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Category: Main/Abstracts/Carbon Cycle Response to Environmental Change


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  THE CHANGING CARBON CYCLE  Popular
Description:

The carbon cycle has undergone changes from 1998-2003 as a result of extensive droughts.  The CO2 seasonal amplitude at MLO halted its increase, and the CO2 growth rate accelerated as a result of a slowing down of the North American carbon sink.  In a series of coupled carbon-climate model experiments, we show a greater probability of drier soils in the 21st century, especially in the tropics and in mid-latitude summers as temperature-driven evapotranspiration exceed precipitation, and a positive feedback between the carbon cycle and climate. This positive feedback reduces the land and ocean’s capacity to store fossil fuel CO­ and accelerates the warming. A fossil fuel emission accelerating rapidly as the sink capacities decrease leads to further increases in the airborne fraction of fossil fuel CO2.


Author's Names: I. Fung
Filesize: 58.93 Kb
Added on: 28-Jul-2005 Downloads: 160
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  THE EFFECTS OF NITROGEN ADDITION ON THE BELOWGROUND CARBON CYCLE IN TEMPERATE FORESTS AND DESERT 
Description:
Human activities such as fossil fuel and fertilizer-use have doubled the amount of biologically active nitrogen entering ecosystems each year [Vitousek et al., 1997].  N is the limiting nutrient in many ecosystems and N availability has been shown to affect plant, root, and soil respiration.  For several temperate forests, experimental addition of N is associated with a decline in soil CO2 efflux [Bowden et al., 2004; Burton et al., 2004; Nohrstedt et al., 1989; Swanston et al., 2004].  This decline could be due to either (1) decreased allocation of C to root metabolism and growth because N demand of plants can be met with less energy expended belowground, or (2) decomposition rate due to changes in leaf or root tissue chemistry, or to changes in the decomposer community.  In contrast, the few studies of more water limited systems do not show decreased soil respiration fluxes [Schaeffer et al., 2003; Verburg et al., 2004], which could reflect hydrologic control of belowground C allocation.

Author's Names: N.S. Nowinski, S.E. Trumbore, E.B. Allen, et al
Filesize: 18.62 Kb
Added on: 03-Aug-2005 Downloads: 20
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  THE EXPRESSION OF BIOSPHERE RESPONSE TO LIGHT LEVEL CHANGES ON 18O OF ATMOSPHERIC CO2  Popular
Description:

Observations suggest the global reflectivity of Earth changed during recent decades. Although there is some ambiguity surrounding these findings, it is clear that, should there be changes in clouds or scattering aerosols, a change in the total solar radiation received at the surface and the fraction of diffuse light could result. Intriguingly, the d18O of CO2 time series measured at Mauna Loa shows variability during the 1990s that does not match secular trends in CO2 concentration or d13C. While a decrease in total solar radiation alone would reduce biospheric productivity, an increase in diffuse light can increase productivity, as has been argued for the period following the eruption of Pinatubo. Moreover, since the changes in radiation affect the surface latent energy exchange, the isotopic composition of terrestrial water with which CO2 interacts (specifically leaf and soil water) will be modified and can thus drive a change in isotopic fluxes.


Author's Names: N. Buenning, D. Noone, C. Still, W. Riley, et al
Filesize: 227.29 Kb
Added on: 27-Jul-2005 Downloads: 144
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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
Filesize: 58.69 Kb
Added on: 09-Aug-2005 Downloads: 23
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  THE INFLUENCE OF THE NAO ON THE CONTINENTAL SHELF PUMP ON THE NORTHWEST-EUROPEAN SHELF 
Description:

Using a coupled 3D hydrodynamic-biogeochemical model system for the Northwest-European shelf we simulated the years 1993-96, which exhibit an extremely strong transition from a NAOI-high to a NAOI-low regime. The induced temperature-shift had two consequences for the carbon budget of the North Sea: Firstly it increased the CO2 solubility and secondly it destabilized the water column in spring 1996. The latter effect was the precondition for mixing events which brought new nitrogen for primary production into the upper layer. Consequently the air-sea flux was 540 Gmol C a-1 in 1996, the NAOI-low year, and it was 203 Gmol C a-1 in 1995, the year with the highest NAOI.


Author's Names: J. Paetsch, W. Kuehn, A.V. Borges, Y. Bozec, et al
Filesize: 16.39 Kb
Added on: 03-Aug-2005 Downloads: 20
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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
Filesize: 106.89 Kb
Added on: 29-Jul-2005 Downloads: 24
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  THE MID-LATITUDE WESTERLIES, ATMOSPHERIC CO2 AND CLIMATE CHANGE DURING THE ICE AGES 
Description:

An idealized general circulation model is constructed of the ocean’s deep circulation and CO2 system that reproduces the main features of glacial-interglacial CO2 cycles, including the tight correlation between atmospheric CO2 and Antarctic temperatures, the lead of Antarctic temperatures over CO2 at terminations, and the shift of the ocean’s 13C minimum from the North Pacific to the Atlantic sector of the Southern Ocean. The model is based on a new idea about the nature of the glacial-interglacial cycles in which the driving force is independent of the orbital forcing and is not in the ocean. The key to glacial-interglacial transitions, we claim, is a relationship between the mid-latitude westerly winds, atmospheric CO2, and the mean state of the atmosphere. Cold glacial climates seem to have equatorward-shifted westerlies, which allow more respired CO2 to accumulate in the deep ocean. Warm climates like the present have poleward-shifted westerlies that flush respired CO2 out of the deep ocean.


Author's Names: J.R. Toggweiler, J.L. Russell, S.R. Carson
Filesize: 12.05 Kb
Added on: 04-Aug-2005 Downloads: 19
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  THE POTENTIAL FOR WIDESPREAD, THRESHOLD DIEBACK OF FORESTS IN NORTH AMERICA UNDER RAPID GLOBAL ... 
Description:

The MC1 Dynamic General Vegetation Model (DGVM) was used to assess the impacts of global warming on North American ecosystems, north of Mexico, under 6 future climate scenarios (3 General Circulation Models X 2 emission scenarios).  The simulations were begun in 1900 using observed climate and CO2 until 2000, then transferring to the future scenarios to 2100.  Carbon sequestration over the continent occurred in the late 20th century and for a short period into the 21st century, being fostered largely by increased precipitation, enhanced water-use efficiency and mild temperature increases.  However, these ‘greening’ processes were overtaken by the exponential effects of increasing temperature on evaporative demand and respiration, producing a subsequent decline. Simulation experiments suggested that fire suppression could significantly mitigate the carbon losses, yet many ecosystems were still forced to a lower carrying capacity.


Author's Names: R.P. Neilson, J.M. Lenihan, D. Bachelet, et al
Filesize: 39.41 Kb
Added on: 03-Aug-2005 Downloads: 26
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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
Filesize: 11.91 Kb
Added on: 29-Jul-2005 Downloads: 22
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  THE WINTER ARCTIC OSCILLATION, THE TIMING OF SPRING, AND CARBON FLUXES IN THE NORTHERN HEMISPHERE 
Description:

Increased winter temperatures associated with the observed positive trend in the winter Arctic Oscillation can partially explain trends towards earlier spring leafout in the northern hemisphere.  Increased spring drawdown associated with earlier leafout, coupled with increased winter respiration due to warmer temperatures, indicate the trend in the winter Arctic Oscillation can help explain observed increases in the seasonal amplitude of atmospheric CO2 concentration.


Author's Names: K.M. Schaefer, A.S. Denning, and O. Leonard
Filesize: 68.55 Kb
Added on: 04-Aug-2005 Downloads: 27
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     Talk History
Friday, September 30
· Discussion Panel
· Nitrogen Regulation of Carbon Sequestration in Terrestrial Ecosystems in Respons
· The Role of Water Relations in Driving Grassland Ecosystem Responses to Rising A
· Unraveling the Decline in High-latitude Surface Ocean Carbonate
Thursday, September 29
· Hazards of Temperature on Food Availability in Changing Environments (HOT-FACE)
· The Amazon and the Modern Carbon Cycle
· New Coupled Climate-carbon Simulations from the IPSL Model
· The Changing Carbon Cycle
· What are the Most Important Factors for Climate-carbon Cycle Coupling?
· CO2 Uptake of the Marine Biosphere
· European-wide Reduction in Primary Productivity Caused by the Heat and Drought i
· Persistence of Nitrogen Limitation over Terrestrial Carbon Uptake
· Atmospheric CO2, Carbon Isotopes, the Sun, and Climate Change over the Last Mill
· Proposing a Mechanistic Understanding of Atmospheric CO2 During the late Pleist
· Greenhouse Gas (CO2, CH4) and Climate Evolution since 650 kyrs Deduced from Anta
Wednesday, September 28
· (In and) Out of Africa: Estimating the Carbon Exchange of a Continent
· Recent Shifts in Soil Dynamics on Growing Season Length, Productivity, and...
· Interannual Variability in the Carbon Exchange Using an Ecosystem-fire Model
· Photosynthesis and Respiration in Forests in Response to Environmental Changes
· Seasonal and Interannual Variability in Net Ecosystem CO2 Exchange in Japan
· Estimating Landscape-level Carbon Fluxes from Tower CO2 Mixing Ratio Measurement
· Monitoring Effects in Climate and Fire Regime on Net Ecosystem Production
· Radiative Forcing from a Boreal Forest Fire
· The Influence of Soil and Water Management on Carbon Erosion and Burial
· Spatial and Temporal Patterns of CO2, CH4, and N2O Fluxes in Ecosystems
· Modeling the History of Terrestrial Carbon Sources and Sinks
· The Age of Carbon Respired from Terrestrial Ecosystems
· Discussion Panel
· The Underpinnings of Land Use History
Tuesday, September 27
· Regional CO2 Fluxes for North America Estimated from NOAA/CMDL Observatories

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The 7th International CO2 Conference

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September 25th - 30th
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