Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 17:00-18:30 UPMC Jussieu - ROOM 101 - Block 24/34

1116 - Biogeochemical feedbacks to climate change

Parallel Session

Lead Convener(s): C. Schaedel (Northern Arizona University, Flagstaff, AZ, United States of America)

Convener(s): C. Jones (Met Office Hadley Centre, Exeter, United Kingdom), P. Barré (CNRS, Paris, France)

17:00

Biogeochemical feedbacks to climate change: Insights into soil moisture controls on soil heterotrophic respiration

C. Chenu (Agroparistech, Grignon, France), F. Moyano (CNRS, Grignon, France), P. Garnier (INRA, Grignon, France), I. Virto (Universidad Pública de Navarra. Escuela Superior de Ingenieros Agrónomos, Pamplona, Spain)

Abstract details
Biogeochemical feedbacks to climate change: Insights into soil moisture controls on soil heterotrophic respiration

C. Chenu (1) ; F. Moyano (2) ; P. Garnier (3) ; I. Virto (4)
(1) Agroparistech, Umr ecosys, Grignon, France; (2) CNRS, Bioemco, Grignon, France; (3) INRA, Umr ecosys, Grignon, France; (4) Universidad Pública de Navarra. Escuela Superior de Ingenieros Agrónomos, Departamento de ciencias del medio natural, Pamplona, Spain

Abstract content

Soils contain the largest C terrestrial pool and even small changes in soil organic C (SOC) can have a significant impact on the atmospheric CO2 concentration. The C cycle feedback to climate will largely depend, in magnitude and timing, on the response of soil C to climate changes. However, there is still considerable uncertainty regarding such effects.

While the effect of temperature on soil C mineralization has been the subject of much work and considerable debate, much less attention has been paid to the effect of changes in water regime, another predicted component of climate change. However, soil moisture has a key role in regulating soil respiration. Here, we synthesise work regarding the relation between soil moisture and soil C dynamics, focusing on the underlying mechanisms, on the interaction with soil properties and other components of global changes, and discuss how mechanisms and the complexity of soils can be integrated into models.

The effect of soil moisture is complex to predict because, unlike that of temperature, it is strongly dependent on soil characteristics. Soil moisture effect on heterotrophic respiration is represented in most current carbon cycle models by empirical functions, which are often based on limited experimental data. We performed a data-driven analysis of soil moisture respiration relations and showed how these are consistently affected by soil properties such as clay content, organic C content, bulk density. We developed empirical models including the effects of soil texture, soil organic carbon and bulk density which improve the functions currently used in different soil biogeochemical models.

Partially responsible for the present state of knowledge may be the idea that, in biogeochemical models, time- and spatially averaged or approximate relationship of microbial activity with moisture is sufficient to reliably predict C fluxes. But soil microorganisms live in a complex 3-D framework of mineral and organic particles defining pores of various sizes, more or less inter-connected, which result in a variety of microhabitats. Most promising perspectives in this area are based on mechanistic approaches, where theoretical linkages between substrate and gas diffusivity in soil pores and heterotrophic respiration are explored in different soil matrices. A new generation of biogeochemical models is based on an explicit representation of soil architecture at a fine scale, which provides in-depth mechanistic understanding, and should help to define relevant descriptors of soil characteristics to improve how larger scale models account for the effects of soil moisture.  

The complex interplay between biological, biogeochemical and physical processes is apparent when considering the variability of soil C storage upon a widely used cropping practice: not tillage, where soil moisture also regulates the flows of C between soil litter and mineral layers.  The interactions between soil moisture and other components of global change, i.e. land use, cropping practices, temperature, will also result in biogeochemical feedbacks to climate change.

17:15

Observational constraints on biogeochemical feedbacks

C. Le Quéré (University of East Anglia, Norwich, United Kingdom)

Abstract details
Observational constraints on biogeochemical feedbacks

C. Le Quéré (1)
(1) University of East Anglia, Tyndall Centre for Climate Change Research, Norwich, United Kingdom

Abstract content

Tremendous efforts are underway to use a wider range of observations to inform model projections. Efforts range from enhanced coordination of repeat observations, the collection of quality controlled data in public databases, the development of new data interpolation methods, and extensive model-data comparison efforts. This presentation will provide an overview of efforts by the carbon cycle research community to constrain, using a range of observations, our quantitative understanding of how the carbon cycle works. It will use the trends and variability observed during 1959-2014 in a range of observations to examine how the land and ocean carbon sinks have responded to changes in increasing atmospheric CO2 and climate change and variability at the global and regional level, and comment on the qualities and limitations of models to project changes in the 21st century and beyond. This presentation will be based on the ‘Global Carbon Budget’ annual update by the Global Carbon Project. It includes an assessment of the annual change in land and ocean carbon sinks from three ocean data products, seven ocean models, eight dynamic global vegetation models, three atmospheric inversions, plus indirect constraints from CO2 emissions and measured atmospheric CO2 growth rate. The presentation will also include additional data and model analysis from the marine environment and discuss the marine biogeochemical feedbacks related to ocean deoxygenation and to the response of marine ecosystems to climate change and ocean acidification.

17:30

Projecting the carbon-climate feedback from thawing permafrost

C. Koven (Lawrence Berkeley National Laboratory, Berkeley, CA, United States of America), P. Ciais (LSCE, CEA, CNRS and UVSQ, Gif-sur-Yvette, France), P. Friedlingstein (University of Exeter, Exeter, United Kingdom), G. Grosse, (Alfred Wegener Institute, Potsdam, Germany), J. Harden (United States Geological Survey, Menlo Park, CA, United States of America), G. Hugelius, (Stockholm University, Stockholm, Sweden), D. M. Lawrence, (National Center for Atmospheric Research, Boulder, United States of America), D. Mcguire (United States Geological Survey, Fairbanks, AK, United States of America), W. J. Riley (Lawrence Berkeley National Laboratory, Berkeley, United States of America), C. Schaedel (Northern Arizona University, Flagstaff, United States of America), E. Schuur (Northern Arizona University, Flagstaff, AZ, United States of America)

Abstract details
Projecting the carbon-climate feedback from thawing permafrost

C. Koven (1) ; P. Ciais (2) ; J. Harden (3) ; G. Hugelius, (4) ; P. Friedlingstein (5) ; DM. Lawrence, (6) ; D. Mcguire (7) ; WJ. Riley (8) ; C. Schaedel (9) ; E. Schuur (10) ; G. Grosse, (11)
(1) Lawrence Berkeley National Laboratory, Berkeley, CA, United States of America; (2) LSCE, CEA, CNRS and UVSQ, Gif-sur-Yvette, France; (3) United States Geological Survey, Menlo Park, CA, United States of America; (4) Stockholm University, Department of physical geography and quaternary geology, bolin centre of climate research, Stockholm, Sweden; (5) University of Exeter, Exeter, United Kingdom; (6) National Center for Atmospheric Research, Boulder, United States of America; (7) United States Geological Survey, Fairbanks, AK, United States of America; (8) Lawrence Berkeley National Laboratory, Climate and carbon sciences, Berkeley, United States of America; (9) Northern Arizona University, Center for ecosystem science and society, Flagstaff, United States of America; (10) Northern Arizona University, Department of biological sciences, Flagstaff, AZ, United States of America; (11) Alfred Wegener Institute, Helmholtz centre for polar and marine research, periglacial research unit, Potsdam, Germany

Abstract content

The loss of carbon from ecosystems as they adjust to a warmer climate may act to amplify climate change.  Permafrost-affected ecosystems may be particularly vulnerable to such carbon losses because of the huge amounts of organic carbon that have been preserved in frozen soils, which may thaw and decompose more rapidly as a result of climate warming.  In the IPCC fifth assessment report, the models of the Earth system that were used to estimate the magnitude of these terresrial carbon-climate feedback processes did not include key representation of the CO2 and CH4 release from permafrost thaw. Recent progress has been made to synthesize observations of permafrost carbon dynamics and develop the representation of these processes in global carbon cycle models, to better estimate the amount and timing of greenhouse gas emissions from permafrost. I will discuss a variety of approaches to project the feedback from warming permafrost, from highly simplified and data-constrained soil models to detailed ecosystem models that include vegetation-permafrost-nutrient interactions. Such approaches suggest that the carbon-climate feedback from permafrost is an important process on the 50-300 year timescale, and that the magnitude of ecosystem carbon losses is highly sensitive to the future trajectory of fossil fuel emissions, with much larger losses under high emission scenarios such as RCP8.5 than on mitigated emissions pathways such as the RCP4.5 scenario.

17:45

Positive future climate feedback due to changes in oceanic DMS emissions

J. Tjiputra (Uni Research, Bergen, Norway), K. Six, (Max Planck Institute for Meteorology,, Hamburg, Germany), Ø. Seland (Norwegian Meteorological Institute, Oslo, Norway), C. Heinze (University of Bergen, Bergen, Norway)

Abstract details
Positive future climate feedback due to changes in oceanic DMS emissions

J. Tjiputra (1) ; K. Six, (2) ; Ø. Seland (3) ; C. Heinze (4)
(1) Uni Research, Uni climate, Bergen, Norway; (2) Max Planck Institute for Meteorology,, Hamburg, Germany; (3) Norwegian Meteorological Institute, Oslo, Norway; (4) University of Bergen, Geophysical institute, Bergen, Norway

Abstract content

The global ocean is the largest natural source of dimethylsulphide (DMS) gas to the atmosphere. DMS is produced by phytoplankton and is released to the surface ocean if cells are degraded. Once it enters the atmosphere, it might contribute to the nucleation particles important for cloud formation, which then effect the Earth’s radiation budget and climate. Future global warming and ocean acidification is projected to alter marine DMS production and emission. However the none of the models assessed in the last IPCC report includes the DMS-climate feedback.

Recent study indicated that under high CO2 emissions future, the oceanic DMS emission is projected to decrease by 12 to 24% by the end of this century, potentially leading to an equilibrium temperature response of 0.1K to 0.76K.

Here, for the first time using a fully interactive Earth system model including a microphysical aerosol module with sulfur chemistry, we perform simulations on future climate projection with coupled DMS feedback. Under the highest pH sensitivity, our simulation shows that projected DMS production and emission decrease relative to the preindustrial state by 50% and 36%, respectively toward the end of the 21st century under the RCP8.5 emissions scenario. The largest emission reduction is simulated in the Southern Ocean. On contrast, emissions at polar latitudes increase owing to the sea ice retreat. This large change in marine sulfur emisson leads to an additional global warming of 0.3K relative to the reference simulation without DMS-climate feedback at the end of the 21st century. Both simulations also produce similar trajectories in atmospheric CO2 concentration, consistent with little change in the cumulative oceanic and terrestrial carbon sinks.

18:00

How much carbon dioxide and methane will be released from thawing permafrost soils?

I. Hartley (University of Exeter, Exeter, United Kingdom), C. Estop Aragones (University of Exeter, Exeter, United Kingdom), M. Cooper (University of Exeter, Exeter, United Kingdom), J. Fisher (University of Sheffield, Sheffield, United Kingdom), C. Schaedel (Northern Arizona University, Flagstaff, AZ, United States of America), L. Street (Heriot Watt University, Edinburgh, United Kingdom), A. Thierry (University of Edinburgh, Edinburgh, United Kingdom), D. Charman (University of Exeter, Exeter, United Kingdom), M. Garnett (NERC Radiocarbon Facility, Glasgow, United Kingdom), E. Schuur (Northern Arizona University, Flagstaff, AZ, United States of America), J. Murton (University of Sussex, Chichester, United Kingdom), G. Phoenix (University of Sheffield, Sheffield, United Kingdom), P. Wookey (Heriot Watt University, Edinburgh, United Kingdom), M. Williams (University of Edinburgh, Edinburgh, United Kingdom)

Abstract details
How much carbon dioxide and methane will be released from thawing permafrost soils?

I. Hartley (1) ; C. Estop Aragones (1) ; M. Cooper (1) ; J. Fisher (2) ; C. Schaedel (3) ; L. Street (4) ; A. Thierry (5) ; D. Charman (1) ; M. Garnett (6) ; J. Murton (7) ; G. Phoenix (2) ; P. Wookey (4) ; M. Williams (5) ; E. Schuur (8)
(1) University of Exeter, Geography, College of Life and Environmental Sciences, Exeter, United Kingdom; (2) University of Sheffield, Animal and plant sciences, Sheffield, United Kingdom; (3) Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ, United States of America; (4) Heriot Watt University, School of life sciences, Edinburgh, United Kingdom; (5) University of Edinburgh, School of geosciences, Edinburgh, United Kingdom; (6) NERC Radiocarbon Facility, Glasgow, United Kingdom; (7) University of Sussex, Geography, Chichester, United Kingdom; (8) Northern Arizona University, Department of biological sciences, Flagstaff, AZ, United States of America

Abstract content

High northern latitudes are predicted to warm rapidly during the 21st century. The tundra, boreal forests and peatlands found in these regions are recognised to contain substantial stores of organic matter. Permafrost soils are particularly important in this context, storing as much carbon as all the rest of the world's soils put together, and more than twice as much carbon as the atmosphere. The IPCC AR5 report emphasises that there is high confidence that warming in the Arctic and Boreal will lead to a reduction in permafrost extent. However, while some estimates suggest that the potential for carbon release from thawing permafrost soil could be the single most important climate-carbon cycle feedback, the AR5 report also emphasises that there is low confidence in predicting rates of soil carbon loss, and also whether the carbon will be released mainly as carbon dioxide or the more powerful greenhouse gas, methane. Importantly, the permafrost feedback is not currently included in the models evaluated in the IPCC CMIP programme, and thus a potentially critical feedback is missing.

This presentation will focus on how recent studies, making detailed in situ observations, and running manipulative field and laboratory experiments, have improved understanding of the permafrost feedback. In particular, the presentation will: 1) explain the role of different high-latitude plant communities, including understudied groups such as mosses, in both controlling rates of thaw and potentially mitigating against some of the expected carbon release, 2) outline the important role radiocarbon dating has played in detecting the contribution of the decomposition of old, previously-frozen organic matter to rates of carbon release following permafrost thaw, and 3) discuss the potential for substantial amounts of permafrost carbon to be released in the form of methane.

Research has shown that in boreal forest, thick moss layers may insulate soils to such an extent that disturbances (e.g. fire) may be required before warming promotes deep permafrost thaw. Therefore, tundra and peatland ecosystems may thaw more rapidly due to wetter conditions or reduced thickness of insulating moss layers. Overall, it appears that there is indeed considerable potential for increased carbon dioxide production from thawing permafrost, especially from highly organic soils, and where soils are not permanently waterlogged post thaw. The latter issue requires a fuller consideration of water flow paths within permafrost landscapes. Given the potential for large soil carbon losses, it may be unlikely that these could be fully compensated for by increased plant growth, at least in tundra ecosystems where plant biomass is low. There does though remain the potential for increased soil carbon inputs from plants to reduce rates of soil carbon losses. On the other hand, rates of methane production from thawing permafrost may not be as high as first predicted. Rather, the direct effect of climate warming on rates of methanogenesis associated with the decomposition of contemporary carbon inputs in northern wetlands, is likely to be more important.

The permafrost feedback remains potentially one of the most important carbon cycle feedbacks to climate change, but requires considerable further study. Improving understanding of the proportion of previously-frozen organic matter that will decompose aerobically following thaw, and the extent to which nutrient release from thawing permafrost can increase plant growth and soil carbon inputs, should be considered as key ongoing research priorities.

18:15

Biomass burning in northern sub-Saharan Africa and associated changes in environmental and climate variables

C. Ichoku (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), L. Ellison, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), C. Gatebe, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), R. Poudyal, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), T. Matsui, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), E. Willmot, (Vanderbilt University, Nashville, TN, United States of America), T. Gabbert, (South Dakota School of Mines & Technology (SDSMT), Rapid City, SD, United States of America), J. Wang, (University of Nebraska, Lincoln, NE, United States of America), Y. Yue, (University of Nebraska, Lincoln, NE, United States of America), R. Damoah, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), J. Lee, (University of Missouri, Kansas City, MO, United States of America), J. Adegoke, (University of Missouri, Kansas City, MO, United States of America), J. Bolten, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), F. Policelli, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), E. Wilcox, (Desert Research Institute (DRI), Reno, NV, United States of America), F. Hosseinpour, (Desert Research Institute (DRI), Reno, NV, United States of America), S. Habib, (NASA Goddard Space Flight Center, Greenbelt, MD, United States of America), C. Okonkwo, (Howard University, Washington, DC, United States of America), F. Engelbrecht, (Centre for Scientific and Industrial Research, Pretoria, South Africa)

Abstract details
Biomass burning in northern sub-Saharan Africa and associated changes in environmental and climate variables

C. Ichoku (1) ; L. Ellison, (2) ; C. Gatebe, (3) ; R. Poudyal, (2) ; T. Matsui, (4) ; E. Willmot, (5) ; T. Gabbert, (6) ; J. Wang, (7) ; Y. Yue, (7) ; R. Damoah, (3) ; J. Lee, (8) ; J. Adegoke, (8) ; J. Bolten, (1) ; F. Policelli, (1) ; E. Wilcox, (9) ; F. Hosseinpour, (9) ; S. Habib, (1) ; C. Okonkwo, (10) ; F. Engelbrecht, (11)
(1) NASA Goddard Space Flight Center, Earth sciences division, code 610, Greenbelt, MD, United States of America; (2) NASA Goddard Space Flight Center, Science systems & applications, inc. (ssai), Greenbelt, MD, United States of America; (3) NASA Goddard Space Flight Center, Universities space research association (usra), Greenbelt, MD, United States of America; (4) NASA Goddard Space Flight Center, Earth system science interdisciplinary center (essic), Greenbelt, MD, United States of America; (5) Vanderbilt University, Nashville, TN, United States of America; (6) South Dakota School of Mines & Technology (SDSMT), Rapid City, SD, United States of America; (7) University of Nebraska, Lincoln, NE, United States of America; (8) University of Missouri, Kansas City, MO, United States of America; (9) Desert Research Institute (DRI), Reno, NV, United States of America; (10) Howard University, Washington, DC, United States of America; (11) Centre for Scientific and Industrial Research, Natural resources and the environment, Pretoria, South Africa

Abstract content

One of the most vulnerable tropical regions of the world is the northern sub-Saharan African (NSSA) region, which is bounded on the north and south by the Sahara and the Equator, respectively, and stretching East-West across Africa. This is so because of the highly active environmental and meteorological processes associated with its unique location and human activities. Over the years, this region has suffered frequent severe droughts that have caused tremendous hardship and loss of life to millions of its inhabitants due to the rapid depletion of the regional water resources. On the other hand, the NSSA region shows one of the highest biomass-burning rates per unit land area among all regions of the world. Because of the high concentration and frequency of fires in this region, with the associated abundance of heat release and gaseous and particulate smoke emissions, biomass-burning activity is believed to be one of the drivers of the regional carbon and energy cycles, with serious implications for the water cycle and climate. This extensive biomass-burning phenomenon contributes to environmental change, whose effects on the regional climate variability can be significant, with far-reaching implications for societal adaptation. An interdisciplinary research effort sponsored by the United States National Aeronautics and Space Administration (NASA) is presently being focused on the NSSA region, to better understand possible connections between the intense biomass burning observed from satellite year after year across the region and the water cycle, through associated changes in certain essential climate variables (ECVs) including land-cover, albedo, soil moisture, evapotranspiration, and atmospheric composition, which can drive changes in additional ECVs such as atmospheric water vapor and wind patterns, precipitation, surface runoff, and groundwater recharge. A combination of remote sensing and modeling approaches is being utilized to investigate these multiple processes to establish possible links between them. We are finding appreciable relationships between biomass burning and many of the above-listed ECVs. In this presentation, we will discuss interesting results as well as the path toward improved understanding of the interrelationships and feedbacks between the water cycle components and the environmental change dynamics due to biomass burning and related processes in the NSSA region.