The additional constraints on surface CO2 exchange from delta C-13 observations neither affected the estimated carbon fluxes nor compromised our ability to match observed CO2 variations. The prototype presented here can be of great benefit not only to study the global carbon balance but also to potentially function as a data-driven diagnostic to assess multiple leaf-level exchange parameterizations in carbon-climate models that influence the CO2, water, isotope, and energy balance.
BibTeX: @article{WOS:000423149900001, author = {van der Velde, Ivar R. and Miller, John B. and van der Molen, Michiel K. and Tans, Pieter P. and Vaughn, Bruce H. and White, James W. C. and Schaefer, Kevin and Peters, Wouter}, title = {The CarbonTracker Data Assimilation System for CO2 and delta C-13 (CTDAS-C13 v1.0): retrieving information on land-atmosphere exchange processes}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2018}, volume = {11}, number = {1}, pages = {283-304}, doi = {https://doi.org/10.5194/gmd-11-283-2018} }
Hoesly, R.M., Smith, S.J., Feng, L., Klimont, Z., Janssens-Maenhout, G., Pitkanen, T., Seibert, J.J., Vu, L., Andres, R.J., Bolt, R.M., Bond, T.C., Dawidowski, L., Kholod, N., Kurokawa, J.-i., Li, M., Liu, L., Lu, Z., Moura, M.C.P., O'Rourke, P.R. and Zhang, Q.	Historical (1750-2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS) [Abstract] [BibTeX]	2018	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 11(1), pp. 369-408	article	DOI
Abstract: We present a new data set of annual historical (1750-2014) anthropogenic chemically reactive gases (CO, CH4, NH3, NOx, SO2, NMVOCs), carbonaceous aerosols (black carbon - BC, and organic carbon - OC), and CO2 developed with the Community Emissions Data System (CEDS). We improve upon existing inventories with a more consistent and reproducible methodology applied to all emission species, updated emission factors, and recent estimates through 2014. The data system relies on existing energy consumption data sets and regional and country-specific inventories to produce trends over recent decades. All emission species are consistently estimated using the same activity data over all time periods. Emissions are provided on an annual basis at the level of country and sector and gridded with monthly seasonality. These estimates are comparable to, but generally slightly higher than, existing global inventories. Emissions over the most recent years are more uncertain, particularly in low-and middle-income regions where country-specific emission inventories are less available. Future work will involve refining and updating these emission estimates, estimating emissions' uncertainty, and publication of the system as open-source software.
BibTeX: @article{WOS:000423507000001, author = {Hoesly, Rachel M. and Smith, Steven J. and Feng, Leyang and Klimont, Zbigniew and Janssens-Maenhout, Greet and Pitkanen, Tyler and Seibert, Jonathan J. and Linh Vu and Andres, Robert J. and Bolt, Ryan M. and Bond, Tami C. and Dawidowski, Laura and Kholod, Nazar and Kurokawa, June-ichi and Li, Meng and Liu, Liang and Lu, Zifeng and Moura, Maria Cecilia P. and O'Rourke, Patrick R. and Zhang, Qiang}, title = {Historical (1750-2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS)}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2018}, volume = {11}, number = {1}, pages = {369-408}, doi = {https://doi.org/10.5194/gmd-11-369-2018} }
Feinberg, A.I., Coulon, A., Stenke, A., Schwietzke, S. and Peter, T.	Isotopic source signatures: Impact of regional variability on the delta(CH4)-C-13 trend and spatial distribution [Abstract] [BibTeX]	2018	ATMOSPHERIC ENVIRONMENT Vol. 174, pp. 99-111	article	DOI
Abstract: The atmospheric methane growth rate has fluctuated over the past three decades, signifying variations in methane sources and sinks. Methane isotopic ratios (delta(CH4)-C-13) differ between emission categories, and can therefore be used to distinguish which methane sources have changed. However, isotopic modelling studies have mainly focused on uncertainties in methane emissions rather than uncertainties in isotopic source signatures. We simulated atmospheric delta(CH4)-C-13 for the period 1990-2010 using the global chemistry-climate model SOCOL. Empirically-derived regional variability in the isotopic signatures was introduced in a suite of sensitivity simulations. These simulations were compared to a baseline simulation with commonly used global mean isotopic signatures. We investigated coal, natural gas/oil, wetland, livestock, and biomass burning source signatures to determine whether regional variations impact the observed isotopic trend and spatial distribution. Based on recently published source signature datasets, our calculated global mean isotopic signatures are in general lighter than the commonly used values. Trends in several isotopic signatures were also apparent during the period 1990-2010. Tropical livestock emissions grew during the 2000s, introducing isotopically heavier livestock emissions since tropical livestock consume more C-4 vegetation than midlatitude livestock. Chinese coal emissions, which are isotopically heavy compared to other coals, increase during the 2000s leading to higher global values of delta(CH4)-C-13 for coal emissions. EDGAR v4.2 emissions disagree with the observed atmospheric isotopic trend for almost all simulations, confirming past doubts about this emissions inventory. The agreement between the modelled and observed delta(CH4)-C-13 interhemispheric differences improves when regional source signatures are used. Even though the simulated results are highly dependent on the choice of methane emission inventories, they emphasize that the commonly used global mean signatures are inadequate. Regional isotopic signatures should be employed in modelling studies that try to constrain methane emission inventories.
BibTeX: @article{WOS:000423888400010, author = {Feinberg, Aryeh I. and Coulon, Ancelin and Stenke, Andrea and Schwietzke, Stefan and Peter, Thomas}, title = {Isotopic source signatures: Impact of regional variability on the delta(CH4)-C-13 trend and spatial distribution}, journal = {ATMOSPHERIC ENVIRONMENT}, year = {2018}, volume = {174}, pages = {99-111}, doi = {https://doi.org/10.1016/j.atmosenv.2017.11.037} }
Feldman, D.R., Collins, W.D., Biraud, S.C., Risser, M.D., Turner, D.D., Gero, P.J., Tadic, J., Helmig, D., Xie, S., Mlawer, E.J., Shippert, T.R. and Torn, M.S.	Observationally derived rise in methane surface forcing mediated by water vapour trends [Abstract] [BibTeX]	2018	NATURE GEOSCIENCE Vol. 11(4), pp. 238+	article	DOI
Abstract: Atmospheric methane (CH4) mixing ratios exhibited a plateau between 1995 and 2006 and have subsequently been increasing. While there are a number of competing explanations for the temporal evolution of this greenhouse gas, these prominent features in the temporal trajectory of atmospheric CH4 are expected to perturb the surface energy balance through radiative forcing, largely due to the infrared radiative absorption features of CH4. However, to date this has been determined strictly through radiative transfer calculations. Here, we present a quantified observation of the time series of clear-sky radiative forcing by CH4 at the surface from 2002 to 2012 at a single site derived from spectroscopic measurements along with line-by-line calculations using ancillary data. There was no significant trend in CH4 forcing between 2002 and 2006, but since then, the trend in forcing was 0.026 +/- 0.006 (99.7% CI) W m(2) yr(-1). The seasonal-cycle amplitude and secular trends in observed forcing are influenced by a corresponding seasonal cycle and trend in atmospheric CH4. However, we find that we must account for the overlapping absorption effects of atmospheric water vapour (H2O) and CH4 to explain the observations fully. Thus, the determination of CH4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH4 and the vertically resolved trends in H2O.
BibTeX: @article{WOS:000429131600014, author = {Feldman, D. R. and Collins, W. D. and Biraud, S. C. and Risser, M. D. and Turner, D. D. and Gero, P. J. and Tadic, J. and Helmig, D. and Xie, S. and Mlawer, E. J. and Shippert, T. R. and Torn, M. S.}, title = {Observationally derived rise in methane surface forcing mediated by water vapour trends}, journal = {NATURE GEOSCIENCE}, year = {2018}, volume = {11}, number = {4}, pages = {238+}, doi = {https://doi.org/10.1038/s41561-018-0085-9} }
Dean, J.F., Middelburg, J.J., Rockmann, T., Aerts, R., Blauw, L.G., Egger, M., Jetten, M.S.M., de Jong, A.E.E., Meisel, O.H., Rasigraf, O., Slomp, C.P., in't Zandt, M.H. and Dolman, A.J.	Methane Feedbacks to the Global Climate System in a Warmer World [Abstract] [BibTeX]	2018	REVIEWS OF GEOPHYSICS Vol. 56(1), pp. 207-250	article	DOI
Abstract: Methane (CH4) is produced in many natural systems that are vulnerable to change under a warming climate, yet current CH4 budgets, as well as future shifts in CH4 emissions, have high uncertainties. Climate change has the potential to increase CH4 emissions from critical systems such as wetlands, marine and freshwater systems, permafrost, and methane hydrates, through shifts in temperature, hydrology, vegetation, landscape disturbance, and sea level rise. Increased CH4 emissions from these systems would in turn induce further climate change, resulting in a positive climate feedback. Here we synthesize biological, geochemical, and physically focused CH4 climate feedback literature, bringing together the key findings of these disciplines. We discuss environment-specific feedback processes, including the microbial, physical, and geochemical interlinkages and the timescales on which they operate, and present the current state of knowledge of CH4 climate feedbacks in the immediate and distant future. The important linkages between microbial activity and climate warming are discussed with the aim to better constrain the sensitivity of the CH4 cycle to future climate predictions. We determine that wetlands will form the majority of the CH4 climate feedback up to 2100. Beyond this timescale, CH4 emissions from marine and freshwater systems and permafrost environments could become more important. Significant CH4 emissions to the atmosphere from the dissociation of methane hydrates are not expected in the near future. Our key findings highlight the importance of quantifying whether CH4 consumption can counterbalance CH4 production under future climate scenarios. Plain Language Summary Methane is a powerful greenhouse gas, second only to carbon dioxide in its importance to climate change. Methane production in natural environments is controlled by factors that are themselves influenced by climate. Increased methane production can warm the Earth, which can in turn cause methane to be produced at a faster rate - this is called a positive climate feedback. Here we describe the most important natural environments for methane production that have the potential to produce a positive climate feedback. We discuss how these feedbacks may develop in the coming centuries under predicted climate warming using a cross-disciplinary approach. We emphasize the importance of considering methane dynamics at all scales, especially its production and consumption and the role microorganisms play in both these processes, to our understanding of current and future global methane emissions. Marrying large-scale geophysical studies with site-scale biogeochemical and microbial studies will be key to this.
BibTeX: @article{WOS:000430130800007, author = {Dean, Joshua F. and Middelburg, Jack J. and Rockmann, Thomas and Aerts, Rien and Blauw, Luke G. and Egger, Matthias and Jetten, Mike S. M. and de Jong, Anniek E. E. and Meisel, Ove H. and Rasigraf, Olivia and Slomp, Caroline P. and in't Zandt, Michiel H. and Dolman, A. J.}, title = {Methane Feedbacks to the Global Climate System in a Warmer World}, journal = {REVIEWS OF GEOPHYSICS}, year = {2018}, volume = {56}, number = {1}, pages = {207-250}, doi = {https://doi.org/10.1002/2017RG000559} }
Lin, X., Ciais, P., Bousquet, P., Ramonet, M., Yin, Y., Balkanski, Y., Cozic, A., Delmotte, M., Evangeliou, N., Indira, N.K., Locatelli, R., Peng, S., Piao, S., Saunois, M., Swathi, P.S., Wang, R., Yver-Kwok, C., Tiwari, Y.K. and Zhou, L.	Simulating CH4 and CO2 over South and East Asia using the zoomed chemistry transport model LMDz-INCA [Abstract] [BibTeX]	2018	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 18(13), pp. 9475-9497	article	DOI
Abstract: The increasing availability of atmospheric measurements of greenhouse gases (GHGs) from surface stations can improve the retrieval of their fluxes at higher spatial and temporal resolutions by inversions, provided that transport models are able to properly represent the variability of concentrations observed at different stations. South and East Asia (SEA; the study area in this paper including the regions of South Asia and East Asia) is a region with large and very uncertain emissions of carbon dioxide (CO2) and methane (CH4), the most potent anthropogenic GHGs. Monitoring networks have expanded greatly during the past decade in this region, which should contribute to reducing uncertainties in estimates of regional GHG budgets. In this study, we simulate concentrations of CH4 and CO2 using zoomed versions (abbreviated as ``ZAs'') of the global chemistry transport model LMDz-INCA, which have fine horizontal resolutions of similar to 0.66 degrees in longitude and similar to 0.51 degrees in latitude over SEA and coarser resolutions elsewhere. The concentrations of CH4 and CO2 simulated from ZAs are compared to those from the same model but with standard model grids of 2.50 degrees in longitude and 1.27 degrees in latitude (abbreviated as ``STs''), both prescribed with the same natural and anthropogenic fluxes. Model performance is evaluated for each model version at multi-annual, seasonal, synoptic and diurnal scales, against a unique observation dataset including 39 global and regional stations over SEA and around the world. Results show that ZAs improve the overall representation of CH4 annual gradients between stations in SEA, with reduction of RMSE by 16-20% compared to STs. The model improvement mainly results from reduction in representation error at finer horizontal resolutions and thus better characterization of the CH4 concentration gradients related to scattered distributed emission sources. However, the performance of ZAs at a specific station as compared to STs is more sensitive to errors in meteorological forcings and surface fluxes, especially when short-term variabilities or stations close to source regions are examined. This highlights the importance of accurate a priori CH4 surface fluxes in high-resolution transport modeling and inverse studies, particularly regarding locations and magnitudes of emission hotspots. Model performance for CO2 suggests that the CO2 surface fluxes have not been prescribed with sufficient accuracy and resolution, especially the spatiotemporally varying carbon exchange between land surface and atmosphere. In addition, the representation of the CH4 and CO2 short-term variabilities is also limited by model's ability to simulate boundary layer mixing and mesoscale transport in complex terrains, emphasizing the need to improve sub-grid physical parameterizations in addition to refinement of model resolutions.
BibTeX: @article{WOS:000437733900003, author = {Lin, Xin and Ciais, Philippe and Bousquet, Philippe and Ramonet, Michel and Yin, Yi and Balkanski, Yves and Cozic, Anne and Delmotte, Marc and Evangeliou, Nikolaos and Indira, Nuggehalli K. and Locatelli, Robin and Peng, Shushi and Piao, Shilong and Saunois, Marielle and Swathi, Panangady S. and Wang, Rong and Yver-Kwok, Camille and Tiwari, Yogesh K. and Zhou, Lingxi}, title = {Simulating CH4 and CO2 over South and East Asia using the zoomed chemistry transport model LMDz-INCA}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2018}, volume = {18}, number = {13}, pages = {9475-9497}, doi = {https://doi.org/10.5194/acp-18-9475-2018} }
Tadic, J.M. and Biraud, S.C.	An Approach to Estimate Atmospheric Greenhouse Gas Total Columns Mole Fraction from Partial Column Sampling [Abstract] [BibTeX]	2018	ATMOSPHERE Vol. 9(7)	article	DOI
Abstract: This study presents a new conceptual approach to estimate total column mole fractions of CO2 and CH4 using partial column data. It provides a link between airborne in situ and remote sensing observations of greenhouse gases. The method relies on in situ observations, external ancillary sources of information (e.g., atmospheric transport models), and a regression kriging framework. We evaluate our new approach using National Oceanic and Atmospheric Administration's (NOAA's) AirCore program-in situ vertical profiles of CO2 and CH4 collected from weather balloons. Our paper shows that under the specific conditions of this study and assumption of unbiasedness, airborne observations up to 6500-9500 m altitude are required to achieve comparable total column CO2 mole fraction uncertainty as the Total Carbon Column Observing Network (TCCON) network provides, given as a precision of the ratio between observed and true total column-integrated mole fraction, assuming 400 ppm XCO2 (2 sigma, e.g., 0.8 ppm). If properly calibrated, our approach could be applied to vertical profiles of CO2 collected from aircraft using a few flask samples, while retaining similar uncertainty level. Our total column CH4 estimates, by contrast, are less accurate than TCCON's. Aircrafts are not as spatially constrained as TCCON ground stations, so our approach adds value to aircraft-based vertical profiles for evaluating remote sensing platforms.
BibTeX: @article{WOS:000445141400011, author = {Tadic, Jovan M. and Biraud, Sebastien C.}, title = {An Approach to Estimate Atmospheric Greenhouse Gas Total Columns Mole Fraction from Partial Column Sampling}, journal = {ATMOSPHERE}, year = {2018}, volume = {9}, number = {7}, doi = {https://doi.org/10.3390/atmos9070247} }
Treat, C.C., Marushchak, M.E., Voigt, C., Zhang, Y., Tan, Z., Zhuang, Q., Virtanen, T.A., Rasanen, A., Biasi, C., Hugelius, G., Kaverin, D., Miller, P.A., Stendel, M., Romanovsky, V., Rivkin, F., Martikainen, P.J. and Shurpali, N.J.	Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic [Abstract] [BibTeX]	2018	GLOBAL CHANGE BIOLOGY Vol. 24(11), pp. 5188-5204	article	DOI
Abstract: Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a similar to 100-km(2) sub-Arctic tundra region in northeast European Russia for the period of 2006-2015 using process-based biogeochemical models. Modeled net annual CO2 fluxes ranged from --300 g C m(-2) year(-1) [net uptake] in a willow fen to 3 g Cm-2 year(-1) [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from -0.2 to 22.3 g Cm-2 year(-1) at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%-25%) in comparison with variability among the land cover types (150%). Using high-resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost-free fens. Using a lower resolution for land cover classification resulted in a 20%-65% underestimation of regional CH4 flux relative to high-resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.
BibTeX: @article{WOS:000447760300016, author = {Treat, Claire C. and Marushchak, Maija E. and Voigt, Carolina and Zhang, Yu and Tan, Zeli and Zhuang, Qianlai and Virtanen, Tarmo A. and Rasanen, Aleksi and Biasi, Christina and Hugelius, Gustaf and Kaverin, Dmitry and Miller, Paul A. and Stendel, Martin and Romanovsky, Vladimir and Rivkin, Felix and Martikainen, Pertti J. and Shurpali, Narasinha J.}, title = {Tundra landscape heterogeneity, not interannual variability, controls the decadal regional carbon balance in the Western Russian Arctic}, journal = {GLOBAL CHANGE BIOLOGY}, year = {2018}, volume = {24}, number = {11}, pages = {5188-5204}, doi = {https://doi.org/10.1111/gcb.14421} }
Dimdore-Miles, O.B., Palmer, P.I. and Bruhwiler, L.P.	Detecting changes in Arctic methane emissions: limitations of the inter-polar difference of atmospheric mole fractions [Abstract] [BibTeX]	2018	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 18(24), pp. 17895-17907	article	DOI
Abstract: We consider the utility of the annual inter-polar difference (IPD) as a metric for changes in Arctic emissions of methane (CH4). The IPD has been previously defined as the difference between weighted annual means of CH4 mole fraction data collected at stations from the two polar regions (defined as latitudes poleward of 53 degrees N and 53 degrees S, respectively). This subtraction approach (IPD) implicitly assumes that extra-polar CH4 emissions arrive within the same calendar year at both poles. We show using a continuous version of the IPD that the metric includes not only changes in Arctic emissions but also terms that represent atmospheric transport of air masses from lower latitudes to the polar regions. We show the importance of these atmospheric transport terms in understanding the IPD using idealized numerical experiments with the TM5 global 3-D atmospheric chemistry transport model that is run from 1980 to 2010. A northern mid-latitude pulse in January 1990, which increases prior emission distributions, arrives at the Arctic with a higher mole fraction and similar or equal to 12 months earlier than at the Antarctic. The perturbation at the poles subsequently decays with an e-folding lifetime of similar or equal to 4 years. A similarly timed pulse emitted from the tropics arrives with a higher value at the Antarctic similar or equal to 11 months earlier than at the Arctic. This perturbation decays with an e-folding lifetime of similar or equal to 7 years. These simulations demonstrate that the assumption of symmetric transport of extra-polar emissions to the poles is not realistic, resulting in considerable IPD variations due to variations in emissions and atmospheric transport. We assess how well the annual IPD can detect a constant annual growth rate of Arctic emissions for three scenarios, 0.5 %, 1 %, and 2 %, superimposed on signals from lower latitudes, including random noise. We find that it can take up to 16 years to detect the smallest prescribed trend in Arctic emissions at the 95% confidence level. Scenarios with higher, but likely unrealistic, growth in Arctic emissions are detected in less than a decade. We argue that a more reliable measurement-driven approach would require data collected from all latitudes, emphasizing the importance of maintaining a global monitoring network to observe decadal changes in atmospheric greenhouse gases.
BibTeX: @article{WOS:000453427000003, author = {Dimdore-Miles, Oscar B. and Palmer, Paul I. and Bruhwiler, Lori P.}, title = {Detecting changes in Arctic methane emissions: limitations of the inter-polar difference of atmospheric mole fractions}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2018}, volume = {18}, number = {24}, pages = {17895-17907}, doi = {https://doi.org/10.5194/acp-18-17895-2018} }
Miller, S.M., Michalak, A.M., Detmers, R.G., Hasekamp, O.P., Bruhwiler, L.M.P. and Schwietzke, S.	China's coal mine methane regulations have not curbed growing emissions [Abstract] [BibTeX]	2019	NATURE COMMUNICATIONS Vol. 10	article	DOI
Abstract: Anthropogenic methane emissions from China are likely greater than in any other country in the world. The largest fraction of China's anthropogenic emissions is attributable to coal mining, but these emissions may be changing; China enacted a suite of regulations for coal mine methane (CMM) drainage and utilization that came into full effect in 2010. Here, we use methane observations from the GOSAT satellite to evaluate recent trends in total anthropogenic and natural emissions from Asia with a particular focus on China. We find that emissions from China rose by 1.1 +/- 0.4 Tg CH(4)yr(-1) from 2010 to 2015, culminating in total anthropogenic and natural emissions of 61.5 +/- 2.7 Tg CH4 in 2015. The observed trend is consistent with pre-2010 trends and is largely attributable to coal mining. These results indicate that China's CMM regulations have had no discernible impact on the continued increase in Chinese methane emissions.
BibTeX: @article{WOS:000456957900001, author = {Miller, Scot M. and Michalak, Anna M. and Detmers, Robert G. and Hasekamp, Otto P. and Bruhwiler, Lori M. P. and Schwietzke, Stefan}, title = {China's coal mine methane regulations have not curbed growing emissions}, journal = {NATURE COMMUNICATIONS}, year = {2019}, volume = {10}, doi = {https://doi.org/10.1038/s41467-018-07891-7} }
Ishizawa, M., Chan, D., Worthy, D., Chan, E., Vogel, F. and Maksyutov, S.	Analysis of atmospheric CH4 in Canadian Arctic and estimation of the regional CH4 fluxes [Abstract] [BibTeX]	2019	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 19(7), pp. 4637-4658	article	DOI
Abstract: The Canadian Arctic (> 60 degrees N, 60-141 degrees W) may undergo drastic changes if the Arctic warming trend continues. For methane (CH4), Arctic reservoirs are large and widespread, and the climate feedbacks from such changes may be potentially substantial. Current bottom-up and top-down estimates of the regional CH4 flux range widely. This study analyzes the recent observations of atmospheric CH4 from five arctic monitoring sites and presents estimates of the regional CH4 fluxes for 2012-2015. The observational data reveal sizeable synoptic summertime enhancements in the atmospheric CH4 that are distinguishable from background variations, which indicate strong regional fluxes (primarily wetland and biomass burning CH4 emissions) around Behchoko and Inuvik in the western Canadian Arctic. Three regional Bayesian inversion modelling systems with two Lagrangian particle dispersion models and three meteorological datasets are applied to estimate fluxes for the Canadian Arctic and show relatively robust results in amplitude and temporal variations across different transport models, prior fluxes, and subregion masking. The estimated mean total CH4 flux for the entire Canadian Arctic is 1.8 +/- 0.6 Tg CH4 yr(-1). The flux estimate is partitioned into biomass burning of 0.3 +/- 0.1 Tg CH4 yr(-1) and the remaining natural (wetland) flux of 1.5 +/- 0.5 Tg CH4 yr(-1). The summer natural CH4 flux estimates clearly show inter-annual variability that is positively correlated with surface temperature anomalies. The results indicate that years with warmer summer conditions result in more wetland CH4 emissions. More data and analysis are required to statistically characterize the dependence of regional CH4 fluxes on the climate in the Arctic. These Arctic measurement sites will aid in quantifying the inter-annual variations and long-term trends in CH4 emissions in the Canadian Arctic.
BibTeX: @article{WOS:000463861600004, author = {Ishizawa, Misa and Chan, Douglas and Worthy, Doug and Chan, Elton and Vogel, Felix and Maksyutov, Shamil}, title = {Analysis of atmospheric CH4 in Canadian Arctic and estimation of the regional CH4 fluxes}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2019}, volume = {19}, number = {7}, pages = {4637-4658}, doi = {https://doi.org/10.5194/acp-19-4637-2019} }
Peltola, O., Vesala, T., Gao, Y., Raty, O., Alekseychik, P., Aurela, M., Chojnicki, B., Desai, A.R., Dolman, A.J., Euskirchen, E.S., Friborg, T., Goeckede, M., Helbig, M., Humphreys, E., Jackson, R.B., Jocher, G., Joos, F., Klatt, J., Knox, S.H., Kowalska, N., Kutzbach, L., Lienert, S., Lohila, A., Mammarella, I., Nadeau, D.F., Nilsson, M.B., Oechel, W.C., Peichl, M., Pypker, T., Quinton, W., Rinne, J., Sachs, T., Samson, M., Schmid, H.P., Sonnentag, O., Wille, C., Zona, D. and Aalto, T.	Monthly gridded data product of northern wetland methane emissions based on upscaling eddy covariance observations [Abstract] [BibTeX]	2019	EARTH SYSTEM SCIENCE DATA Vol. 11(3), pp. 1263-1289	article	DOI
Abstract: Natural wetlands constitute the largest and most uncertain source of methane (CH4) to the atmosphere and a large fraction of them are found in the northern latitudes. These emissions are typically estimated using process (''bottom-up'') or inversion (''top-down'') models. However, estimates from these two types of models are not independent of each other since the top-down estimates usually rely on the a priori estimation of these emissions obtained with process models. Hence, independent spatially explicit validation data are needed. Here we utilize a random forest (RF) machine-learning technique to upscale CH4 eddy covariance flux measurements from 25 sites to estimate CH4 wetland emissions from the northern latitudes (north of 45 degrees N). Eddy covariance data from 2005 to 2016 are used for model development. The model is then used to predict emissions during 2013 and 2014. The predictive performance of the RF model is evaluated using a leave-one-site-out cross-validation scheme. The performance (Nash-Sutcliffe model efficiency = 0.47) is comparable to previous studies upscaling net ecosystem exchange of carbon dioxide and studies comparing process model output against site-level CH4 emission data. The global distribution of wetlands is one major source of uncertainty for upscaling CH4. Thus, three wetland distribution maps are utilized in the upscaling. Depending on the wetland distribution map, the annual emissions for the northern wetlands yield 32 (22.3-41.2, 95% confidence interval calculated from a RF model ensemble), 31 (21.4-39.9) or 38 (25.9-49.5) Tg(CH4) yr(-1). To further evaluate the uncertainties of the upscaled CH4 flux data products we also compared them against output from two process models (LPX-Bern and WetCHARTs), and methodological issues related to CH4 flux upscaling are discussed. The monthly upscaled CH4 flux data products are available at https://doi.org/10.5281/zenodo.2560163.
BibTeX: @article{WOS:000482519900001, author = {Peltola, Olli and Vesala, Timo and Gao, Yao and Raty, Olle and Alekseychik, Pavel and Aurela, Mika and Chojnicki, Bogdan and Desai, Ankur R. and Dolman, Albertus J. and Euskirchen, Eugenie S. and Friborg, Thomas and Goeckede, Mathias and Helbig, Manuel and Humphreys, Elyn and Jackson, Robert B. and Jocher, Georg and Joos, Fortunat and Klatt, Janina and Knox, Sara H. and Kowalska, Natalia and Kutzbach, Lars and Lienert, Sebastian and Lohila, Annalea and Mammarella, Ivan and Nadeau, Daniel F. and Nilsson, Mats B. and Oechel, Walter C. and Peichl, Matthias and Pypker, Thomas and Quinton, William and Rinne, Janne and Sachs, Torsten and Samson, Mateusz and Schmid, Hans Peter and Sonnentag, Oliver and Wille, Christian and Zona, Donatella and Aalto, Tuula}, title = {Monthly gridded data product of northern wetland methane emissions based on upscaling eddy covariance observations}, journal = {EARTH SYSTEM SCIENCE DATA}, year = {2019}, volume = {11}, number = {3}, pages = {1263-1289}, doi = {https://doi.org/10.5194/essd-11-1263-2019} }
Thornton, B.F., Geibel, M.C., Crill, P.M., Humborg, C. and Morth, C.-M.	Comment on ``Understanding the Permafrost-Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf'' [Abstract] [BibTeX]	2019	GEOSCIENCES Vol. 9(9)	article	DOI
Abstract: The recent paper in Geosciences, ``Understanding the Permafrost-Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf'' by Shakhova, Semiletov, and Chuvilin, (henceforth ``S2019''), contains a number of false statements about our 2016 paper, ``Methane fluxes from the sea to the atmosphere across the Siberian shelf seas'', (henceforth ``T2016''). S2019 use three paragraphs of section 5 of their paper to claim methodological errors and issues in T2016. Notably they claim that in T2016, we systematically removed data outliers including data with high methane concentrations; this claim is false. While we appreciate that flawed methodologies can be a problem in any area of science, in this case, the claims made in S2019 are simply false. In this comment, we detail the incorrect claims made in S2019 regarding T2016, and then discuss some additional problematic aspects of S2019.
BibTeX: @article{WOS:000487634500022, author = {Thornton, Brett F. and Geibel, Marc C. and Crill, Patrick M. and Humborg, Christoph and Morth, Carl-Magnus}, title = {Comment on ``Understanding the Permafrost-Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf''}, journal = {GEOSCIENCES}, year = {2019}, volume = {9}, number = {9}, doi = {https://doi.org/10.3390/geosciences9090384} }
Tsuruta, A., Aalto, T., Backman, L., Krol, M.C., Peters, W., Lienert, S., Joos, F., Miller, P.A., Zhang, W., Laurila, T., Hatakka, J., Leskinen, A., Lehtinen, K.E.J., Peltola, O., Vesala, T., Levula, J., Dlugokencky, E., Heimann, M., Kozlova, E., Aurela, M., Lohila, A., Kauhaniemi, M. and Gomez-Pelaez, A.J.	Methane budget estimates in Finland from the CarbonTracker Europe-CH4 data assimilation system [Abstract] [BibTeX]	2019	TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY Vol. 71	article	DOI
Abstract: We estimated the CH4 budget in Finland for 2004-2014 using the CTE-CH4 data assimilation system with an extended atmospheric CH4 observation network of seven sites from Finland to surrounding regions (Hyytiala, Kjolnes, Kumpula, Pallas, Puijo, Sodankyla, and Uto). The estimated average annual total emission for Finland is 0.6 +/- 0.5 Tg CH4 yr(-1). Sensitivity experiments show that the posterior biospheric emission estimates for Finland are between 0.3 and 0.9 Tg CH4 yr(-1), which lies between the LPX-Bern-DYPTOP (0.2 Tg CH4 yr(-1)) and LPJG-WHyMe (2.2 Tg CH4 yr(-1)) process-based model estimates. For anthropogenic emissions, we found that the EDGAR v4.2 FT2010 inventory (0.4 Tg CH4 yr(-1)) is likely to overestimate emissions in southernmost Finland, but the extent of overestimation and possible relocation of emissions are difficult to derive from the current observation network. The posterior emission estimates were especially reliant on prior information in central Finland. However, based on analysis of posterior atmospheric CH4, we found that the anthropogenic emission distribution based on a national inventory is more reliable than the one based on EDGAR v4.2 FT2010. The contribution of total emissions in Finland to global total emissions is only about 0.13%, and the derived total emissions in Finland showed no trend during 2004-2014. The model using optimized emissions was able to reproduce observed atmospheric CH4 at the sites in Finland and surrounding regions fairly well (correlation > 0.75, bias < +/- 7 ppb), supporting adequacy of the observations to be used in atmospheric inversion studies. In addition to global budget estimates, we found that CTE-CH4 is also applicable for regional budget estimates, where small scale (1 degrees x1 degrees in this case) optimization is possible with a dense observation network.
BibTeX: @article{WOS:000498977700001, author = {Tsuruta, Aki and Aalto, Tuula and Backman, Leif and Krol, Maarten C. and Peters, Wouter and Lienert, Sebastian and Joos, Fortunat and Miller, Paul A. and Zhang, Wenxin and Laurila, Tuomas and Hatakka, Juha and Leskinen, Ari and Lehtinen, Kari E. J. and Peltola, Olli and Vesala, Timo and Levula, Janne and Dlugokencky, Ed and Heimann, Martin and Kozlova, Elena and Aurela, Mika and Lohila, Annalea and Kauhaniemi, Mari and Gomez-Pelaez, Angel J.}, title = {Methane budget estimates in Finland from the CarbonTracker Europe-CH4 data assimilation system}, journal = {TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY}, year = {2019}, volume = {71}, doi = {https://doi.org/10.1080/16000889.2018.1565030} }
Ganesan, A.L., Schwietzke, S., Poulter, B., Arnold, T., Lan, X., Rigby, M., Vogel, F.R., van der Werf, G.R., Janssens-Maenhout, G., Boesch, H., Pandey, S., Manning, A.J., Jackson, R.B., Nisbet, E.G. and Manning, M.	Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement [Abstract] [BibTeX]	2019	GLOBAL BIOGEOCHEMICAL CYCLES Vol. 33(12), pp. 1475-1512	article	DOI
Abstract: The 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 degrees C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process-based models of the main sectors of CH4 emissions-proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country-specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations-developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of (CH4)-C-13, CH3D, (CH4)-C-14, and clumped isotopes, creating isotopic reference materials for international-scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements-advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector-level emissions, and in the development of time and space resolved national inventories. These and other recommendations are proposed for the major areas of CH4 science with the aim of improving capability in the coming decade to quantify atmospheric CH4 budgets on the scales necessary for the success of climate policies.
BibTeX: @article{WOS:000503923900001, author = {Ganesan, Anita L. and Schwietzke, Stefan and Poulter, Benjamin and Arnold, Tim and Lan, Xin and Rigby, Matt and Vogel, Felix R. and van der Werf, Guido R. and Janssens-Maenhout, Greet and Boesch, Hartmut and Pandey, Sudhanshu and Manning, Alistair J. and Jackson, Robert B. and Nisbet, Euan G. and Manning, Martin}, title = {Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement}, journal = {GLOBAL BIOGEOCHEMICAL CYCLES}, year = {2019}, volume = {33}, number = {12}, pages = {1475-1512}, doi = {https://doi.org/10.1029/2018GB006065} }
Schaefer, H.	On the Causes and Consequences of Recent Trends in Atmospheric Methane [Abstract] [BibTeX]	2019	CURRENT CLIMATE CHANGE REPORTS Vol. 5(4), pp. 259-274	article	DOI
Abstract: Purpose of Review To investigate which processes cause the current increase in atmospheric methane in the context of future interactions between climate change, the methane cycle and policy decisions. Recent Findings There is evidence for various contributors to emission increases or reduced removal of atmospheric methane. No single process can explain the methane rise and remain consistent with available data. Reconstructions of recent changes in the methane budget do not converge as to the dominant contributor to the rise. A plausible scenario includes increasing emissions from agriculture and fossil fuels while biomass burning is reduced, with possible contributions from wetlands and a weakened sink. Summary Further studies are needed to identify contributors to the methane rise for targeted emission reductions and adaptation to changes in natural methane sources and sinks. Mitigation plans must address the methane rise and possible consequences from a climate-methane feedback.
BibTeX: @article{WOS:000517127500001, author = {Schaefer, Hinrich}, title = {On the Causes and Consequences of Recent Trends in Atmospheric Methane}, journal = {CURRENT CLIMATE CHANGE REPORTS}, year = {2019}, volume = {5}, number = {4}, pages = {259-274}, doi = {https://doi.org/10.1007/s40641-019-00140-z} }
Oh, Y., Zhuang, Q., Liu, L., Welp, L.R., Lau, M.C.Y., Onstott, T.C., Medvigy, D., Bruhwiler, L., Dlugokencky, E.J., Hugelius, G., D'Imperio, L. and Elberling, B.	Reduced net methane emissions due to microbial methane oxidation in a warmer Arctic [Abstract] [BibTeX]	2020	NATURE CLIMATE CHANGE Vol. 10(4), pp. 317+	article	DOI
Abstract: Methane emissions from organic-rich soils in the Arctic have been extensively studied due to their potential to increase the atmospheric methane burden as permafrost thaws(1-3). However, this methane source might have been overestimated without considering high-affinity methanotrophs (HAMs; methane-oxidizing bacteria) recently identified in Arctic mineral soils(4-7). Herein we find that integrating the dynamics of HAMs and methanogens into a biogeochemistry model(8-10) that includes permafrost soil organic carbon dynamics(3) leads to the upland methane sink doubling (similar to 5.5 Tg CH4 yr(-1)) north of 50 degrees N in simulations from 2000-2016. The increase is equivalent to at least half of the difference in net methane emissions estimated between process-based models and observation-based inversions(11,12), and the revised estimates better match site-level and regional observations(5,7,13-15). The new model projects doubled wetland methane emissions between 2017-2100 due to more accessible permafrost carbon(16-18). However, most of the increase in wetland emissions is offset by a concordant increase in the upland sink, leading to only an 18% increase in net methane emission (from 29 to 35 Tg CH4 yr(-1)). The projected net methane emissions may decrease further due to different physiological responses between HAMs and methanogens in response to increasing temperature(19,20).
BibTeX: @article{WOS:000522381600001, author = {Oh, Youmi and Zhuang, Qianlai and Liu, Licheng and Welp, Lisa R. and Lau, Maggie C. Y. and Onstott, Tullis C. and Medvigy, David and Bruhwiler, Lori and Dlugokencky, Edward J. and Hugelius, Gustaf and D'Imperio, Ludovica and Elberling, Bo}, title = {Reduced net methane emissions due to microbial methane oxidation in a warmer Arctic}, journal = {NATURE CLIMATE CHANGE}, year = {2020}, volume = {10}, number = {4}, pages = {317+}, doi = {https://doi.org/10.1038/s41558-020-0734-z} }
McCalley, C.K.	Methane-eating microbes [BibTeX]	2020	NATURE CLIMATE CHANGE Vol. 10(4), pp. 275-276	article	DOI
BibTeX: @article{WOS:000522381600003, author = {McCalley, Carmody K.}, title = {Methane-eating microbes}, journal = {NATURE CLIMATE CHANGE}, year = {2020}, volume = {10}, number = {4}, pages = {275-276}, doi = {https://doi.org/10.1038/s41558-020-0736-x} }
Koffi, E.N., Bergamaschi, P., Alkama, R. and Cescatti, A.	An observation-constrained assessment of the climate sensitivity and future trajectories of wetland methane emissions [Abstract] [BibTeX]	2020	SCIENCE ADVANCES Vol. 6(15)	article	DOI
Abstract: Wetlands are a major source of methane (CH4) and contribute between 30 and 40% to the total CH4 emissions. Wetland CH4 emissions depend on temperature, water table depth, and both the quantity and quality of organic matter. Global warming will affect these three drivers of methanogenesis, raising questions about the feedbacks between natural methane production and climate change. Until present the large-scale response of wetland CH4 emissions to climate has been investigated with land-surface models that have produced contrasting results. Here, we produce a novel global estimate of wetland methane emissions based on atmospheric inverse modeling of CH4 fluxes and observed temperature and precipitation. Our data-driven model suggests that by 2100, current emissions may increase by 50% to 80%, which is within the range of 50% and 150% reported in previous studies. This finding highlights the importance of limiting global warming below 2 degrees C to avoid substantial climate feedbacks driven by methane emissions from natural wetlands.
BibTeX: @article{WOS:000525751400014, author = {Koffi, Ernest N. and Bergamaschi, Peter and Alkama, Romain and Cescatti, Alessandro}, title = {An observation-constrained assessment of the climate sensitivity and future trajectories of wetland methane emissions}, journal = {SCIENCE ADVANCES}, year = {2020}, volume = {6}, number = {15}, doi = {https://doi.org/10.1126/sciadv.aay4444} }
Engram, M., Anthony, K.M.W., Sachs, T., Kohnert, K., Serafimovich, A., Grosse, G. and Meyer, F.J.	Remote sensing northern lake methane ebullition [Abstract] [BibTeX]	2020	NATURE CLIMATE CHANGE Vol. 10(6), pp. 511+	article	DOI
Abstract: Northern lakes are considered a major source of atmospheric methane (CH4), a potent GHG(1,2). However, large uncertainties in their emissions (7-26 Tg CH4 yr(-1); ref. (2)) arise from challenges in upscaling field data, including fluxes by ebullition (bubbling), the dominant emission pathway(2). Remote sensing of ebullition would allow detailed mapping of regional emissions but has hitherto not been developed. Here, we show that lake ebullition can be imaged using synthetic aperture radar remote sensing during ice-cover periods by exploiting the effect of ebullition on the texture of the ice-water interface. Applying this method to five Alaska regions and combining spatial remote sensing information with year-round bubble-trap flux measurements, we create ebullition-flux maps for 5,143 Alaskan lakes. Regional lake CH4 emissions, based on satellite remote sensing analyses, were lower compared to previous estimates based on upscaling from individual lakes(2,3) and were consistent with independent airborne CH4 observations. Thermokarst lakes formed by thaw of organic-rich permafrost had the highest fluxes, although lake density and lake size distributions also controlled regional emissions. This new remote sensing approach offers an opportunity to improve knowledge about Arctic CH4 fluxes and helps to explain long-standing discrepancies between estimates of CH4 emissions from atmospheric measurements and data upscaled from individual lakes. Arctic lake methane emissions, which occur primarily by ebullition, are difficult to quantify from extrapolating in situ data due to spatial and temporal variability. Remote sensing can detect ebullition, through changes in frozen lake surface properties, reducing uncertainty in emission fluxes.
BibTeX: @article{WOS:000531795100002, author = {Engram, M. and Anthony, K. M. Walter and Sachs, T. and Kohnert, K. and Serafimovich, A. and Grosse, G. and Meyer, F. J.}, title = {Remote sensing northern lake methane ebullition}, journal = {NATURE CLIMATE CHANGE}, year = {2020}, volume = {10}, number = {6}, pages = {511+}, doi = {https://doi.org/10.1038/s41558-020-0762-8} }
Matthews, E., Johnson, M.S., Genovese, V., Du, J. and Bastviken, D.	Methane emission from high latitude lakes: methane-centric lake classification and satellite-driven annual cycle of emissions [Abstract] [BibTeX]	2020	SCIENTIFIC REPORTS Vol. 10(1)	article	DOI
Abstract: Methane (CH4) is emitted from lakes by several processes: bubbles released from bottom sediments that reach the atmosphere (ebullition); spring release of CH4 trapped in bubbles in and under the ice during fall freeze (bubble release), and diffusion of CH4 from sediments to the surface. Each of these emission routes is highly variable over space and time, and episodic in the extreme, making reliable measurements difficult to carry out. However, lakes are receiving increasing interest for their important contribution to global CH4 emissions. Their area, distribution and emissions respond to interannual and longer-term climate fluctuations and close to half the world's lake area is in high northern latitudes that are experiencing rapidly-warming temperatures and lengthening thaw periods. We report on a new spatially-explicit data set of lakes >50 degrees N, classified with methane-relevant criteria. The seasonality of daily CH4 fluxes is driven with satellite observations of thaw timing and duration. We found that observed thaw seasons are 10-30% shorter than those assumed in previous studies. The area of lakes is 1,095x10(3) km(2) and total CH4 emission is 13.8-17.7 Tg CH4 year(-1): 11.2-14.4 Tg via diffusion and ebullition and 2.6-3.3 Tg from spring release of CH4 stored in bubbles in winter lake ice. This novel suite of data and methodologies provides a unique framework to model CH4 emission from lakes under current, past and future climates.
BibTeX: @article{WOS:000556875200009, author = {Matthews, E. and Johnson, Matthew S. and Genovese, V. and Du, J. and Bastviken, D.}, title = {Methane emission from high latitude lakes: methane-centric lake classification and satellite-driven annual cycle of emissions}, journal = {SCIENTIFIC REPORTS}, year = {2020}, volume = {10}, number = {1}, doi = {https://doi.org/10.1038/s41598-020-68246-1} }
Li, T., Lu, Y., Yu, L., Sun, W., Zhang, Q., Zhang, W., Wang, G., Qin, Z., Yu, L., Li, H. and Zhang, R.	Evaluation of CH4MOD(wetland) and Terrestrial Ecosystem Model (TEM) used to estimate global CH4 emissions from natural wetlands [Abstract] [BibTeX]	2020	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 13(8), pp. 3769-3788	article	DOI
Abstract: Wetlands are the largest and most uncertain natural sources of atmospheric methane (CH4). Several process-based models have been developed to quantify the magnitude and estimate spatial and temporal variations in CH4 emissions from global wetlands. Reliable models are required to estimate global wetland CH4 emissions. This study aimed to test two process-based models, CH4 MODwetland and Terrestrial Ecosystem Model (TEM), against the CH4 flux measurements of marsh, swamp, peatland and coastal wetland sites across the world; specifically, model accuracy and generality were evaluated for different wetland types and in different continents, and then the global CH4 emissions from 2000 to 2010 were estimated. Both models showed similar high correlations with the observed seasonal/annual total CH4 emissions, and the regression of the observed versus computed total seasonal/annual CH4 emissions resulted in R-2 values of 0.81 and 0.68 for CH4 MODwetland and ILM, respectively. The CH4MOD(wetland )produced accurate predictions for marshes, peatlands, swamps and coastal wetlands, with model efficiency (EF) values of 0.22, 0.52, 0.13 and 0.72, respectively. TEM produced good predictions for peatlands and swamps, with EF values of 0.69 and 0.74, respectively, but it could not accurately simulate marshes and coastal wetlands (EF < 0). There was a good correlation between the simulated CH4 fluxes and the observed values on most continents. However, CH4MOD(wetland) showed no correlation with the observed values in South America and Africa. TEM showed no correlation with the observations in Europe. The global CH4 emissions for the period 2000-2010 were estimated to be 105.31 +/- 2.72 Tg yr(-1) by CH4 MODwetland and 134.31 +/- 0.84 Tg yr(-1) by MM. Both models simulated a similar spatial distribution of CH4 emissions globally and on different continents. Marshes contribute 36 %-39 % of global CH4 emissions. Lakes/rivers and swamps are the second and third greatest contributors, respectively. Other wetland types account for only approximately 20 % of global emissions. Based on the model applicability, if we use the more accurate model, i.e., the one that performs best as evidenced by a higher model efficiency and a lower model bias, to estimate each continent and wetland type, we obtain a new assessment of 116.99-124.74 Tg yr(-1) for the global CH4 emissions for the period 2000-2010. Our results imply that performance at a global scale may conceal model uncertainty. Efforts should be made to improve model accuracy for different wetland types and regions, particularly hotspot regions, to reduce the uncertainty in global assessments.
BibTeX: @article{WOS:000566347300001, author = {Li, Tingting and Lu, Yanyu and Yu, Lingfei and Sun, Wenjuan and Zhang, Qing and Zhang, Wen and Wang, Guocheng and Qin, Zhangcai and Yu, Lijun and Li, Hailing and Zhang, Ran}, title = {Evaluation of CH4MOD(wetland) and Terrestrial Ecosystem Model (TEM) used to estimate global CH4 emissions from natural wetlands}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2020}, volume = {13}, number = {8}, pages = {3769-3788}, doi = {https://doi.org/10.5194/gmd-13-3769-2020} }
Stanevich, I., Jones, D.B.A., Strong, K., Parker, R.J., Boesch, H., Wunch, D., Notholt, J., Petri, C., Warneke, T., Sussmann, R., Schneider, M., Hase, F., Kivi, R., Deutscher, N.M., Velazco, V.A., Walker, K.A. and Deng, F.	Characterizing model errors in chemical transport modeling of methane: impact of model resolution in versions v9-02 of GEOS-Chem and v35j of its adjoint model [Abstract] [BibTeX]	2020	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 13(9), pp. 3839-3862	article	DOI
Abstract: The GEOS-Chem simulation of atmospheric CH4 was evaluated against observations from the Thermal and Near Infrared Sensor for Carbon Observations Fourier Transform Spectrometer (TANSO-FTS) on the Greenhouse Gases Observing Satellite (GOSAT), the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and the Total Carbon Column Observing Network (TCCON). We focused on the model simulations at the 4 degrees x 5 degrees and 2 degrees x 2.5 degrees horizontal resolutions for the period of February-May 2010. Compared to the GOSAT, TCCON, and ACE-FTS data, we found that the 2 degrees x 2.5 degrees model produced a better simulation of CH4, with smaller biases and a higher correlation to the independent data. We found large resolution-dependent differences such as a latitude-dependent XCH4 bias, with higher column abundances of CH4 at high latitudes and lower abundances at low latitudes at the 4 degrees x 5 degrees resolution than at 2 degrees x 2.5 degrees. We also found large differences in CH4 column abundances between the two resolutions over major source regions such as China. These differences resulted in up to 30 % differences in inferred regional CH4 emission estimates from the two model resolutions. We performed several experiments using Rn-222, Be-7, and CH4 to determine the origins of the resolution-dependent errors. The results suggested that the major source of the latitude-dependent errors is excessive mixing in the upper troposphere and lower stratosphere, including mixing at the edge of the polar vortex, which is pronounced at the 4 degrees x 5 degrees resolution. At the coarser resolution, there is weakened vertical transport in the troposphere at midlatitudes to high latitudes due to the loss of sub-grid tracer eddy mass flux in the storm track regions. The vertical air mass fluxes are calculated in the model from the degraded coarse-resolution wind fields and the model does not conserve the air mass flux between model resolutions; as a result, the low resolution does not fully capture the vertical transport. This produces significant localized discrepancies, such as much greater CH4 abundances in the lower troposphere over China at 4 degrees x 5 degrees than at 2 degrees x 2.5 degrees. Although we found that the CH4 simulation is significantly better at 2 degrees x 2.5 degrees than at 4 degrees x 5 degrees, biases may still be present at 2 degrees x 2.5 degrees resolution. Their importance, particularly in regards to inverse modeling of CH4 emissions, should be evaluated in future studies using online transport in the native general circulation model as a benchmark simulation.
BibTeX: @article{WOS:000566779800002, author = {Stanevich, Ilya and Jones, Dylan B. A. and Strong, Kimberly and Parker, Robert J. and Boesch, Hartmut and Wunch, Debra and Notholt, Justus and Petri, Christof and Warneke, Thorsten and Sussmann, Ralf and Schneider, Matthias and Hase, Frank and Kivi, Rigel and Deutscher, Nicholas M. and Velazco, Voltaire A. and Walker, Kaley A. and Deng, Feng}, title = {Characterizing model errors in chemical transport modeling of methane: impact of model resolution in versions v9-02 of GEOS-Chem and v35j of its adjoint model}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2020}, volume = {13}, number = {9}, pages = {3839-3862}, doi = {https://doi.org/10.5194/gmd-13-3839-2020} }
White, J.W.C., Allen, D., Amar, P.K., Bogner, J., Bruhwiler, L., Cooley, D., Frankenberg, C., George, F., Hanle, L., Hristov, A.H., Kebreab, E., Leytem, A., Mastalerz, M., Wofsy, S., Ravishankara, A.R., Chen, S.S., Bitz, C., Cane, M.A., Cullen, H., Dunbar, R., Emch, P., Fiore, A., Frumhoff, P., Gail, W.B., Glackin, M., Hogue, T.S., Joseph, E., Keener Jr., R.N., Kopp, R., Leung, L.R., Overpeck, J., Steiner, A., Titley, D.W., Waliser, D., Methane, C.A., Climate, B.A.S., Resources, B.A.N., Resources, B.E.S., Syst, B.E.E., Toxicology, B.E.S., Studies, D.E.L., Sci, N.A., Engn, N.A. and Med, N.A.	Improving Characterization of Anthropogenic Methane Emissions in the United States Preface [BibTeX]	2018	IMPROVING CHARACTERIZATION OF ANTHROPOGENIC METHANE EMISSIONS IN THE UNITED STATES, pp. XI+	incollection
BibTeX: @incollection{WOS:000568964900001, author = {White, James W. C. and Allen, David and Amar, Praveen K. and Bogner, Jean and Bruhwiler, Lori and Cooley, Daniel and Frankenberg, Christian and George, Fiji and Hanle, Lisa and Hristov, Alexander H. and Kebreab, Ermias and Leytem, April and Mastalerz, Maria and Wofsy, Steven and Ravishankara, A. R. and Chen, Shuyi S. and Bitz, Cecilia and Cane, Mark A. and Cullen, Heidi and Dunbar, Robert and Emch, Pamela and Fiore, Arlene and Frumhoff, Peter and Gail, William B. and Glackin, Mary and Hogue, Terri S. and Joseph, Everette and Keener, Jr., Ronald Nick and Kopp, Robert and Leung, L. Ruby and Overpeck, Jonathan and Steiner, Allison and Titley, David W. and Waliser, Duane and Comm Anthropogenic Methane and Board Atmospheric Sci Climate and Board Agr Nat Resources and Board Earth Sci Resources and Board Energy Environm Syst and Board Environm Studies Toxicology and Div Earth Life Studies and Natl Acad Sci and Natl Acad Engn and Natl Acad Med}, title = {Improving Characterization of Anthropogenic Methane Emissions in the United States Preface}, booktitle = {IMPROVING CHARACTERIZATION OF ANTHROPOGENIC METHANE EMISSIONS IN THE UNITED STATES}, year = {2018}, pages = {XI+} }
Yu, X., Millet, D.B., Wells, K.C., Henze, D.K., Cao, H., Griffis, T.J., Kort, E.A., Plant, G., Deventer, M.J., Kolka, R.K., Roman, D.T., Davis, K.J., Desai, A.R., Baier, B.C., McKain, K., Czarnetzki, A.C. and Bloom, A.A.	Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions [Abstract] [BibTeX]	2021	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 21(2), pp. 951-971	article	DOI
Abstract: We apply airborne measurements across three seasons (summer, winter and spring 2017-2018) in a multi-inversion framework to quantify methane emissions from the US Corn Belt and Upper Midwest, a key agricultural and wetland source region. Combing our seasonal results with prior fall values we find that wetlands are the largest regional methane source (32 %, 20 [16-23] Gg/d), while livestock (enteric/manure; 25 %, 15 [14-17] Gg/d) are the largest anthropogenic source. Natural gas/petroleum, waste/landfills, and coal mines collectively make up the remainder. Optimized fluxes improve model agreement with independent datasets within and beyond the study timeframe. Inversions reveal coherent and seasonally dependent spatial errors in the WetCHARTs ensemble mean wetland emissions, with an underestimate for the Prairie Pothole region but an overestimate for Great Lakes coastal wetlands. Wetland extent and emission temperature dependence have the largest influence on prediction accuracy; better representation of cou- pled soil temperature-hydrology effects is therefore needed. Our optimized regional livestock emissions agree well with the Gridded EPA estimates during spring (to within 7 %) but are similar to 25 % higher during summer and winter. Spatial analysis further shows good top-down and bottom-up agreement for beef facilities (with mainly enteric emissions) but larger (similar to 30 %) seasonal discrepancies for dairies and hog farms (with > 40 % manure emissions). Findings thus support bottom-up enteric emission estimates but suggest errors for manure; we propose that the latter reflects inadequate treatment of management factors including field application. Overall, our results confirm the importance of intensive animal agriculture for regional methane emissions, implying substantial mitigation opportunities through improved management.
BibTeX: @article{WOS:000613269200002, author = {Yu, Xueying and Millet, Dylan B. and Wells, Kelley C. and Henze, Daven K. and Cao, Hansen and Griffis, Timothy J. and Kort, Eric A. and Plant, Genevieve and Deventer, Malte J. and Kolka, Randall K. and Roman, D. Tyler and Davis, Kenneth J. and Desai, Ankur R. and Baier, Bianca C. and McKain, Kathryn and Czarnetzki, Alan C. and Bloom, A. Anthony}, title = {Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2021}, volume = {21}, number = {2}, pages = {951-971}, doi = {https://doi.org/10.5194/acp-21-951-2021} }
Bruhwiler, L., Parmentier, F.-J.W., Crill, P., Leonard, M. and Palmer I, P.	The Arctic Carbon Cycle and Its Response to Changing Climate [Abstract] [BibTeX]	2021	CURRENT CLIMATE CHANGE REPORTS Vol. 7(1), pp. 14-34	article	DOI
Abstract: Purpose of Review The Arctic has experienced the most rapid change in climate of anywhere on Earth, and these changes are certain to drive changes in the carbon budget of the Arctic as vegetation changes, soils warm, fires become more frequent, and wetlands evolve as permafrost thaws. In this study, we review the extensive evidence for Arctic climate change and effects on the carbon cycle. In addition, we re-evaluate some of the observational evidence for changing Arctic carbon budgets. Recent Findings Observations suggest a more active CO2 cycle in high northern latitude ecosystems. Evidence points to increased uptake by boreal forests and Arctic ecosystems, as well as increasing respiration, especially in autumn. However, there is currently no strong evidence of increased CH4 emissions. Long-term observations using both bottom-up (e.g., flux) and top-down (atmospheric abundance) approaches are essential for understanding changing carbon cycle budgets. Consideration of atmospheric transport is critical for interpretation of top-down observations of atmospheric carbon.
BibTeX: @article{WOS:000613966900001, author = {Bruhwiler, Lori and Parmentier, Frans-Jan W. and Crill, Patrick and Leonard, Mark and Palmer, I, Paul}, title = {The Arctic Carbon Cycle and Its Response to Changing Climate}, journal = {CURRENT CLIMATE CHANGE REPORTS}, year = {2021}, volume = {7}, number = {1}, pages = {14-34}, doi = {https://doi.org/10.1007/s40641-020-00169-5} }
Rasanen, A., Manninen, T., Korkiakoski, M., Lohila, A. and Virtanen, T.	Predicting catchment-scale methane fluxes with multi-source remote sensing [Abstract] [BibTeX]	2021	LANDSCAPE ECOLOGY Vol. 36(4), pp. 1177-1195	article	DOI
Abstract: Context Spatial patterns of CH4 fluxes can be modeled with remotely sensed data representing land cover, soil moisture and topography. Spatially extensive CH4 flux measurements conducted with portable analyzers have not been previously upscaled with remote sensing. Objectives How well can the CH4 fluxes be predicted with plot-based vegetation measures and remote sensing? How does the predictive skill of the model change when using different combinations of predictor variables? Methods We measured CH4 fluxes in 279 plots in a 12.4 km(2) peatland-forest-mosaic landscape in Pallas area, northern Finland in July 2019. We compared 20 different CH4 flux maps produced with vegetation field data and remote sensing data including Sentinel-1, Sentinel-2 and digital terrain model (DTM). Results The landscape acted as a net source of CH4 (253-502 mu g m(-2) h(-1)) and the proportion of source areas varied considerably between maps (12-50%). The amount of explained variance was high in CH4 regressions (59-76%, nRMSE 8-10%). Regressions including remote sensing predictors had better performance than regressions with plot-based vegetation predictors. The most important remote sensing predictors included VH-polarized Sentinel-1 features together with topographic wetness index and other DTM features. Spatial patterns were most accurately predicted when the landscape was divided into sinks and sources with remote sensing-based classifications, and the fluxes were modeled for sinks and sources separately. Conclusions CH4 fluxes can be predicted accurately with multi-source remote sensing in northern boreal peatland landscapes. High spatial resolution remote sensing-based maps constrain uncertainties related to CH4 fluxes and their spatial patterns.
BibTeX: @article{WOS:000616999000001, author = {Rasanen, Aleksi and Manninen, Terhikki and Korkiakoski, Mika and Lohila, Annalea and Virtanen, Tarmo}, title = {Predicting catchment-scale methane fluxes with multi-source remote sensing}, journal = {LANDSCAPE ECOLOGY}, year = {2021}, volume = {36}, number = {4}, pages = {1177-1195}, doi = {https://doi.org/10.1007/s10980-021-01194-x} }
Zeng, Z.-C., Byrne, B., Gong, F.-Y., He, Z. and Lei, L.	Correlation between paddy rice growth and satellite-observed methane column abundance does not imply causation [BibTeX]	2021	NATURE COMMUNICATIONS Vol. 12(1)	article	DOI
BibTeX: @article{WOS:000621489800005, author = {Zeng, Zhao-Cheng and Byrne, Brendan and Gong, Fang-Ying and He, Zhonghua and Lei, Liping}, title = {Correlation between paddy rice growth and satellite-observed methane column abundance does not imply causation}, journal = {NATURE COMMUNICATIONS}, year = {2021}, volume = {12}, number = {1}, doi = {https://doi.org/10.1038/s41467-021-21434-7} }
Lin, X., Zhang, W., Crippa, M., Peng, S., Han, P., Zeng, N., Yu, L. and Wang, G.	A comparative study of anthropogenic CH4 emissions over China based on the ensembles of bottom-up inventories [Abstract] [BibTeX]	2021	EARTH SYSTEM SCIENCE DATA Vol. 13(3), pp. 1073-1088	article	DOI
Abstract: Atmospheric methane (CH4) is a potent greenhouse gas that is strongly influenced by several human activities. China, as one of the major agricultural and energy production countries, contributes considerably to the global anthropogenic CH4 emissions by rice cultivation, ruminant feeding, and coal production. Understanding the characteristics of China's CH4 emissions is necessary for interpreting source contributions and for further climate change mitigation. However, the scarcity of data from some sources or years and spatially explicit information pose great challenges to completing an analysis of CH4 emissions. This study provides a comprehensive comparison of China's anthropogenic CH4 emissions by synthesizing the most current and publicly available datasets (13 inventories). The results show that anthropogenic CH4 emissions differ widely among inventories, with values ranging from 44.4-57.5 TgCH(4) yr(-1) in 2010. The discrepancy primarily resulted from the energy sector (27.3 %-60.0% of total emissions), followed by the agricultural (26.9 %-50.8 %) and waste treatment (8.1 %-21.2 %) sectors. Temporally, emissions among inventories stabilized in the 1990s but increased significantly thereafter, with annual average growth rates (AAGRs) of 2.6 %-4.0% during 2000-2010 but slower AAGRs of 0.5 %-2.2% during 2011-2015, and the emissions became relatively stable, with AAGRs of 0.3 %-0.8 %, during 2015-2019 because of the stable emissions from the energy sector (mainly coal production). Spatially, there are large differences in emissions hotspot identification among inventories, and incomplete information on emission patterns may mislead or bias mitigation efforts for CH4 emission reductions. The availability of detailed activity data for sectors or subsectors and the use of region-specific emission factors play important roles in understanding source contributions and reducing the uncertainty in bottom-up inventories. Data used in this article are available at https://doi.org/10.6084/m9.figshare.12720989 (Lin et al., 2021).
BibTeX: @article{WOS:000630176700003, author = {Lin, Xiaohui and Zhang, Wen and Crippa, Monica and Peng, Shushi and Han, Pengfei and Zeng, Ning and Yu, Lijun and Wang, Guocheng}, title = {A comparative study of anthropogenic CH4 emissions over China based on the ensembles of bottom-up inventories}, journal = {EARTH SYSTEM SCIENCE DATA}, year = {2021}, volume = {13}, number = {3}, pages = {1073-1088}, doi = {https://doi.org/10.5194/essd-13-1073-2021} }
Lu, X., Jacob, D.J., Zhang, Y., Maasakkers, J.D., Sulprizio, M.P., Shen, L., Qu, Z., Scarpelli, T.R., Nesser, H., Yantosca, R.M., Sheng, J., Andrews, A., Parker, R.J., Boesch, H., Bloom, A.A. and Ma, S.	Global methane budget and trend, 2010-2017: complementarity of inverse analyses using in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) observations [Abstract] [BibTeX]	2021	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 21(6), pp. 4637-4657	article	DOI
Abstract: We use satellite (GOSAT) and in situ (GLOBALVIEWplus CH4 ObsPack) observations of atmospheric methane in a joint global inversion of methane sources, sinks, and trends for the 2010-2017 period. The inversion is done by analytical solution to the Bayesian optimization problem, yielding closed-form estimates of information content to assess the consistency and complementarity (or redundancy) of the satellite and in situ data sets. We find that GOSAT and in situ observations are to a large extent complementary, with GOSAT providing a stronger overall constraint on the global methane distributions, but in situ observations being more important for northern midlatitudes and for relaxing global error correlations between methane emissions and the main methane sink (oxidation by OH radicals). The in-situ-only and the GOSAT-only inversions alone achieve 113 and 212 respective independent pieces of information (DOFS) for quantifying mean 2010-2017 anthropogenic emissions on 1009 global model grid elements, and respective DOFS of 67 and 122 for 2010-2017 emission trends. The joint GOSAT + in situ inversion achieves DOFS of 262 and 161 for mean emissions and trends, respectively. Thus, the in situ data increase the global information content from the GOSAT-only inversion by 20 %-30 %. The in-situ-only and GOSAT-only inversions show consistent corrections to regional methane emissions but are less consistent in optimizing the global methane budget. The joint inversion finds that oil and gas emissions in the US and Canada are underestimated relative to the values reported by these countries to the United Nations Framework Convention on Climate Change (UNFCCC) and used here as prior estimates, whereas coal emissions in China are overestimated. Wetland emissions in North America are much lower than in the mean WetCHARTs inventory used as a prior estimate. Oil and gas emissions in the US increase over the 2010-2017 period but decrease in Canada and Europe. The joint inversion yields a global methane emission of 551 Tg a(-1) averaged over 2010-2017 and a methane lifetime of 11.2 years against oxidation by tropospheric OH (86% of the methane sink).
BibTeX: @article{WOS:000634733700003, author = {Lu, Xiao and Jacob, Daniel J. and Zhang, Yuzhong and Maasakkers, Joannes D. and Sulprizio, Melissa P. and Shen, Lu and Qu, Zhen and Scarpelli, Tia R. and Nesser, Hannah and Yantosca, Robert M. and Sheng, Jianxiong and Andrews, Arlyn and Parker, Robert J. and Boesch, Hartmut and Bloom, A. Anthony and Ma, Shuang}, title = {Global methane budget and trend, 2010-2017: complementarity of inverse analyses using in situ (GLOBALVIEWplus CH4 ObsPack) and satellite (GOSAT) observations}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2021}, volume = {21}, number = {6}, pages = {4637-4657}, doi = {https://doi.org/10.5194/acp-21-4637-2021} }
Khade, V., Polavarapu, S.M., Neish, M., Houtekamer, P.L., Jones, D.B.A., Baek, S.-J., He, T.-L. and Gravel, S.	The Environment and Climate Change Canada Carbon Assimilation System (EC-CAS v1.0): demonstration with simulated CO observations [Abstract] [BibTeX]	2021	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 14(5), pp. 2525-2544	article	DOI
Abstract: In this study, we present the development of a new coupled weather and carbon monoxide (CO) data assimilation system based on the Environment and Climate Change Canada (ECCC) operational ensemble Kalman filter (EnKF). The estimated meteorological state is augmented to include CO. Variable localization is used to prevent the direct update of meteorology by the observations of the constituents and vice versa. Physical localization is used to damp spurious analysis increments far from a given observation. Perturbed surface flux fields are used to account for the uncertainty in CO due to errors in the surface fluxes. The system is demonstrated for the estimation of three-dimensional CO states using simulated observations from a variety of networks. First, a hypothetically dense, uniformly distributed observation network is used to demonstrate that the system is working. More realistic observation networks, based on surface hourly observations, and space-based observations provide a demonstration of the complementarity of the different networks and further confirm the reasonable behavior of the coupled assimilation system. Having demonstrated the ability to estimate CO distributions, this system will be extended to estimate surface fluxes in the future.
BibTeX: @article{WOS:000648544300002, author = {Khade, Vikram and Polavarapu, Saroja M. and Neish, Michael and Houtekamer, Pieter L. and Jones, Dylan B. A. and Baek, Seung-Jong and He, Tai-Long and Gravel, Sylvie}, title = {The Environment and Climate Change Canada Carbon Assimilation System (EC-CAS v1.0): demonstration with simulated CO observations}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2021}, volume = {14}, number = {5}, pages = {2525-2544}, doi = {https://doi.org/10.5194/gmd-14-2525-2021} }
Chandra, N., Patra, P.K., Bisht, J.S.H., Ito, A., Umezawa, T., Saigusa, N., Morimoto, S., Aoki, S., Janssens-Maenhout, G., Fujita, R., Takigawa, M., Watanabe, S., Saitoh, N. and Canadell, J.G.	Emissions from the Oil and Gas Sectors, Coal Mining and Ruminant Farming Drive Methane Growth over the Past Three Decades [Abstract] [BibTeX]	2021	JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN Vol. 99(2), pp. 309-337	article	DOI
Abstract: Methane (CH4) is an important greenhouse gas and plays a significant role in tropospheric and stratospheric chemistry. Despite the relevance of methane (CH4) in human-induced climate change and air pollution chemistry, there is no scientific consensus on the causes of changes in its growth rates and variability over the past three decades. We use a well-validated chemistry-transport model for simulating CH4 concentration and estimation of regional CH4 emissions by inverse modeling during 1988-2016. The control simulations are conducted using seasonally varying hydroxyl (OH) concentrations and assumed no interannual variability. Using inverse modeling of atmospheric observations, emission inventories, a wetland model, and a delta C-13-CH4 box model, we show that reductions in emissions from Europe and Russia since 1988, particularly from oil-gas exploitation and enteric fermentation, led to decreased CH4 growth rates in the 1990s. This period was followed by a quasi-stationary state of CH4 in the atmosphere during the early 2000s. CH4 resumed growth from 2007, which we attribute to increases in emissions from coal mining mainly in China and the intensification of ruminant farming in tropical regions. A sensitivity simulation using interannually varying OH shows that regional emission estimates by inversion are unaffected for the mid- and high latitude areas. We show that meridional shift in CH4 emissions toward the lower latitudes and the increase in CH4 loss by hydroxyl (OH) over the tropics finely balance out, keeping the CH4 gradients between the southern hemispheric tropical and polar sites relatively unchanged during 1988-2016. The latitudinal emissions shift is confirmed using the global distributions of the total column CH4 observations via satellite remote sensing. During our analysis period, there is no evidence of emission enhancement due to climate warming, including the boreal regions. These findings highlight key sectors for effective emission reduction strategies toward climate change mitigation.
BibTeX: @article{WOS:000661005900005, author = {Chandra, Naveen and Patra, Prabir K. and Bisht, Jagat S. H. and Ito, Akihiko and Umezawa, Taku and Saigusa, Nobuko and Morimoto, Shinji and Aoki, Shuji and Janssens-Maenhout, Greet and Fujita, Ryo and Takigawa, Masayuki and Watanabe, Shingo and Saitoh, Naoko and Canadell, Josep G.}, title = {Emissions from the Oil and Gas Sectors, Coal Mining and Ruminant Farming Drive Methane Growth over the Past Three Decades}, journal = {JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN}, year = {2021}, volume = {99}, number = {2}, pages = {309-337}, doi = {https://doi.org/10.2151/jmsj.2021-015} }
Kuhn, M.A., Varner, R.K., Bastviken, D., Crill, P., MacIntyre, S., Turetsky, M., Walter Anthony, K., McGuire, A.D. and Olefeldt, D.	BAWLD-CH4: a comprehensive dataset of methane fluxes from boreal and arctic ecosystems [Abstract] [BibTeX]	2021	EARTH SYSTEM SCIENCE DATA Vol. 13(11), pp. 5151-5189	article	DOI
Abstract: Methane (CH4) emissions from the boreal and arctic region are globally significant and highly sensitive to climate change. There is currently a wide range in estimates of high-latitude annual CH4 fluxes, where estimates based on land cover inventories and empirical CH4 flux data or process models (bottom-up approaches) generally are greater than atmospheric inversions (top-down approaches). A limitation of bottom-up approaches has been the lack of harmonization between inventories of site-level CH4 flux data and the land cover classes present in high-latitude spatial datasets. Here we present a comprehensive dataset of small-scale, surface CH4 flux data from 540 terrestrial sites (wetland and non-wetland) and 1247 aquatic sites (lakes and ponds), compiled from 189 studies. The Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4) was constructed in parallel with a compatible land cover dataset, sharing the same land cover classes to enable refined bottom-up assessments. BAWLD-CH4 includes information on site-level CH4 fluxes but also on study design (measurement method, timing, and frequency) and site characteristics (vegetation, climate, hydrology, soil, and sediment types, permafrost conditions, lake size and depth, and our determination of land cover class). The different land cover classes had distinct CH4 fluxes, resulting from definitions that were either based on or co-varied with key environmental controls. Fluxes of CH4 from terrestrial ecosystems were primarily influenced by water table position, soil temperature, and vegetation composition, while CH4 fluxes from aquatic ecosystems were primarily influenced by water temperature, lake size, and lake genesis. Models could explain more of the between-site variability in CH4 fluxes for terrestrial than aquatic ecosystems, likely due to both less precise assessments of lake CH4 fluxes and fewer consistently reported lake site characteristics. Analysis of BAWLD-CH4 identified both land cover classes and regions within the boreal and arctic domain, where future studies should be focused, alongside methodological approaches. Overall, BAWLD-CH4 provides a comprehensive dataset of CH4 emissions from high-latitude ecosystems that are useful for identifying research opportunities, for comparison against new field data, and model parameterization or validation.
BibTeX: @article{WOS:000715853800001, author = {Kuhn, McKenzie A. and Varner, Ruth K. and Bastviken, David and Crill, Patrick and MacIntyre, Sally and Turetsky, Merritt and Walter Anthony, Katey and McGuire, Anthony D. and Olefeldt, David}, title = {BAWLD-CH4: a comprehensive dataset of methane fluxes from boreal and arctic ecosystems}, journal = {EARTH SYSTEM SCIENCE DATA}, year = {2021}, volume = {13}, number = {11}, pages = {5151-5189}, doi = {https://doi.org/10.5194/essd-13-5151-2021} }
Li, L. and Xue, B.	Methane emissions from northern lakes under climate change: a review [Abstract] [BibTeX]	2021	SN APPLIED SCIENCES Vol. 3(12)	article	DOI
Abstract: Northern lakes are important sources of CH4 in the atmosphere under the background of permafrost thaw and winter warming. We synthesize studies on thermokarst lakes, including various carbon sources for CH4 emission and the influence of thermokarst drainage on carbon emission, to show the evasion potential of ancient carbon that stored in the permafrost and CH4 emission dynamics along with thermokarst lake evolution. Besides, we discuss the lake CH4 dynamics in seasonally ice-covered lakes, especially for under-ice CH4 accumulation and emission during spring ice melt and the possible influential factors for CH4 emission in ice-melt period. We summarize the latest findings and point out that further research should be conducted to investigate the possibility of abundant ancient carbon emission from thermokarst lakes under climate warming and quantify the contribution of ice-melt CH4 emission from northern lakes on a large scale.
BibTeX: @article{WOS:000722225200003, author = {Li, Lingling and Xue, Bin}, title = {Methane emissions from northern lakes under climate change: a review}, journal = {SN APPLIED SCIENCES}, year = {2021}, volume = {3}, number = {12}, doi = {https://doi.org/10.1007/s42452-021-04869-x} }
Li, L., Lei, L., Song, H., Zeng, Z. and He, Z.	Spatiotemporal Geostatistical Analysis and Global Mapping of CH4 Columns from GOSAT Observations [Abstract] [BibTeX]	2022	REMOTE SENSING Vol. 14(3)	article	DOI
Abstract: Methane (CH4) is one of the most important greenhouse gases causing the global warming effect. The mapping data of atmospheric CH4 concentrations in space and time can help us better to understand the characteristics and driving factors of CH4 variation as to support the actions of CH4 emission reduction for preventing the continuous increase of atmospheric CH4 concentrations. In this study, we applied a spatiotemporal geostatistical analysis and prediction to develop an approach to generate the mapping CH4 dataset (Mapping-XCH4) in 1 degrees grid and three days globally using column averaged dry air mole fraction of CH4 (XCH4) data derived from observations of the Greenhouse Gases Observing Satellite (GOSAT) from April 2009 to April 2020. Cross-validation for the spatiotemporal geostatistical predictions showed better correlation coefficient of 0.97 and a mean absolute prediction error of 7.66 ppb. The standard deviation is 11.42 ppb when comparing the Mapping-XCH4 data with the ground measurements from the total carbon column observing network (TCCON). Moreover, we assessed the performance of this Mapping-XCH4 dataset by comparing with the XCH4 simulations from the CarbonTracker model and primarily investigating the variations of XCH4 from April 2009 to April 2020. The results showed that the mean annual increase in XCH4 was 7.5 ppb/yr derived from Mapping-XCH4, which was slightly greater than 7.3 ppb/yr from the ground observational network during the past 10 years from 2010. XCH4 is larger in South Asia and eastern China than in the other regions, which agrees with the XCH4 simulations. The Mapping-XCH4 shows a significant linear relationship and a correlation coefficient of determination (R-2) of 0.66, with EDGAR emission inventories over Monsoon Asia. Moreover, we found that Mapping-XCH4 could detect the reduction of XCH4 in the period of lockdown from January to April 2020 in China, likely due to the COVID-19 pandemic. In conclusion, we can apply GOSAT observations over a long period from 2009 to 2020 to generate a spatiotemporally continuous dataset globally using geostatistical analysis. This long-term Mpping-XCH4 dataset has great potential for understanding the spatiotemporal variations of CH4 concentrations induced by natural processes and anthropogenic emissions at a global and regional scale.
BibTeX: @article{WOS:000759879400001, author = {Li, Luman and Lei, Liping and Song, Hao and Zeng, Zhaocheng and He, Zhonghua}, title = {Spatiotemporal Geostatistical Analysis and Global Mapping of CH4 Columns from GOSAT Observations}, journal = {REMOTE SENSING}, year = {2022}, volume = {14}, number = {3}, doi = {https://doi.org/10.3390/rs14030654} }
Tenkanen, M., Tsuruta, A., Rautiainen, K., Kangasaho, V., Ellul, R. and Aalto, T.	Utilizing Earth Observations of Soil Freeze/Thaw Data and Atmospheric Concentrations to Estimate Cold Season Methane Emissions in the Northern High Latitudes [Abstract] [BibTeX]	2021	REMOTE SENSING Vol. 13(24)	article	DOI
Abstract: The northern wetland methane emission estimates have large uncertainties. Inversion models are a qualified method to estimate the methane fluxes and emissions in northern latitudes but when atmospheric observations are sparse, the models are only as good as their a priori estimates. Thus, improving a priori estimates is a competent way to reduce uncertainties and enhance emission estimates in the sparsely sampled regions. Here, we use a novel way to integrate remote sensing soil freeze/thaw (F/T) status from SMOS satellite to better capture the seasonality of methane emissions in the northern high latitude. The SMOS F/T data provide daily information of soil freezing state in the northern latitudes, and in this study, the data is used to define the cold season in the high latitudes and, thus, improve our knowledge of the seasonal cycle of biospheric methane fluxes. The SMOS F/T data is implemented to LPX-Bern DYPTOP model estimates and the modified fluxes are used as a biospheric a priori in the inversion model CarbonTracker Europe-CH4. The implementation of the SMOS F/T soil state is shown to be beneficial in improving the inversion model's cold season biospheric flux estimates. Our results show that cold season biospheric CH4 emissions in northern high latitudes are approximately 0.60 Tg lower than previously estimated, which corresponds to 17% reduction in the cold season biospheric emissions. This reduction is partly compensated by increased anthropogenic emissions in the same area (0.23 Tg), and the results also indicates that the anthropogenic emissions could have even larger contribution in cold season than estimated here.
BibTeX: @article{WOS:000771728900014, author = {Tenkanen, Maria and Tsuruta, Aki and Rautiainen, Kimmo and Kangasaho, Vilma and Ellul, Raymond and Aalto, Tuula}, title = {Utilizing Earth Observations of Soil Freeze/Thaw Data and Atmospheric Concentrations to Estimate Cold Season Methane Emissions in the Northern High Latitudes}, journal = {REMOTE SENSING}, year = {2021}, volume = {13}, number = {24}, doi = {https://doi.org/10.3390/rs13245059} }
van Huissteden, J.	Methane and Biogenic Volatile Organic Compound Emissions in Eastern Siberia [BibTeX]	2019	Vol. 236WATER-CARBON DYNAMICS IN EASTERN SIBERIA, pp. 101-134	incollection	DOI
BibTeX: @incollection{WOS:000778471200006, author = {van Huissteden, Jacobus}, title = {Methane and Biogenic Volatile Organic Compound Emissions in Eastern Siberia}, booktitle = {WATER-CARBON DYNAMICS IN EASTERN SIBERIA}, year = {2019}, volume = {236}, pages = {101-134}, doi = {https://doi.org/10.1007/978-981-13-6317-7%5C_5} }
Salmon, E., Jegou, F., Guenet, B., Jourdain, L., Qiu, C., Bastrikov, V., Guimbaud, C., Zhu, D., Ciais, P., Peylin, P., Gogo, S., Laggoun-Defarge, F., Aurela, M., Bret-Harte, M.S., Chen, J., Chojnicki, B.H., Chu, H., Edgar, C.W., Euskirchen, E.S., Flanagan, L.B., Fortuniak, K., Holl, D., Klatt, J., Kolle, O., Kowalska, N., Kutzbach, L., Lohila, A., Merbold, L., Pawlak, W., Sachs, T. and Ziemblinska, K.	Assessing methane emissions for northern peatlands in ORCHIDEE-PEAT revision 7020 [Abstract] [BibTeX]	2022	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 15(7), pp. 2813-2838	article	DOI
Abstract: In the global methane budget, the largest natural source is attributed to wetlands, which encompass all ecosystems composed of waterlogged or inundated ground, capable of methane production. Among them, northern peatlands that store large amounts of soil organic carbon have been functioning, since the end of the last glaciation period, as long-term sources of methane (CH4) and are one of the most significant methane sources among wetlands. To reduce uncertainty of quantifying methane flux in the global methane budget, it is of significance to understand the underlying processes for methane production and fluxes in northern peatlands. A methane model that features methane production and transport by plants, ebullition process and diffusion in soil, oxidation to CO2, and CH4 fluxes to the atmosphere has been embedded in the ORCHIDEE-PEAT land surface model that includes an explicit representation of northern peatlands. ORCHIDEE-PCH4 was calibrated and evaluated on 14 peatland sites distributed on both the Eurasian and American continents in the northern boreal and temperate regions. Data assimilation approaches were employed to optimized parameters at each site and at all sites simultaneously. Results show that methanogenesis is sensitive to temperature and substrate availability over the top 75 cm of soil depth. Methane emissions estimated using single site optimization (SSO) of model parameters are underestimated by 9 g CH4 m(-2) yr(-1) on average (i.e., 50 % higher than the site average of yearly methane emissions). While using the multi-site optimization (MSO), methane emissions are overestimated by 5 g CH4 m(-2) yr(-1) on average across all investigated sites (i.e., 37 % lower than the site average of yearly methane emissions).
BibTeX: @article{WOS:000792361900001, author = {Salmon, Elodie and Jegou, Fabrice and Guenet, Bertrand and Jourdain, Line and Qiu, Chunjing and Bastrikov, Vladislav and Guimbaud, Christophe and Zhu, Dan and Ciais, Philippe and Peylin, Philippe and Gogo, Sebastien and Laggoun-Defarge, Fatima and Aurela, Mika and Bret-Harte, M. Syndonia and Chen, Jiquan and Chojnicki, Bogdan H. and Chu, Housen and Edgar, Colin W. and Euskirchen, Eugenie S. and Flanagan, Lawrence B. and Fortuniak, Krzysztof and Holl, David and Klatt, Janina and Kolle, Olaf and Kowalska, Natalia and Kutzbach, Lars and Lohila, Annalea and Merbold, Lutz and Pawlak, Wlodzimierz and Sachs, Torsten and Ziemblinska, Klaudia}, title = {Assessing methane emissions for northern peatlands in ORCHIDEE-PEAT revision 7020}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2022}, volume = {15}, number = {7}, pages = {2813-2838}, doi = {https://doi.org/10.5194/gmd-15-2813-2022} }
Barton-Grimley, R.A., Nehrir, A.R., Kooi, S.A., Collins, J.E., Harper, D.B., Notari, A., Lee, J., DiGangi, J.P., Choi, Y. and Davis, K.J.	Evaluation of the High Altitude Lidar Observatory (HALO) methane retrievals during the summer 2019 ACT-America campaign [Abstract] [BibTeX]	2022	ATMOSPHERIC MEASUREMENT TECHNIQUES Vol. 15(15), pp. 4623-4650	article	DOI
Abstract: The NASA Langley Research Center High Altitude Lidar Observatory (HALO) is a multi-functional and modular lidar developed to address the observational needs of NASA's weather, climate, carbon cycle, and atmospheric composition focus areas. HALO measures atmospheric H2O mixing ratios, CH4 mole fractions, and aerosol/cloud optical properties using the differential absorption lidar (DIAL) and high-spectral-resolution lidar (HSRL) techniques. In 2019 HALO participated in the NASA Atmospheric Carbon and Transport - America campaign on board the NASA C-130 to complement a suite of greenhouse gas in situ sensors and provide, for the first time, simultaneous measurements of column CH4 and aerosol/cloud profiles. HALO operated in 18 of 19 science flights where the DIAL and integrated path differential absorption (IPDA) lidar techniques at 1645 nm were used for column and multi-layer measurements of CH4 mole fractions, and the HSRL and backscatter techniques were used at 532 and 1064 nm, respectively, for retrievals of aerosol backscatter, extinction, depolarization, and mixing layer heights. In this paper we present HALO's measurement theory for the retrievals of column and multi-layer XCH4, retrieval accuracy, and precision including methods for bias correction and a comprehensive total column XCH4 validation comparison to in situ observations. Comparisons of HALO XCH4 to in situ-derived XCH4, collected during spiral ascents and descents, indicate a mean difference of 2.54 ppb and standard deviation (SD) of the differences of 16.66 ppb when employing 15 s along-track averaging (< 3 km). A high correlation coefficient of R = 0.9058 was observed for the 11 in situ spiral comparisons. Column XCH4 measured by HALO over regional scales covered by the ACT-America campaign is compared against in situ CH4 measurements carried out within the planetary boundary layer (PBL) from both the C-130 and B200 aircraft. Favorable correlation between the in situ point measurements within the PBL and the remote column measurements from HALO elucidates the sensitivity of a column-integrating lidar to CH4 variability within the PBL, where surface fluxes dominate the signal. Novel capabilities for CH4 profiling in regions of clear air using the DIAL technique are presented and validated for the first time. Additionally, profiling of CH4 is used to apportion the PBL absorption from the total column and is compared to previously reported IPDA cloud slicing techniques that estimate PBL columns using strong echoes from fair weather cumulus. The analysis presented here points towards HALO's ability to retrieve accurate and precise CH4 columns with the prospects for future multilayer profiling in support of future suborbital campaigns.
BibTeX: @article{WOS:000840451700001, author = {Barton-Grimley, Rory A. and Nehrir, Amin R. and Kooi, Susan A. and Collins, James E. and Harper, David B. and Notari, Anthony and Lee, Joseph and DiGangi, Joshua P. and Choi, Yonghoon and Davis, Kenneth J.}, title = {Evaluation of the High Altitude Lidar Observatory (HALO) methane retrievals during the summer 2019 ACT-America campaign}, journal = {ATMOSPHERIC MEASUREMENT TECHNIQUES}, year = {2022}, volume = {15}, number = {15}, pages = {4623-4650}, doi = {https://doi.org/10.5194/amt-15-4623-2022} }
Yang, T., He, Q., Jiang, J., Sheng, L., Jiang, H. and He, C.	Impact of Water Table on Methane Emission Dynamics in Terrestrial Wetlands and Implications on Strategies for Wetland Management and Restoration [Abstract] [BibTeX]	2022	WETLANDS Vol. 42(8)	article	DOI
Abstract: Methane is a potent greenhouse gas. Wetlands are considered as significant sources of methane emission, prompting the need to understand determinants of methane flux in these critical ecosystems. The importance of the water table in methane emission has been noted in terrestrial wetlands; however, the role of the water table in methane emission remains to be clarified in order for the development of strategies to mitigate methane emission from wetland ecosystems. This review examines the current literature on factors influencing methane emission in terrestrial wetlands. The water table was illustrated as an overriding factor that controls both methane generation and consumption. The contribution of other main factors, including substrate characteristics, wetland plants and temperature, to methane emission was also discussed. Building upon the growing understanding of processes underlying methane emission, strategies centered around the control of water table was proposed to minimize methane emission in wetland management and restoration efforts to maximize the ecological value of wetlands.
BibTeX: @article{WOS:000893918900003, author = {Yang, Tao and He, Qiang and Jiang, Jing and Sheng, Lianxi and Jiang, Haibo and He, Chunguang}, title = {Impact of Water Table on Methane Emission Dynamics in Terrestrial Wetlands and Implications on Strategies for Wetland Management and Restoration}, journal = {WETLANDS}, year = {2022}, volume = {42}, number = {8}, doi = {https://doi.org/10.1007/s13157-022-01634-7} }
Wang, H., Zhao, Z., Wu, Y. and Luo, X.	B-Spline Method for Spatio-Temporal Inverse Model [Abstract] [BibTeX]	2022	JOURNAL OF SYSTEMS SCIENCE & COMPLEXITY Vol. 35(6), pp. 2336-2360	article	DOI
Abstract: Inverse models can be used to estimate surface fluxes in terms of the observed atmospheric concentration measurement data. This paper proposes a new nonparametric spatio-temporal inverse model and provides the global expressions for the estimates by employing the B-spline method. The authors establish the asymptotic normality of the estimators under mild conditions. The authors also conduct numerical studies to evaluate the finite sample performance of the proposed methodologies. Finally, the authors apply the method to anthropogenic carbon dioxide (CO2) emission data from different provinces of Canada to illustrate the validity of the proposed techniques.
BibTeX: @article{WOS:000905679100017, author = {Wang, Hongxia and Zhao, Zihan and Wu, Yuehua and Luo, Xuehong}, title = {B-Spline Method for Spatio-Temporal Inverse Model}, journal = {JOURNAL OF SYSTEMS SCIENCE & COMPLEXITY}, year = {2022}, volume = {35}, number = {6}, pages = {2336-2360}, doi = {https://doi.org/10.1007/s11424-022-1206-5} }
Watts, J.D., Farina, M., Kimball, J.S., Schiferl, L.D., Liu, Z., Arndt, K.A., Zona, D., Ballantyne, A., Euskirchen, E.S., Parmentier, F.-J.W., Helbig, M., Sonnentag, O., Tagesson, T., Rinne, J., Ikawa, H., Ueyama, M., Kobayashi, H., Sachs, T., Nadeau, D.F., Kochendorfer, J., Jackowicz-Korczynski, M., Virkkala, A., Aurela, M., Commane, R., Byrne, B., Birch, L., Johnson, M.S., Madani, N., Rogers, B., Du, J., Endsley, A., Savage, K., Poulter, B., Zhang, Z., Bruhwiler, L.M., Miller, C.E., Goetz, S. and Oechel, W.C.	Carbon uptake in Eurasian boreal forests dominates the high-latitude net ecosystem carbon budget [Abstract] [BibTeX]	2023	GLOBAL CHANGE BIOLOGY Vol. 29(7), pp. 1870-1889	article	DOI
Abstract: Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003-2015) vegetation gross primary productivity (GPP), ecosystem respiration (R-eco), net ecosystem CO2 exchange (NEE; R-eco - GPP), and terrestrial methane (CH4) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km(2) flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of -850 Tg CO2-C year(-1). Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4-C year(-1). Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change.
BibTeX: @article{WOS:000915387000001, author = {Watts, Jennifer D. and Farina, Mary and Kimball, John S. and Schiferl, Luke D. and Liu, Zhihua and Arndt, Kyle A. and Zona, Donatella and Ballantyne, Ashley and Euskirchen, Eugenie S. and Parmentier, Frans-Jan W. and Helbig, Manuel and Sonnentag, Oliver and Tagesson, Torbern and Rinne, Janne and Ikawa, Hiroki and Ueyama, Masahito and Kobayashi, Hideki and Sachs, Torsten and Nadeau, Daniel F. and Kochendorfer, John and Jackowicz-Korczynski, Marcin and Virkkala, Anna and Aurela, Mika and Commane, Roisin and Byrne, Brendan and Birch, Leah and Johnson, Matthew S. and Madani, Nima and Rogers, Brendan and Du, Jinyang and Endsley, Arthur and Savage, Kathleen and Poulter, Ben and Zhang, Zhen and Bruhwiler, Lori M. and Miller, Charles E. and Goetz, Scott and Oechel, Walter C.}, title = {Carbon uptake in Eurasian boreal forests dominates the high-latitude net ecosystem carbon budget}, journal = {GLOBAL CHANGE BIOLOGY}, year = {2023}, volume = {29}, number = {7}, pages = {1870-1889}, doi = {https://doi.org/10.1111/gcb.16553} }
Yu, X., Millet, D.B., Henze, D.K., Turner, A.J., Delgado, A.L., Bloom, A.A. and Sheng, J.	A high-resolution satellite-based map of global methane emissions reveals missing wetland, fossil fuel, and monsoon sources [Abstract] [BibTeX]	2023	ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 23(5), pp. 3325-3346	article	DOI
Abstract: We interpret space-borne observations from the TROPOspheric Monitoring Instrument (TROPOMI) in a multi-inversion framework to characterize the 2018-2019 global methane budget. Evaluation of the inverse solutions indicates that simultaneous source + sink optimization using methane observations alone remains an ill-posed problem - even with the dense TROPOMI sampling coverage. Employing remote carbon monoxide (CO) and hydroxyl radical (OH) observations with independent methane measurements to distinguish between candidate solutions, we infer from TROPOMI a global methane source of 587 (586-589) Tg yr(-1) and sink of 571 Tg yr(-1) for our analysis period. We apply a new downscaling method to map the derived monthly emissions to 0.1 degrees x 0.1 degrees resolution, using the results to uncover key gaps in the prior methane budget. The TROPOMI data point to an underestimate of tropical wetland emissions (a posteriori increase of +13 % [6 %-25 %] or 20 [7-25] Tg yr(-1)), with adjustments following regional hydrology. Some simple wetland parameterizations represent these patterns as accurately as more sophisticated process-based models. Emissions from fossil fuel activities are strongly underestimated over the Middle East (+5 [2-6] Tg yr(-1) a posteriori increase) and over Venezuela. The TROPOMI observations also reveal many fossil fuel emission hotspots missing from the prior inventory, including over Mexico, Oman, Yemen, Turkmenistan, Iran, Iraq, Libya, and Algeria. Agricultural methane sources are underestimated in India, Brazil, the California Central Valley, and Asia. Overall, anthropogenic sources worldwide are increased by +19 [11-31] Tg yr(-1) over the prior estimate. More than 45 % of this adjustment occurs over India and Southeast Asia during the summer monsoon (+8.5 [3.1-10.7] Tg in July-October), likely due to rainfall-enhanced emissions from rice, manure, and landfills/sewers, which increase during this season along with the natural wetland source.
BibTeX: @article{WOS:000953028200001, author = {Yu, Xueying and Millet, Dylan B. and Henze, Daven K. and Turner, Alexander J. and Delgado, Alba Lorente and Bloom, A. Anthony and Sheng, Jianxiong}, title = {A high-resolution satellite-based map of global methane emissions reveals missing wetland, fossil fuel, and monsoon sources}, journal = {ATMOSPHERIC CHEMISTRY AND PHYSICS}, year = {2023}, volume = {23}, number = {5}, pages = {3325-3346}, doi = {https://doi.org/10.5194/acp-23-3325-2023} }
Song, W., Yao, W., Zhao, Y., Wang, M., Chen, R., Zhu, Z., Gao, Z., Li, C., Liang, M. and Yu, D.	City-Level CH4 Emissions from Anthropogenic Sources and Its Environmental Behaviors in China's Cold Cities [Abstract] [BibTeX]	2023	ATMOSPHERE Vol. 14(3)	article	DOI
Abstract: Distinguished features of cities influence the characteristics of CH4 emissions. A city-level emission inventory represents the characteristics of CH4 on a smaller scale, according to the special factors in each city. A city-level emission inventory was established to reveal the characteristics and source profile of CH4 emissions in the coldest province, which is a typical provincial cold region in northeast China. The dominant sources were identified for targeted cities. Rice cultivation, coal mining, oil and gas exploitation, and livestock are the dominant emission sectors. Emissions from other sectors, including wastewater disposal, biomass burning, landfill, etc. were also estimated. The provincial CH4 emissions increased gradually from 2003 to 2012, up to 2993.26 Gg with an annual increase rate of 2.85%; the emissions were 2740.63 in 2020. The emissions of CH4 in Harbin, Daqing, Jiamusi, and Hegang cities were higher than in the other nine cities, which were 337.23 Gg, 330.01 Gg, 328.55 Gg, and 307.42 Gg in 2020, respectively. Agriculture, including the rice cultivation, livestock, and biomass burning sectors contributed to 51.24-62.12% of total emissions, and the contributions increased gradually. Coal mining, oil and gas exploration, and fossil fuel combustion are energy-related sources, which contributed up to 37.91% of the total emissions, and the proportion kept decreasing to 23.87% in 2020. Furthermore, meteorological factors are especially relevant to the region, by which the differences of ambient temperature are over 60 degrees C (+/- 30 degrees C). In the summer, CH4 emissions from the rice cultivation, biomass burning, livestock, and landfill sectors are obviously distinct from the heating period (winter), while few differences in CH4 emissions are found from wastewater disposal and the fossil fuel production sectors.
BibTeX: @article{WOS:000954626500001, author = {Song, Weiwei and Yao, Wanying and Zhao, Yixuan and Wang, Mengying and Chen, Ruihan and Zhu, Zhiyu and Gao, Zhi and Li, Chunhui and Liang, Miao and Yu, Dajiang}, title = {City-Level CH4 Emissions from Anthropogenic Sources and Its Environmental Behaviors in China's Cold Cities}, journal = {ATMOSPHERE}, year = {2023}, volume = {14}, number = {3}, doi = {https://doi.org/10.3390/atmos14030535} }
Liu, X. and Zhuang, Q.	Methane emissions from Arctic landscapes during 2000-2015: an analysis withland and lake biogeochemistry models [Abstract] [BibTeX]	2023	BIOGEOSCIENCES Vol. 20(6), pp. 1181-1193	article	DOI
Abstract: Wetlands and freshwater bodies (mainly lakes) are the largest natural sources of the greenhouse gas CH4 to the atmosphere. Great efforts have been made to quantify these source emissions and their uncertainties. Previous research suggests that there might be significant uncertainties coming from ``double accounting'' emissions from freshwater bodies and wetlands. Here we quantify the methane emissions from both land and freshwater bodies in the pan-Arctic with two process-based biogeochemistry models by minimizing the double accounting at the landscape scale. Two non-overlapping dynamic areal change datasets are used to drive the models. We estimate that the total methane emissions from the pan-Arctic are 36.46 +/- 1.02 Tg CH4 yr(-1)during 2000-2015, of which wetlands and freshwater bodies are 21.69 +/- 0.59 Tg CH4 yr(-1) and 14.76 +/- 0.44 Tg CH4 yr(-1), respectively. Our estimation narrows the difference between previous bottom-up (53.9 Tg CH4 yr(-1)) and top-down (29 Tg CH4 yr(-1)) estimates. Our correlation analysis shows that air temperature is the most important driver for methane emissions of inland water systems. Wetland emissions are also significantly affected by vapor pressure, while lake emissions are more influenced by precipitation and landscape areal changes. Sensitivity tests indicate that pan-Arctic lake CH4 emissions were highly influenced by air temperature but less by lake sediment carbon increase.
BibTeX: @article{WOS:000959121900001, author = {Liu, Xiangyu and Zhuang, Qianlai}, title = {Methane emissions from Arctic landscapes during 2000-2015: an analysis withland and lake biogeochemistry models}, journal = {BIOGEOSCIENCES}, year = {2023}, volume = {20}, number = {6}, pages = {1181-1193}, doi = {https://doi.org/10.5194/bg-20-1181-2023} }
Bisht, J.S.H., Patra, P.K., Takigawa, M., Sekiya, T., Kanaya, Y., Saitoh, N. and Miyazaki, K.	Estimation of CH4 emission based on an advanced 4D-LETKF assimilation system [Abstract] [BibTeX]	2023	GEOSCIENTIFIC MODEL DEVELOPMENT Vol. 16(6), pp. 1823-1838	article	DOI
Abstract: Methane (CH4) is the second major greenhouse gas after carbon dioxide (CO2) which has substantially increased during recent decades in the atmosphere, raising serious sustainability and climate change issues. Here, we develop a data assimilation system for in situ and column-averaged concentrations using a local ensemble transform Kalman filter (LETKF) to estimate surface emissions of CH4. The data assimilation performance is tested and optimized based on idealized settings using observation system simulation experiments (OSSEs), where a known surface emission distribution (the truth) is retrieved from synthetic observations. We tested three covariance inflation methods to avoid covariance underestimation in the emission estimates, namely fixed multiplicative (FM), relaxation-to-prior spread (RTPS), and adaptive multiplicative. First, we assimilate the synthetic observations at every grid point at the surface level. In such a case of dense observational data, the normalized root mean square error (RMSE) in the analyses over global land regions is smaller by 10 %-15 % in the case of RTPS covariance inflation method compared to FM. We have shown that integrated estimated flux seasonal cycles over 15 regions using RTPS inflation are in reasonable agreement between true and estimated flux, with 0.04 global normalized annual mean bias. We then assimilated the column-averaged CH4 concentration by sampling the model simulations at Greenhouse Gases Observing Satellite (GOSAT) observation locations and time for another OSSE. Similar to the case of dense observational data, the RTPS covariance inflation method performs better than FM for GOSAT synthetic observation in terms of normalized RMSE (2 %-3 %) and integrated flux estimation comparison with the true flux. The annual mean averaged normalized RMSE (normalized mean bias) in LETKF CH4 flux estimation in the case of RTPS and FM covariance inflation is found to be 0.59 (0.18) and 0.61 (0.23), respectively. The ?(2) test performed for GOSAT synthetic observations assimilation suggests high underestimation of background error covariance in both RTPS and FM covariance inflation methods; however, the underestimation is much higher (>100 % always) for FM compared to RTPS covariance inflation method.
BibTeX: @article{WOS:000961064700001, author = {Bisht, Jagat S. H. and Patra, Prabir K. and Takigawa, Masayuki and Sekiya, Takashi and Kanaya, Yugo and Saitoh, Naoko and Miyazaki, Kazuyuki}, title = {Estimation of CH4 emission based on an advanced 4D-LETKF assimilation system}, journal = {GEOSCIENTIFIC MODEL DEVELOPMENT}, year = {2023}, volume = {16}, number = {6}, pages = {1823-1838}, doi = {https://doi.org/10.5194/gmd-16-1823-2023} }
Ludwig, S.M., Natali, S.M., Schade, J.D., Powell, M., Fiske, G., Schiferl, L.D. and Commane, R.	Scaling waterbody carbon dioxide and methane fluxes in the arctic using an integrated terrestrial-aquatic approach [Abstract] [BibTeX]	2023	ENVIRONMENTAL RESEARCH LETTERS Vol. 18(6)	article	DOI
Abstract: In the Arctic waterbodies are abundant and rapid thaw of permafrost is destabilizing the carbon cycle and changing hydrology. It is particularly important to quantify and accurately scale aquatic carbon emissions in arctic ecosystems. Recently available high-resolution remote sensing datasets capture the physical characteristics of arctic landscapes at unprecedented spatial resolution. We demonstrate how machine learning models can capitalize on these spatial datasets to greatly improve accuracy when scaling waterbody CO2 and CH4 fluxes across the YK Delta of south-west AK. We found that waterbody size and contour were strong predictors for aquatic CO2 emissions, attributing greater than two-thirds of the influence to the scaling model. Small ponds (<0.001 km(2)) were hotspots of emissions, contributing fluxes several times their relative area, but were less than 5% of the total carbon budget. Small to medium lakes (0.001-0.1 km(2)) contributed the majority of carbon emissions from waterbodies. Waterbody CH4 emissions were predicted by a combination of wetland landcover and related drivers, as well as watershed hydrology, and waterbody surface reflectance related to chromophoric dissolved organic matter. When compared to our machine learning approach, traditional scaling methods that did not account for relevant landscape characteristics overestimated waterbody CO2 and CH4 emissions by 26%-79% and 8%-53% respectively. This study demonstrates the importance of an integrated terrestrial-aquatic approach to improving estimates and uncertainty when scaling C emissions in the arctic.
BibTeX: @article{WOS:000990896500001, author = {Ludwig, Sarah M. and Natali, Susan M. and Schade, John D. and Powell, Margaret and Fiske, Greg and Schiferl, Luke D. and Commane, Roisin}, title = {Scaling waterbody carbon dioxide and methane fluxes in the arctic using an integrated terrestrial-aquatic approach}, journal = {ENVIRONMENTAL RESEARCH LETTERS}, year = {2023}, volume = {18}, number = {6}, doi = {https://doi.org/10.1088/1748-9326/acd467} }
Zhou, L., Warner, J., Nalli, N.R., Wei, Z., Oh, Y., Bruhwiler, L., Liu, X., Divakarla, M., Pryor, K., Kalluri, S. and Goldberg, M.D.	Spatiotemporal Variability of Global Atmospheric Methane Observed from Two Decades of Satellite Hyperspectral Infrared Sounders [Abstract] [BibTeX]	2023	REMOTE SENSING Vol. 15(12)	article	DOI
Abstract: Methane (CH4) is the second most significant contributor to climate change after carbon dioxide (CO2), accounting for approximately 20% of the contributions from all well-mixed greenhouse gases. Understanding the spatiotemporal distributions and the relevant long-term trends is crucial to identifying the sources, sinks, and impacts on climate. Hyperspectral thermal infrared (TIR) sounders, including the Atmospheric Infrared Sounder (AIRS), the Cross-track Infrared Sounder (CrIS), and the Infrared Atmospheric Sounding Interferometer (IASI), have been used to measure global CH4 concentrations since 2002. This study analyzed nearly 20 years of data from AIRS and CrIS and confirmed a significant increase in CH4 concentrations in the mid-upper troposphere (around 400 hPa) from 2003 to 2020, with a total increase of approximately 85 ppb, representing a +4.8% increase in 18 years. The rate of increase was derived using global satellite TIR measurements, which are consistent with in situ measurements, indicating a steady increase starting in 2007 and becoming stronger in 2014. The study also compared CH4 concentrations derived from the AIRS and CrIS against ground-based measurements from NOAA Global Monitoring Laboratory (GML) and found phase shifts in the seasonal cycles in the middle to high latitudes of the northern hemisphere, which is attributed to the influence of stratospheric CH4 that varies at different latitudes. These findings provide insights into the global budget of atmospheric composition and the understanding of satellite measurement sensitivity to CH4.
BibTeX: @article{WOS:001018318900001, author = {Zhou, Lihang and Warner, Juying and Nalli, Nicholas R. and Wei, Zigang and Oh, Youmi and Bruhwiler, Lori and Liu, Xingpin and Divakarla, Murty and Pryor, Ken and Kalluri, Satya and Goldberg, Mitchell D.}, title = {Spatiotemporal Variability of Global Atmospheric Methane Observed from Two Decades of Satellite Hyperspectral Infrared Sounders}, journal = {REMOTE SENSING}, year = {2023}, volume = {15}, number = {12}, doi = {https://doi.org/10.3390/rs15122992} }
Song, H., Sheng, M., Lei, L., Guo, K., Zhang, S. and Ji, Z.	Spatial and Temporal Variations of Atmospheric CH4 in Monsoon Asia Detected by Satellite Observations of GOSAT and TROPOMI [Abstract] [BibTeX]	2023	REMOTE SENSING Vol. 15(13)	article	DOI
Abstract: Space-based measurements, such as the Greenhouse gases Observing SATellite (GOSAT) and the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite, provide global observations of the column-averaged CH4 concentration (XCH4). Due to the irregular observations and data gaps in the retrievals, studies on the spatial and temporal variations of regional atmospheric CH4 concentrations are limited. In this paper, we mapped XCH4 data over monsoon Asia using GOSAT and TROPOMI observations from April 2009 to December 2021 and analyzed the spatial and temporal pattern of atmospheric CH4 variations and emissions. The results show that atmospheric CH4 concentrations over monsoon Asia have long-term increases with an annual growth rate of roughly 8.4 ppb. The spatial and temporal trends of XCH4 data are significantly correlated with anthropogenic CH4 emissions from the bottom-up emission inventory of EDGAR. The spatial pattern of gridded XCH4 temporal variations in China presents a basically consistent distribution with the Heihe-Tengchong Line, which is mainly related to the difference in anthropogenic emissions in the eastern and western areas. Using the mapping of XCH4 data from 2019 to 2021, this study further revealed the response of atmospheric CH4 concentrations to anthropogenic emissions in different urban agglomerations. For the urban agglomerations, the triangle of Central China (TCC), the Chengdu-Chongqing City Group (CCG), and the Yangtze River Delta (YRD) show higher CH4 concentrations and emissions than the Beijing-Tianjin-Hebei region and nearby areas (BTH). The results reveal the spatial and temporal distribution of CH4 concentrations and quantify the differences between urban agglomerations, which will support further studies on the drivers of methane emissions.
BibTeX: @article{WOS:001031094300001, author = {Song, Hao and Sheng, Mengya and Lei, Liping and Guo, Kaiyuan and Zhang, Shaoqing and Ji, Zhanghui}, title = {Spatial and Temporal Variations of Atmospheric CH4 in Monsoon Asia Detected by Satellite Observations of GOSAT and TROPOMI}, journal = {REMOTE SENSING}, year = {2023}, volume = {15}, number = {13}, doi = {https://doi.org/10.3390/rs15133389} }
Mannisenaho, V., Tsuruta, A., Backman, L., Houweling, S., Segers, A., Krol, M., Saunois, M., Poulter, B., Zhang, Z., Lan, X., Dlugokencky, E.J., Michel, S., White, J.W.C. and Aalto, T.	Global Atmospheric delta(CH4)-C-13 and CH4 Trends for 2000-2020 from the Atmospheric Transport Model TM5 Using CH4 from Carbon Tracker Europe-CH4 Inversions [Abstract] [BibTeX]	2023	ATMOSPHERE Vol. 14(7)	article	DOI
Abstract: This study investigates atmospheric delta(CH4)-C-13 trends, as produced by a global atmospheric transport model using CH4 inversions from CarbonTracker-Europe CH4 for 2000-2020, and compares them to observations. The CH4 inversions include the grouping of the emissions both by delta(CH4)-C-13 isotopic signatures and process type to investigate the effect, and to estimate the CH4 magnitudes and model CH4 and delta(CH4)-C-13 trends. In addition to inversion results, simulations of the global atmospheric transport model were performed with modified emissions. The estimated global CH4 trends for oil and gas were found to increase more than coal compared to the priors from 2000-2006 to 2007-2020. Estimated trends for coal emissions at 30 degrees N-60 degrees N are less than 50% of those from priors. Estimated global CH4 rice emissions trends are opposite to priors, with the largest contribution from the EQ to 60 degrees N. The results of this study indicate that optimizing wetland emissions separately produces better agreement with the observed delta(CH4)-C-13 trend than optimizing all biogenic emissions simultaneously. This study recommends optimizing separately biogenic emissions with similar isotopic signature to wetland emissions. In addition, this study suggests that fossil-based emissions were overestimated by 9% after 2012 and biogenic emissions are underestimated by 8% in the inversion using EDGAR v6.0 as priors.
BibTeX: @article{WOS:001039147700001, author = {Mannisenaho, Vilma and Tsuruta, Aki and Backman, Leif and Houweling, Sander and Segers, Arjo and Krol, Maarten and Saunois, Marielle and Poulter, Benjamin and Zhang, Zhen and Lan, Xin and Dlugokencky, Edward J. and Michel, Sylvia and White, James W. C. and Aalto, Tuula}, title = {Global Atmospheric delta(CH4)-C-13 and CH4 Trends for 2000-2020 from the Atmospheric Transport Model TM5 Using CH4 from Carbon Tracker Europe-CH4 Inversions}, journal = {ATMOSPHERE}, year = {2023}, volume = {14}, number = {7}, doi = {https://doi.org/10.3390/atmos14071121} }

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