The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Fortunat Joos - One of the best experts on this subject based on the ideXlab platform.
-
ensemble reconstruction constraints on the Global Carbon Cycle sensitivity to climate
Nature, 2010Co-Authors: David Frank, Fortunat Joos, Jan Esper, Christoph C Raible, Ulf Buntgen, Valerie M Trouet, Benjamin D StockerAbstract:The processes controlling the Carbon flux and Carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive and are likely to provide a positive feedback leading to amplified anthropogenic warming. Owing to this feedback, at timescales ranging from interannual to the 20-100-kyr Cycles of Earth's orbital variations, warming of the climate system causes a net release of CO(2) into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the Global Carbon Cycle (termed gamma), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in Global warming projections. Here we quantify the median gamma as 7.7 p.p.m.v. CO(2) per degrees C warming, with a likely range of 1.7-21.4 p.p.m.v. CO(2) per degrees C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO(2) data from three ice cores, provide robust constraints for gamma on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of gamma is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of gamma calculated from any of ten coupled Carbon-climate models, we find that gamma is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of approximately 40 p.p.m.v. CO(2) per degrees C (refs 6, 7), and correspondingly suggest approximately 80% less potential amplification of ongoing Global warming.
-
ensemble reconstruction constraints on the Global Carbon Cycle sensitivity to climate
Nature, 2010Co-Authors: David Frank, Fortunat Joos, Jan Esper, Christoph C Raible, Ulf Buntgen, Valerie M Trouet, Benjamin D StockerAbstract:Climate warming tends to cause a net release of CO2, which in turn causes an amplification of warming. Estimates of the magnitude of this effect vary widely, leading to a wide range in Global warming projections. Recent work suggested that the magnitude of this positive feedback might be about 40 parts per million by volume of CO2 per °C of warming. David Frank and colleagues use three Antarctic ice cores and a suite of climate reconstructions to show that the feedback is likely to be much smaller, with a median of only about 8 p.p.m.v. CO2 per °C. Anthropogenic Global warming is likely to be amplified by positive feedback from the Global Carbon Cycle; however, the magnitude of the climate sensitivity of the Global Carbon Cycle, and thus of its positive feedback strength, is under debate. By combining a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO2 data from three ice cores, this climate sensitivity is now shown to be much smaller than previously thought. The processes controlling the Carbon flux and Carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive1,2,3,4 and are likely to provide a positive feedback leading to amplified anthropogenic warming3. Owing to this feedback, at timescales ranging from interannual to the 20–100-kyr Cycles of Earth's orbital variations1,5,6,7, warming of the climate system causes a net release of CO2 into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the Global Carbon Cycle (termed γ), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in Global warming projections8,9. Here we quantify the median γ as 7.7 p.p.m.v. CO2 per °C warming, with a likely range of 1.7–21.4 p.p.m.v. CO2 per °C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO2 data from three ice cores, provide robust constraints for γ on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of γ is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of γ calculated from any of ten coupled Carbon–climate models, we find that γ is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of ∼40 p.p.m.v. CO2 per °C (refs 6, 7), and correspondingly suggest ∼80% less potential amplification of ongoing Global warming.
-
holocene Carbon Cycle dynamics based on co2 trapped in ice at taylor dome antarctica
Nature, 1999Co-Authors: Andreas Indermuhle, Martin Wahlen, Bruce Deck, J Tschumi, Dominick Mastroianni, Thomas F Stocker, Fortunat Joos, H J Smith, H Fischer, Thomas BlunierAbstract:A high-resolution ice-core record of atmospheric CO2 concentration over the Holocene epoch shows that the Global Carbon Cycle has not been in steady state during the past 11,000 years. Analysis of the CO2 concentration and Carbon stable-isotope records, using a one-dimensional Carbon-Cycle model,uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial-scale changes of atmospheric CO2 concentrations.
Dhongil Lim - One of the best experts on this subject based on the ideXlab platform.
-
Enhanced terrigenous organic matter input and productivity on the western margin of the Western Pacific Warm Pool during the Quaternary sea-level lowstands: Forcing mechanisms and implications for the Global Carbon Cycle
Quaternary Science Reviews, 2020Co-Authors: Shiming Wan, Christophe Colin, Peter D. Clift, Fengming Chang, Rongtao Sun, Dhongil LimAbstract:Abstract Changes in terrigenous organic matter (OM) input, productivity and the associated bottom-water redox conditions, together with forcing mechanisms and Global Carbon Cycle implications of such variations, on the western margin of the Western Pacific Warm Pool (WPWP) during the Quaternary remain controversial. In this study, we reconstructed the hydrological dynamics, terrigenous OM input, productivity, and deep-sea redox conditions using one core from the continental slope of the Philippine Sea. The new data were integrated with published proxies from the same core and two additional cores from the abyssal Philippine Sea. The results exhibited noticeable variations in the abovementioned indicators, in correspondence to changes in the supply of terrigenous material. The continental slope deposition featured signals of strong physical erosion and chemical weathering of unconsolidated sediments on the exposed continental shelf during the Quaternary sea-level lowstands, which significantly contributed to increased terrigenous OM input and productivity and, in turn, decreased bottom-water oxygenation and atmospheric CO2 concentrations. In the abyssal Philippine Sea, increased Asian dust-driven OM input and productivity also acted as a sink of atmospheric CO2 during sea-level lowstands. Analysis of the data suggested that the enhanced terrigenous OM input and biological pump and thus the decreased dissolved oxygen level of the bottom water on the western margin of the WPWP played important roles in modifying the Global Carbon Cycle during sea-level lowstands. In contrast, the influence of hydrological dynamics on terrigenous OM input, productivity, and redox conditions therein during the Quaternary was limited.
David Frank - One of the best experts on this subject based on the ideXlab platform.
-
contribution of semi arid ecosystems to interannual variability of the Global Carbon Cycle
Nature, 2014Co-Authors: David Frank, Benjamin Poulter, Philippe Ciais, Ranga B Myneni, Niels Andela, Jian Bi, Gregoire Broquet, J G Canadell, Frederic ChevallierAbstract:The unusually large land Carbon sink reported in 2011 can mostly be attributed to semi-arid vegetation growth in the Southern Hemisphere following increased rainfall and long-term greening trends. Land and ocean take up around half of the annual anthropogenic Carbon emissions, and a thorough understanding of this process is important for predicting future greenhouse gas concentrations and thus climate change. This study investigates the largest uptake of land Carbon since atmospheric CO2 measurements began in 1958. Three independent methods of Global Carbon budget determination point to an exceptionally large land Carbon sink in response to extraordinary La Nina rainfall in semi-arid regions in the Southern Hemisphere, with almost 60% of Carbon uptake attributed to the Australian ecosystem and an increase in the sensitivity of continental net Carbon uptake to precipitation. Tropical rainforests have been thought to dominate the terrestrial processes driving Global Carbon Cycle interannual variability, but this work suggests that semi-arid biomes might become the dominant drivers in future. The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric Carbon dioxide concentrations1. Although the uptake of Carbon by oceanic and terrestrial processes has kept pace with accelerating Carbon dioxide emissions until now, atmospheric Carbon dioxide concentrations exhibit a large variability on interannual timescales2, considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests3. We use a terrestrial biogeochemical model, atmospheric Carbon dioxide inversion and Global Carbon budget accounting methods to investigate the evolution of the terrestrial Carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land Carbon sink reported in 2011 (ref. 2). Here we show that our three terrestrial Carbon sink estimates are in good agreement and support the finding of a 2011 record land Carbon sink. Surprisingly, we find that the Global Carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of Carbon uptake attributed to Australian ecosystems, where prevalent La Nina conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net Carbon uptake to precipitation. Our findings suggest that the higher turnover rates of Carbon pools in semi-arid biomes are an increasingly important driver of Global Carbon Cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the Carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.
-
contribution of semi arid ecosystems to interannual variability of the Global Carbon Cycle
Nature, 2014Co-Authors: Benjamin Poulter, David Frank, Philippe Ciais, Ranga B Myneni, Niels Andela, Gregoire Broquet, J G Canadell, Frederic Chevallier, Yi Y Liu, Steven W RunningAbstract:The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric Carbon dioxide concentrations. Although the uptake of Carbon by oceanic and terrestrial processes has kept pace with accelerating Carbon dioxide emissions until now, atmospheric Carbon dioxide concentrations exhibit a large variability on interannual timescales, considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests. We use a terrestrial biogeochemical model, atmospheric Carbon dioxide inversion and Global Carbon budget accounting methods to investigate the evolution of the terrestrial Carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land Carbon sink reported in 2011 (ref. 2). Here we show that our three terrestrial Carbon sink estimates are in good agreement and support the finding of a 2011 record land Carbon sink. Surprisingly, we find that the Global Carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of Carbon uptake attributed to Australian ecosystems, where prevalent La Nina conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net Carbon uptake to precipitation. Our findings suggest that the higher turnover rates of Carbon pools in semi-arid biomes are an increasingly important driver of Global Carbon Cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the Carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.
-
ensemble reconstruction constraints on the Global Carbon Cycle sensitivity to climate
Nature, 2010Co-Authors: David Frank, Fortunat Joos, Jan Esper, Christoph C Raible, Ulf Buntgen, Valerie M Trouet, Benjamin D StockerAbstract:Climate warming tends to cause a net release of CO2, which in turn causes an amplification of warming. Estimates of the magnitude of this effect vary widely, leading to a wide range in Global warming projections. Recent work suggested that the magnitude of this positive feedback might be about 40 parts per million by volume of CO2 per °C of warming. David Frank and colleagues use three Antarctic ice cores and a suite of climate reconstructions to show that the feedback is likely to be much smaller, with a median of only about 8 p.p.m.v. CO2 per °C. Anthropogenic Global warming is likely to be amplified by positive feedback from the Global Carbon Cycle; however, the magnitude of the climate sensitivity of the Global Carbon Cycle, and thus of its positive feedback strength, is under debate. By combining a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO2 data from three ice cores, this climate sensitivity is now shown to be much smaller than previously thought. The processes controlling the Carbon flux and Carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive1,2,3,4 and are likely to provide a positive feedback leading to amplified anthropogenic warming3. Owing to this feedback, at timescales ranging from interannual to the 20–100-kyr Cycles of Earth's orbital variations1,5,6,7, warming of the climate system causes a net release of CO2 into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the Global Carbon Cycle (termed γ), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in Global warming projections8,9. Here we quantify the median γ as 7.7 p.p.m.v. CO2 per °C warming, with a likely range of 1.7–21.4 p.p.m.v. CO2 per °C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO2 data from three ice cores, provide robust constraints for γ on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of γ is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of γ calculated from any of ten coupled Carbon–climate models, we find that γ is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of ∼40 p.p.m.v. CO2 per °C (refs 6, 7), and correspondingly suggest ∼80% less potential amplification of ongoing Global warming.
-
ensemble reconstruction constraints on the Global Carbon Cycle sensitivity to climate
Nature, 2010Co-Authors: David Frank, Fortunat Joos, Jan Esper, Christoph C Raible, Ulf Buntgen, Valerie M Trouet, Benjamin D StockerAbstract:The processes controlling the Carbon flux and Carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive and are likely to provide a positive feedback leading to amplified anthropogenic warming. Owing to this feedback, at timescales ranging from interannual to the 20-100-kyr Cycles of Earth's orbital variations, warming of the climate system causes a net release of CO(2) into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the Global Carbon Cycle (termed gamma), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in Global warming projections. Here we quantify the median gamma as 7.7 p.p.m.v. CO(2) per degrees C warming, with a likely range of 1.7-21.4 p.p.m.v. CO(2) per degrees C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO(2) data from three ice cores, provide robust constraints for gamma on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of gamma is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of gamma calculated from any of ten coupled Carbon-climate models, we find that gamma is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of approximately 40 p.p.m.v. CO(2) per degrees C (refs 6, 7), and correspondingly suggest approximately 80% less potential amplification of ongoing Global warming.
Vincent Chaplot - One of the best experts on this subject based on the ideXlab platform.
-
soil Carbon losses by sheet erosion a potentially critical contribution to the Global Carbon Cycle
Earth Surface Processes and Landforms, 2015Co-Authors: Daniel Mullernedebock, Vincent ChaplotAbstract:Despite soil erosion through water being a ubiquitous process and its environmental consequences being well understood, its effects upon the Global Carbon Cycle still remain largely uncertain. How much soil organic Carbon (SOC) is removed each year from soils by sheet wash, an important if not the most efficient mechanism of detachment and transport of surficial soil material? What are the main environnemental controls worldwide? These are important questions which largely remain unanswered. Empirical data from 240 runoff plots studied over entire rainy seasons from different regions of the world were analysed to estimate particulate organic Carbon (POC) losses (POCL), and POC enrichment in the sediments compared to the bulk soil (ER), which can be used as a proxy of the fate of the eroded POC. The median POCL was 9.9 g C m-2 y-1 with highest values observed for semi-arid soils (POCL = 10.8 g C m-2 y-1), followed by tropical soils (POCL = 6.4 g C m-2 y-1) and temperate soils (POCL = 1.7 g C m-2 y-1). Considering the mean POCL of 27.2 g C m-2 y-1, the total amount of SOC displaced annually by sheet erosion from its source would be 1.32 ± 0.20 Gt C, i.e. 14.6% of the net annual fossil fuel induced C emissions of 9 Gt C. Because of low sediment enrichment in POC, erosion-induced CO2 emissions are likely to be limited in clayey environments while POC burial within hillslopes is likely to constitute an important Carbon sink. In contrast, most of the POC displaced from sandy soils is likely to be emitted to the atmosphere. These results underpin the major role sheet wash plays in the displacement of SOC from its source and in the fate of the eroded SOC, with large variations across the different pedo-climatic regions of the world. Copyright © 2015 John Wiley & Sons, Ltd.
Shiming Wan - One of the best experts on this subject based on the ideXlab platform.
-
Enhanced terrigenous organic matter input and productivity on the western margin of the Western Pacific Warm Pool during the Quaternary sea-level lowstands: Forcing mechanisms and implications for the Global Carbon Cycle
Quaternary Science Reviews, 2020Co-Authors: Shiming Wan, Christophe Colin, Peter D. Clift, Fengming Chang, Rongtao Sun, Dhongil LimAbstract:Abstract Changes in terrigenous organic matter (OM) input, productivity and the associated bottom-water redox conditions, together with forcing mechanisms and Global Carbon Cycle implications of such variations, on the western margin of the Western Pacific Warm Pool (WPWP) during the Quaternary remain controversial. In this study, we reconstructed the hydrological dynamics, terrigenous OM input, productivity, and deep-sea redox conditions using one core from the continental slope of the Philippine Sea. The new data were integrated with published proxies from the same core and two additional cores from the abyssal Philippine Sea. The results exhibited noticeable variations in the abovementioned indicators, in correspondence to changes in the supply of terrigenous material. The continental slope deposition featured signals of strong physical erosion and chemical weathering of unconsolidated sediments on the exposed continental shelf during the Quaternary sea-level lowstands, which significantly contributed to increased terrigenous OM input and productivity and, in turn, decreased bottom-water oxygenation and atmospheric CO2 concentrations. In the abyssal Philippine Sea, increased Asian dust-driven OM input and productivity also acted as a sink of atmospheric CO2 during sea-level lowstands. Analysis of the data suggested that the enhanced terrigenous OM input and biological pump and thus the decreased dissolved oxygen level of the bottom water on the western margin of the WPWP played important roles in modifying the Global Carbon Cycle during sea-level lowstands. In contrast, the influence of hydrological dynamics on terrigenous OM input, productivity, and redox conditions therein during the Quaternary was limited.
