HOW RESILIENT MAY THE AMAZON RAIN FOREST CARBON BALANCE BE TO CLIMATE CHANGE?
Description:
The Amazon region represents a large
stock of biomass as well as a potentially important sink for additional
atmospheric CO2. Climate change, land-use changes and their
interaction present a risk to this role in the global carbon cycle. Both
positive and negative feedbacks exist in the system that can lead to resilience
but also to accelerated break-down of the carbon stocks and sinks. A set of
linked projects will investigate elements of these processes in the coming
years.
Author's Names: Bart Kruijt, Flavio Luizao, Antonio Nobre, et al
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IMPACT OF THE SOUTHERN ANNULAR MODE ON THE SOUTHERN OCEAN CARBON CYCLE
Description:
The
Southern Annular Mode (SAM) is the
leading mode of intraseasonal to interannual variability over the entire
Southern Hemisphere, yet the impact of the SAM
on the Southern Ocean carbon cycle is largely unknown. We investigate the
impact of the SAM on surface wind,
sea surface temperature (SST), chlorophyll concentration, and sea ice
concentration on the basis of 8-day averaged satellite observations. We find that Southern Ocean circulation and
biogeochemistry react quite sensitively to this mode of variability,
potentially resulting in air-sea CO2 flux anomalies. Since variations
in atmospheric CO2 congruent with the SAM
are small, we hypothesize that the SAM
produces anomalous air-sea fluxes of both natural and anthropogenic CO2,
which act to compensate each other.
Author's Names: N.S. Lovenduski, N. Gruber, A. Hawes, and D.W.J. Thompson
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MECHANISMS IMPACTING INTER-ANNUAL VARIATIONS IN REGIONAL C18OO ISOFLUXES: MODEL ESTIMATES WITH ...
Description:
Temporal
and spatial distributions of the δ18O value of atmospheric CO2
(dCa) can be used to constrain regional
ecosystem carbon exchanges and linkages between carbon and water cycling.
However, our understanding of the substantial observed temporal and spatial
variability in dCa is limited. Among many contributing
factors, seasonal and inter-annual variations in climate are likely to be
important. In this study we investigate the impact of dry climatic conditions
on the ecosystem-atmosphere C18OO isoflux.
We conducted this study in the
U.S. Southern Great Plains using five-year monthly-averaged precipitation δ18O
values (δp) from the
National Atmospheric Deposition Program (NADP) network, Mesonet meteorological
forcing, and MODIS-derived NDVI and land-cover characterization. These data are
used to force the isotope ecosystem model ISOLSM [Riley et al., 2002; Riley et al., 2003] at 10 km resolution across the region for relatively
drier (2003) and wetter (2004) years. The model has been calibrated and tested
in the dominant herbaceous vegetation types in the region [Biraud et
al., this issue].
Author's Names: W.J. Riley, C.J. Still, R. Vachon, J. Welker, et al
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CLIMATE VARIABILITY IN THE PACIFIC NORTHWEST, USA AND THE IMPACT ON CARBON EXCHANGE IN AN ...
Description: Long-term micrometeorological measurements
(1998-2004) show high interannual variability in the atmosphere-ecosystem
exchange of carbon for a Pacific Northwest
coniferous old-growth forest. Earlier
work [Wharton et al. 2004] has shown that net ecosystem exchange of carbon (NEE)
in this forest is highly sensitive to any perturbations in climate, and in
particular, in precipitation and temperature anomalies. Here we present results
from the ACASA (Advanced Canopy Atmosphere-Soil Algorithm) model to investigate
NEE as it relates to various climate forcings, including a shift in precipitation
pattern and increase in air temperature.
Author's Names: S. Wharton, R.D. Pyles, M. Falk, E. González, and K.T. Paw U
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THE SOIL CARBON CO2 FERTILIZATION FACTOR: THE MEASURE OF AN ECOSYSTEM’S CAPACITY TO INCREASE ...
Description:
This research introduces the concept of a “CO2
fertilization factor for soil carbon” (SigmaCF). The SigmaCF is a measure of an
ecosystem’s capacity to increase soil carbon storage in response to elevated
carbon dioxide levels. This research describes the mathematical derivation of
SigmaCF and illustrates how SigmaCF can be determined experimentally, using
data from three different CO2 enrichment experiments. I have
developed this concept to compare the results of carbon dioxide enrichment
experiments having different soil carbon turnover times, different levels of CO2
enrichment, and different lengths of exposure to elevated carbon dioxide
levels. The SigmaCF can also be used to estimate increases in soil carbon
uptake due to observed contemporary increases in atmospheric carbon dioxide
levels. This approach approximates the extent to which elevated carbon dioxide
levels increase soil carbon storage. I calculated SigmaCF for three
experimental settings—a mixed forest, and stands of loblolly pine and white oak
trees—by measuring changes in carbon inventories and radiocarbon ratios. The
forest had a SigmaCF of 1.8, which would imply a global sequestration of 5.5
billion tons C/year during the 1990's (in the highly-unlikely event that all
terrestrial vegetation shows this same response to elevated carbon dioxide
levels). The loblolly pine stand had a SigmaCF of 0.9 (2.8 billion tons C/year)
and the white oak stand had a SigmaCF of 1.18 (3.5 billion tons C/year). These
results show that elevated carbon dioxide levels in the atmosphere are
increasing the flux of carbon from the atmosphere to soil.
Author's Names: K.G. Harrison
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EMISSIONS TARGETS FOR CO2 STABILIZATION AS MODIFIED BY CARBON CYCLE FEEDBACKS
Description:
This study examines
the potential for feedbacks between the carbon cycle, atmospheric carbon
dioxide (CO2) increases and climate change to affect the
anthropogenic emissions that are required to stabilize future levels of CO2
in the atmosphere. Using a coupled climate-carbon cycle model, I found that
positive carbon cycle-climate feedbacks reduced allowable emissions by an
amount that varied with the model’s climate sensitivity. Emissions were further reduced if CO2
fertilization was assumed to be inactive in the model, as this removed an
otherwise important negative feedback on atmospheric CO2.
Author's Names: H. Damon Matthews
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OBSERVED RESPONSE OF THE CO2 GROWTH RATE TO CLIMATE VARIATIONS
Description:
The world is moving in a direction of managing the carbon
cycle in order to limit the forcing of earth's climate by CO2 as
well as to limit acidification of the oceans.
We may expect limitations on emissions, sequestration of carbon and
enhancements of natural sinks. It would
be important to be able to observe and quantify the impact of any such measures
on the growth rate of CO2. Until now it has been difficult to
quantify changes of the growth rate of CO2 with confidence due to
the large year to year variations that are caused by climate variations. A statistical method has been developed to
predict the growth rate of CO2 based on observed variations of
climate parameters.
Author's Names: Pieter Tans
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Added on: 08-Aug-2005 Downloads: 24
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THE GLACIAL BURIAL HYPOTHESIS – MISSING LINK IN THE GLACIAL CO2 PROBLEM?
Description:
Organic carbon buried under the great ice sheets of
the Northern Hemisphere is suggested to be the missing link in the atmospheric
CO2 change over the glacial-interglacial cycles. At glaciation, the
advancement of continental ice sheets buries vegetation and soil carbon
accumulated during warmer periods. At deglaciation, this burial carbon is
released back into the atmosphere. In a simulation over two
glacial-interglacial cycles using a synchronously coupled atmosphere-land-ocean
carbon model forced by reconstructed climate change, I found a 547 Gt
terrestrial carbon release from glacial maximum to interglacial, resulting in a
60 Gt (about 30 ppmv) increase in the atmospheric CO2, with the
remainder absorbed by the ocean in a scenario in which ocean acts as a passive
buffer. This is in contrast to previous estimates of a land uptake at deglaciation.
This carbon source originates from glacial burial, continental shelf and other
land areas in response to changes in ice cover, sea level, and climate. The
input of light isotope enriched terrestrial carbon causes atmospheric Δ13C to drop by about 0.3permil at deglaciation,
followed by rapid rise towards a high interglacial value in response to oceanic
warming and regrowth on land. Together with other ocean based mechanisms such
as change in ocean temperature, the glacial burial hypothesis may offer a full
explanation of the observed 80-100 ppmv atmospheric CO2 change.
Author's Names: N. Zeng
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CLIMATE –CARBON CYCLE FEEDBACK ANALYSIS, RESULTS FROM THE C4MIP MODEL INTERCOMPARISON
Description:
Ten coupled climate-carbon cycle models were forced by
historical and SRES A2 anthropogenic emissions of CO2 for the
1850-2100 time period to study the coupling between climate change and the
carbon cycle. Each model ran two separate simulations in order to evaluate the climate-carbon
cycle feedback. All models agree that future climate change will reduce the
efficiency of the Earth system to absorb the anthropogenic CO2. A
larger fraction of CO2 will stay in the atmosphere if climate change
is accounted for. By the end of the 21st
century, this ranges between 20 ppm and 200 ppm depending on the model, the
majority of the models lying between 50 and 100 ppm. All models simulate a
negative sensitivity for both the land and the ocean carbon cycle to future
climate. However there is still a large uncertainty on the magnitude of these
sensitivities. Also, the majority of the models attribute most of the changes
to the land. Finally, most of the models locate the reduction of land carbon
uptake in the tropics. However, the attribution to changes in net primary
productivity versus changes in respiration is still subject to debate amongst
the models.
Author's Names: P. Friedlingstein, P. Cox, R. Betts, L. Bopp, et al
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THE INTERPLAY BETWEEN SOURCES OF METHANE AND BIOGENIC VOCS IN GLACIAL-INTERGLACIAL FLUCTUATIONS ...
Description: Recent analyses of ice core methane
concentrations have suggested that methane emissions from wetlands were the
primary driver for prehistoric changes in atmospheric methane. However, these
data conflict as to the location of wetlands, magnitude of emissions, and the
environmental controls on methane oxidation. The flux of other reactive trace
gases to the atmosphere also controls apparent atmospheric methane
concentrations because these compounds compete for the hydroxyl radical (OH),
which is the primary atmospheric sink for methane. In a series of coupled
biosphere-atmosphere chemistry-climate modelling experiments, we simulate the
methane and biogenic volatile organic compound emissions from the terrestrial
biosphere from the Last Glacial Maximum (LGM) to present. Using an atmospheric
chemistry-climate model, we simulate the atmospheric concentrations of methane,
the hydroxyl radical, and numerous other reactive trace gas species. Over the
past 21,000 years methane emissions from wetlands increased slightly to the end
of the Pleistocene, but then decreased again, reaching levels at the
preindustrial Holocene that were similar to the LGM.
Author's Names: Jed O. Kaplan, Gerd Folberth, and Didier A. Hauglustaine
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