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1. The global carbon budget 1959--2011

Author

Le Quéré, C., Andres, R. J., Boden, T., Conway, T., Houghton, R. A., House, J. I., Marland, G., Peters, G. P., van der Werf, G., Ahlström, A., Andrew, R. M., Bopp, L., Canadell, J. G., Ciais, P., Doney, S. C., Enright, C., Friedlingstein, P., Huntingford, C., Jain, A. K., Jourdain, C., Kato, E., Keeling, R. F., Klein Goldewijk, K., Levis, S., Levy, P., Lomas, M., Poulter, B., Raupach, M. R., Schwinger, J., Sitch, S., Stocker, B. D., Viovy, N., Zaehle, S., and Zeng, N.

Subjects
010504 meteorology & atmospheric sciences, 530 Physics, 13. Climate action, 11. Sustainability, 15. Life on land, 010501 environmental sciences, 7. Clean energy, 01 natural sciences, 0105 earth and related environmental sciences
Abstract

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties. We discuss changes compared to previous estimates, consistency within and among components, and methodology and data limitations. Based on energy statistics, we estimate that the global emissions of CO2 from fossil fuel combustion and cement production were 9.5 ± 0.5 PgC yr−1 in 2011, 3.0 percent above 2010 levels. We project these emissions will increase by 2.6% (1.9–3.5%) in 2012 based on projections of Gross World Product and recent changes in the carbon intensity of the economy. Global net CO2 emissions from Land-Use Change, including deforestation, are more difficult to update annually because of data availability, but combined evidence from land cover change data, fire activity in regions undergoing deforestation and models suggests those net emissions were 0.9 ± 0.5 PgC yr−1 in 2011. The global atmospheric CO2 concentration is measured directly and reached 391.38 ± 0.13 ppm at the end of year 2011, increasing 1.70 ± 0.09 ppm yr−1 or 3.6 ± 0.2 PgC yr−1 in 2011. Estimates from four ocean models suggest that the ocean CO2 sink was 2.6 ± 0.5 PgC yr−1 in 2011, implying a global residual terrestrial CO2 sink of 4.1 ± 0.9 PgC yr−1. All uncertainties are reported as ±1 sigma (68% confidence assuming Gaussian error distributions that the real value lies within the given interval), reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. This paper is intended to provide a baseline to keep track of annual carbon budgets in the future. All carbon data presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_V2012).

Published
2013
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2. REDD Mitigation

Author

Arcidiacono-Bársony, C., Ciais, P., Viovy, N., Vuichard, N., Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), ICOS-ATC (ICOS-ATC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation des Surfaces et Interfaces Continentales (MOSAIC), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Scanario, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Mitigation, REDD, 15. Life on land, 010501 environmental sciences, 01 natural sciences, Carbon Cycle, 13. Climate action, 11. Sustainability, General Earth and Planetary Sciences, Deforestation, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, General Environmental Science
Abstract

Tropical deforestation is a major driver of climate change accounting for ∼12% of global anthropogenic CO2 emissions. A mitigation strategy named Reduction Emission from Deforestation and forest Degradation (REDD) has been developed to tackle emissions due to forest loss in developing countries. REDD will be the core instrument in any post-2012 climate agreement according to the final document of the 15th UN Conference of the Parties. Nonetheless, REDD's implementation presents several political and scientific challenges. A review of current and future deforestation estimates in terms of forest surface change, carbon densities, and carbon fluxes is under preparation to aid the scientific community. REDD mitigation potential estimates and a case study have also been examined. Preliminary results of this review are presented.

Published
2011

3. The European carbon balance. Part 2: croplands

Author

Ciais, P., Wattenbach, M., Vuichard, N., Smith, P., Piao, S., Don, A., Luyssaert, S., Janssens, I. A., Bondeau, Alberte, Dechow, R., Leip, A., Smith, P. C., Beer, C., van Der Werf, G., Gervois, S., van Oost, K., Tomelleri, E., Freibauer, A., Schulze, E., Reichstein, M., Jung, M., Carvalhais, N., Rodenbeck, C., Arain, M., Baldocchi, D., Bonan, G., Cescatti, A., Lasslop, G., Lindroth, A., Lomas, M., Margolis, H., Oleson, K., Roupsard, O., Veenendaal, E., Viovy, N., Williams, C., Woodward, F., Papale, D., Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), ICOS-ATC (ICOS-ATC), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Free University of Berlin (FU), Modélisation des Surfaces et Interfaces Continentales (MOSAIC), Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University [Beijing], Laboratoire Bordelais de Recherche en Informatique (LaBRI), Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS), Institut méditerranéen de biodiversité et d'écologie marine et continentale (IMBE), Avignon Université (AU)-Aix Marseille Université (AMU)-Institut de recherche pour le développement [IRD] : UMR237-Centre National de la Recherche Scientifique (CNRS), European Commission, Department of Oceanography [Honolulu], University of Hawai‘i [Mānoa] (UHM), Department of Biogeochemical Integration [Jena], Max Planck Institute for Biogeochemistry (MPI-BGC), Max-Planck-Gesellschaft-Max-Planck-Gesellschaft, Faculty of Earth and Life Sciences [Amsterdam] (FALW), Vrije Universiteit Amsterdam [Amsterdam] (VU), Département de Géographie, Université Catholique de Louvain = Catholic University of Louvain (UCL), Max-Planck-Gesellschaft, Johann Heinrich von Thünen-Institut, Faculdade de Ciências e Tecnologia = School of Science & Technology (FCT NOVA), Universidade Nova de Lisboa = NOVA University Lisbon (NOVA), Max-Planck-Institut für Biogeochemie (MPI-BGC), Biometeorology lab [Berkeley], Department of Environmental Science, Policy, and Management [Berkeley] (ESPM), University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC)-University of California [Berkeley] (UC Berkeley), University of California (UC)-University of California (UC), JRC Institute for Environment and Sustainability (IES), European Commission - Joint Research Centre [Ispra] (JRC), Department of Physical Geography and Ecosystem Science [Lund], Lund University [Lund], Centre for Terrestrial Carbon Dynamics: National Centre for Earth Observation (CTCD), University of Sheffield [Sheffield], Fonctionnement et pilotage des écosystèmes de plantations (UPR Ecosystèmes de plantations), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad), Department of Forest Environment and Resources, Università degli studi della Tuscia [Viterbo], Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB), Centre National de la Recherche Scientifique (CNRS)-Institut de recherche pour le développement [IRD] : UMR237-Aix Marseille Université (AMU)-Avignon Université (AU), University of California [Berkeley], University of California-University of California-University of California [Berkeley], University of California-University of California, University of Tuscia, Carboeurope Synthesis Team, and Hydrology and Geo-environmental sciences

Subjects
010504 meteorology & atmospheric sciences, Biome, Climate change, Atmospheric sciences, 01 natural sciences, 7. Clean energy, Agricultural land, SDG 13 - Climate Action, Environmental Chemistry, SDG 2 - Zero Hunger, Biology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, General Environmental Science, 2. Zero hunger, Hydrology, Global and Planetary Change, Ecology, Primary production, 04 agricultural and veterinary sciences, Soil carbon, 15. Life on land, 13. Climate action, Greenhouse gas, [SDE]Environmental Sciences, 040103 agronomy & agriculture, 0401 agriculture, forestry, and fisheries, Environmental science, Terrestrial ecosystem, Arable land
Abstract

We estimated the long-term carbon balance [net biome production (NBP)] of European (EU-25) croplands and its component fluxes, over the last two decades. Net primary production (NPP) estimates, from different data sources ranged between 490 and 846 gC m−2 yr−1, and mostly reflect uncertainties in allocation, and in cropland area when using yield statistics. Inventories of soil C change over arable lands may be the most reliable source of information on NBP, but inventories lack full and harmonized coverage of EU-25. From a compilation of inventories we infer a mean loss of soil C amounting to 17 g m−2 yr−1. In addition, three process-based models, driven by historical climate and evolving agricultural technology, estimate a small sink of 15 g C m−2 yr−1 or a small source of 7.6 g C m−2 yr−1. Neither the soil C inventory data, nor the process model results support the previous European-scale NBP estimate by Janssens and colleagues of a large soil C loss of 90 ± 50 gC m−2 yr−1. Discrepancy between measured and modeled NBP is caused by erosion which is not inventoried, and the burning of harvest residues which is not modeled. When correcting the inventory NBP for the erosion flux, and the modeled NBP for agricultural fire losses, the discrepancy is reduced, and cropland NBP ranges between −8.3 ± 13 and −13 ± 33 g C m−2 yr−1 from the mean of the models and inventories, respectively. The mean nitrous oxide (N2O) flux estimates ranges between 32 and 37 g C Eq m−2 yr−1, which nearly doubles the CO2 losses. European croplands act as small CH4 sink of 3.3 g C Eq m−2 yr−1. Considering ecosystem CO2, N2O and CH4 fluxes provides for the net greenhouse gas balance a net source of 4247 g C Eq m−2 yr−1. Intensifying agriculture in Eastern Europe to the same level Western Europe amounts is expected to result in a near doubling of the N2O emissions in Eastern Europe. N2O emissions will then become the main source of concern for the impact of European agriculture on climate.

Published
2010

4. The European carbon balance: part 3: Forests

Author

Luyssaert, Sebastiaan, Ciais, Philippe, Piao, S.L., Schulze, Ernst-Detlef, Jung, Michaela, Zaehle, Sönke, Schelhaas, Mart-Jan, Reichstein, Markus, Churkina, Galina, Papale, Dario, Abril, Gwenaël, Beer, C., Grace, John, Loustau, Denis, Matteucci, Giorgio, Magnani, Federico, Nabuurs, Gert-Jan, Verbeeck, Hans, Sulkava, M., van Der Werf, Guido R., Janssens, I.A., Vetter, M., Paris, J.D., Bouriaud, O., Peylin, P., Viovy, N., Vuichard, N., Freibauer, A., Luyssaert S., Ciais P., Piao S., Schulze E.-D., Jung M., Zaehle S., Schelhaas M.J., Reichstein M., Churkina G., Papale D., Abril G., Beer C., Grace J., Loustau D., Matteucci G., Magnani F., Nabuurs G.J., Verbeeck H., Sulkava M., van der Werf G., Janssens I.A., Department of Biology, University of Antwerp (UA), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), ICOS-ATC (ICOS-ATC), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Max Planck Institute for Biogeochemistry (MPI-BGC), Max-Planck-Gesellschaft, Centre for Ecosystem Studies, ALTERRA, Università degli studi della Tuscia [Viterbo], Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Écologie fonctionnelle et physique de l'environnement (EPHYSE), Institut National de la Recherche Agronomique (INRA), ISAFom, National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Alma Mater Studiorum Università di Bologna [Bologna] (UNIBO), European Forest Institute = Institut Européen de la Forêt = Euroopan metsäinstituutti (EFI), Centre des Faibles Radioactivités, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Helsinki University of Technology, Partenaires INRAE, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam [Amsterdam] (VU), ICOS-RAMCES (ICOS-RAMCES), Modélisation des Surfaces et Interfaces Continentales (MOSAIC), Carboeurope Synthesis Team, Hydrology and Geo-environmental sciences, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Tuscia University, Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Consiglio Nazionale delle Ricerche [Roma] (CNR), VU University Amsterdam, and Vrije universiteit = Free university of Amsterdam [Amsterdam] (VU)

Subjects
GREENHOUSE GAS BALANCE, 010504 meteorology & atmospheric sciences, northern hardwood forest, EDDY COVARIANCE, reduces soil respiration, CE - Forest Ecosystems, 01 natural sciences, Wageningen Environmental Research, global database, ComputingMilieux_MISCELLANEOUS, General Environmental Science, media_common, SDG 15 - Life on Land, ECOSYSTEM MODELS, Global and Planetary Change, geography.geographical_feature_category, Ecology, Carbon sink, terrestrial ecosystems, 04 agricultural and veterinary sciences, wide reduction, Old-growth forest, Centre for Ecosystem Studies, climate-change, Terrestrial ecosystem, Temperate rainforest, old-growth forests, dissolved organic-carbon, [SDE.MCG]Environmental Sciences/Global Changes, Environmental Chemistry, media_common.cataloged_instance, European union, Biology, 0105 earth and related environmental sciences, geography, FOREST INVENTORIES, Soil organic matter, Primary production, Forestry, Soil carbon, 15. Life on land, Centrum Ecosystemen, 13. Climate action, EU-25, 040103 agronomy & agriculture, 0401 agriculture, forestry, and fisheries, Environmental science, nitrogen additions, temperate forests
Abstract

We present a new synthesis, based on a suite of complementary approaches, of the primary production and carbon sink in forests of the 25 member states of the European Union (EU-25) during 1990-2005. Upscaled terrestrial observations and model-based approaches agree within 25% on the mean net primary production (NPP) of forests, i.e. 520 +/- 75 g C m-2 yr-1 over a forest area of 1.32 x 106 km2 to 1.55 x 106 km2 (EU-25). New estimates of the mean long-term carbon forest sink (net biome production, NBP) of EU-25 forests amounts 75 +/- 20 g C m-2 yr-1. The ratio of NBP to NPP is 0.15 +/- 0.05. Estimates of the fate of the carbon inputs via NPP in wood harvests, forest fires, losses to lakes and rivers and heterotrophic respiration remain uncertain, which explains the considerable uncertainty of NBP. Inventory-based assessments and assumptions suggest that 29 +/- 15% of the NBP (i.e., 22 g C m-2 yr-1) is sequestered in the forest soil, but large uncertainty remains concerning the drivers and future of the soil organic carbon. The remaining 71 +/- 15% of the NBP (i.e., 53 g C m-2 yr-1) is realized as woody biomass increments. In the EU-25, the relatively large forest NBP is thought to be the result of a sustained difference between NPP, which increased during the past decades, and carbon losses primarily by harvest and heterotrophic respiration, which increased less over the same period.

Published
2010

5. Interactions between nitrogen deposition, land cover conversion, and climate change determine the contemporary carbon balance of Europe

Author

Heimann, M., Hughes, J., Zaehle, S., Heumann, B. W., Viovy, N., Ramankutty, N., Jones, C., Jung, M., Chen, Y., and Churkina, G.

Subjects
2. Zero hunger, 13. Climate action, 15. Life on land
Abstract

European ecosystems are thought to take up large amounts of carbon, but neither the rate nor the contributions of the underlying processes are well known. In the second half of the 20th century, carbon dioxide concentrations have risen by more that 100 ppm, atmospheric nitrogen deposition has more than doubled, and European mean temperatures were increasing by 0.02 circle C yr(-1). The extents of forest and grasslands have increased with the respective rates of 5800 km(2) yr(-1) and 1100 km(2) yr(-1) as agricultural land has been abandoned at a rate of 7000 km(2) yr(-1). In this study, we analyze the responses of European land ecosystems to the aforementioned environmental changes using results from four process-based ecosystem models: BIOME-BGC, JULES, ORCHIDEE, and O-CN. The models suggest that European ecosystems sequester carbon at a rate of 56 TgC yr(-1) (mean of four models for 1951-2000) with strong interannual variability (+/- 88 TgC yr(-1), average across models) and substantial inter-model uncertainty (+/- 39 TgC yr(-1)). Decadal budgets suggest that there has been a continuous increase in the mean net carbon storage of ecosystems from 85 TgC yr(-1) in 1980s to 108 TgC yr(-1) in 1990s, and to 114 TgC yr(-1) in 2000-2007. The physiological effect of rising CO

6. Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites

Author

Wu, D., Ciais, P., Viovy, N., Knapp, A. K., Wilcox, K., Bahn, M., Smith, M. D., Vicca, S., Fatichi, S., Zscheischler, J., He, Y., Li, X., Ito, A., Arneth, A., Harper, A., Ukkola, A., Paschalis, A., Poulter, B., Peng, C., Ricciuto, D., Reinthaler, D., Chen, G., Tian, H., Genet, H., Mao, J., Ingrisch, J., Nabel, J. E. S. M., Pongratz, J., Boysen, L. R., Kautz, M., Schmitt, M., Meir, P., Zhu, Q., Hasibeder, R., Sippel, S., Dangal, S. R. S., Sitch, S., Shi, X., Wang, Y., Luo, Y., Liu, Y., and Piao, S.

Subjects
13. Climate action, 15. Life on land
Abstract

Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry), whereas increases in ANPP are lower in magnitude in extreme wet years compared to reductions during extreme drought (negative asymmetry). Whether the current generation of ecosystem models with a coupled carbon–water system in grasslands are capable of simulating these asymmetric ANPP responses is an unresolved question. In this study, we evaluated the simulated responses of temperate grassland primary productivity to scenarios of altered precipitation with 14 ecosystem models at three sites: Shortgrass steppe (SGS), Konza Prairie (KNZ) and Stubai Valley meadow (STU), spanning a rainfall gradient from dry to moist. We found that (1) the spatial slopes derived from modeled primary productivity and precipitation across sites were steeper than the temporal slopes obtained from inter-annual variations, which was consistent with empirical data; (2) the asymmetry of the responses of modeled primary productivity under normal inter-annual precipitation variability differed among models, and the mean of the model ensemble suggested a negative asymmetry across the three sites, which was contrary to empirical evidence based on filed observations; (3) the mean sensitivity of modeled productivity to rainfall suggested greater negative response with reduced precipitation than positive response to an increased precipitation under extreme conditions at the three sites; and (4) gross primary productivity (GPP), net primary productivity (NPP), aboveground NPP (ANPP) and belowground NPP (BNPP) all showed concave-down nonlinear responses to altered precipitation in all the models, but with different curvatures and mean values. Our results indicated that most models overestimate the negative drought effects and/or underestimate the positive effects of increased precipitation on primary productivity under normal climate conditions, highlighting the need for improving eco-hydrological processes in those models in the future.

7. The terrestrial carbon budget of South and Southeast Asia

Author

Cervarich, M., Shu, S., Jain, A. K., Arneth, A., Canadell, J., Friedlingstein, P., Houghton, R. A., Kato, E., Koven, C., Patra, P., Poulter, B., Sitch, S., Stocker, B., Viovy, N., Wiltshire, A., and Zeng, N.

Subjects
13. Climate action, 15. Life on land, 7. Clean energy
Abstract

Accomplishing the objective of the current climate policies will require establishing carbon budget and flux estimates in each region and county of the globe by comparing and reconciling multiple estimates including the observations and the results of top-down atmospheric carbon dioxide (CO$_{2}$) inversions and bottom-up dynamic global vegetation models. With this in view, this study synthesizes the carbon source/sink due to net ecosystem productivity (NEP), land cover land use change (E$_{LUC}$), fires and fossil burning (E$_{FIRE}$) for the South Asia (SA), Southeast Asia (SEA) and South and Southeast Asia (SSEA = SA + SEA) and each country in these regions using the multiple top-down and bottom-up modeling results. The terrestrial net biome productivity (NBP = NEP – E$_{LUC}$ – E$_{FIRE}$) calculated based on bottom-up models in combination with E$_{FIRE}$ based on GFED4s data show net carbon sinks of 217 ± 147, 10 ± 55, and 227 ± 279 TgC yr$^{-1}$ for SA, SEA, and SSEA. The top-down models estimated NBP net carbon sinks were 20 ± 170, 4 ± 90 and 24 ± 180 TgC yr$^{-1}$. In comparison, regional emissions from the combustion of fossil fuels were 495, 275, and 770 TgC yr$^{-1}$, which are many times higher than the NBP sink estimates, suggesting that the contribution of the fossil fuel emissions to the carbon budget of SSEA results in a significant net carbon source during the 2000s. When considering both NBP and fossil fuel emissions for the individual countries within the regions, Bhutan and Laos were net carbon sinks and rest of the countries were net carbon source during the 2000s. The relative contributions of each of the fluxes (NBP, NEP, E$_{LUC}$, and E$_{FIRE}$, fossil fuel emissions) to a nation’s net carbon flux varied greatly from country to country, suggesting a heterogeneous dominant carbon fluxes on the country-level throughout SSEA.

8. Global Carbon Budget 2017

Author

Le Quéré, C., Andrew, R. M., Friedlingstein, P., Sitch, S., Pongratz, J., Manning, A. C., Ivar Korsbakken, J., Peters, G. P., Canadell, J. G., Jackson, R. B., Boden, T. A., Tans, P. P., Andrews, O. D., Arora, V. K., Bakker, D. C. E., Barbero, L., Becker, M., Betts, R. A., Bopp, L., Chevallier, F., Chini, L. P., Ciais, P., Cosca, C. E., Cross, J., Currie, K., Gasser, T., Harris, I., Hauck, J., Haverd, V., Houghton, R. A., Hunt, C. W., Hurtt, G., Ilyina, T., Jain, A. K., Kato, E., Kautz, M., Keeling, R. F., Klein Goldewijk, K., Körtzinger, A., Landschützer, P., Lefèvre, N., Lenton, A., Lienert, S., Lima, I., Lombardozzi, D., Metzl, N., Millero, F., Monteiro, P. M. S., Munro, D. R., Nabel, J. E. M. S., Nakaoka, S.-I., Nojiri, Y., Antonio Padin, X., Peregon, A., Pfeil, B., Pierrot, D., Poulter, B., Rehder, G., Reimer, J., Rödenbeck, C., Schwinger, J., Séférian, R., Skjelvan, I., Stocker, B. D., Tian, H., Tilbrook, B., Tubiello, F. N., Laan-Luijkx, I. T. V., Werf, G. R. V., Van Heuven, S., Viovy, N., Vuichard, N., Walker, A. P., Watson, A. J., Wiltshire, A. J., Zaehle, S., and Zhu, D.

Subjects
13. Climate action, 11. Sustainability, 15. Life on land, 7. Clean energy, 12. Responsible consumption

9. Recent trends and drivers of regional sources and sinks of carbon dioxide

Author

Sitch, S., Friedlingstein, P., Gruber, N., Jones, S.D., Murray-Tortarolo, G., Ahlström, A., Doney, S.C., Graven, H., Heinze, C., Huntingford, C., Levis, S., Levy, P.E., Lomas, M., Poulter, B., Viovy, N., Zaehle, S., Zeng, N., Arneth, A., Bonan, G., Bopp, L., Canadell, J.G., Chevallier, F., Ciais, P., Ellis, R., Loor, M., Peylin, P., Piao, S.L., Le Quere, C., Smith, B., Zhu, Z., and Myneni, R.

Subjects
13. Climate action, 15. Life on land

10. Impacts of extreme summers on European ecosystems: a comparative analysis of 2003, 2010 and 2018

Author

Bastos, A., Fu, Z., Ciais, P., Friedlingstein, P., Sitch, S., Pongratz, J., Weber, U., Reichstein, M., Anthoni, P., Arneth, A., Haverd, V., Jain, A., Joetzjer, E., Knauer, J., Lienert, Sebastian, Loughran, T., McGuire, P. C., Obermeier, W., Padrón, R. S., Shi, H., Tian, H., Viovy, N., and Zaehle, S.

Subjects
13. Climate action, 15. Life on land, 530 Physik
Abstract

In Europe, three widespread extreme summer drought and heat (DH) eventshave occurred in 2003, 2010 and 2018. These events were comparable inmagnitude but varied in their geographical distribution and biomes affected.In this study, we perform a comparative analysis of the impact of the DHevents on ecosystem CO2fluxes over Europe based on an ensemble of11 dynamic global vegetation models (DGVMs), and the observation-based FLUXCOM product. We find that all DH events were associatedwith decreases in net ecosystem productivity (NEP), but the gross summerflux anomalies differ between DGVMs and FLUXCOM. At the annualscale, FLUXCOM and DGVMs indicate close to neutral or above-averageland CO2uptake in DH2003 and DH2018, due to increased productivityin spring and reduced respiration in autumn and winter compensating forless photosynthetic uptake in summer. Most DGVMs estimate lower grossprimary production (GPP) sensitivity to soil moisture during extreme sum-mers than FLUXCOM. Finally, we show that the different impacts of the DHevents at continental-scale GPP are in part related to differences in veg-etation composition of the regions affected and to regional compensatingor offsetting effects from climate anomalies beyond the DH centres.This article is part of the theme issue‘Impacts of the 2018 severe droughtand heatwave in Europe: from site to continental scale’.

11. The Global Methane Budget 2000–2017

Author

Saunois, M., Stavert, A. R., Poulter, B., Bousquet, P., Canadell, J. G., Jackson, R. B., Raymond, P. A., Dlugokencky, E. J., Houweling, S., Patra, P. K., Ciais, P., Arora, V. K., Bastviken, D., Bergamaschi, P., Blake, D. R., Brailsford, G., Bruhwiler, L., Carlson, K. M., Carrol, M., Castaldi, S., Chandra, N., Crevoisier, C., Crill, P. M., Covey, K., Curry, C. L., Etiope, G., Frankenberg, C., Gedney, N., Hegglin, M. I., Höglund-Isaksson, L., Hugelius, G., Ishizawa, M., Ito, A., Janssens-Maenhout, G., Jensen, K. M., Joos, Fortunat, Kleinen, T., Krummel, P. B., Langenfelds, R. L., Laruelle, G. G., Liu, L., Machida, T., Maksyutov, S., McDonald, K. C., McNorton, J., Miller, P. A., Melton, J. R., Morino, I., Müller, Jurek, Murguia-Flores, F., Naik, V., Niwa, Y., Noce, S., O'Doherty, S., Parker, R. J., Peng, C., Peng, S., Peters, G. P., Prigent, C., Prinn, R., Ramonet, M., Regnier, P., Riley, W. J., Rosentreter, J. A., Segers, A., Simpson, I. J., Shi, H., Smith, S. J., Steele, L. P., Thornton, B. F., Tian, H., Tohjima, Y., Tubiello, F. N., Tsuruta, A., Viovy, N., Voulgarakis, A., Weber, T. S., van Weele, M., van der Werf, G. R., Weiss, R. F., Worthy, D., Wunch, D., Yin, Y., Yoshida, Y., Zhang, W., Zhang, Z., Zhao, Y., Zheng, B., Zhu, Q., and Zhuang, Q.

Subjects
13. Climate action, 530 Physics, 15. Life on land, 7. Clean energy
Abstract

Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is 29 Tg CH4 yr−1 larger than our estimate for the previous decade (2000–2009), and 24 Tg CH4 yr−1 larger than the one reported in the previous budget for 2003–2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr−1, range 594–881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (∼ 65 % of the global budget

12. Direct and seasonal legacy effects of the 2018 heat wave and drought on European ecosystem productivity

Author

Bastos, A., Ciais, P., Friedlingstein, P., Sitch, S., Pongratz, J., Fan, L., Wigneron, J. P., Weber, U., Reichstein, M., Fu, Z., Anthoni, P., Arneth, A., Haverd, V., Jain, A. K., Joetzjer, E., Knauer, J., Lienert, S., Loughran, T., McGuire, P. C., Tian, H., Viovy, N., and Zaehle, S.

Subjects
2. Zero hunger, 13. Climate action, fungi, food and beverages, 15. Life on land, 530 Physik
Abstract

n summer 2018, central and northern Europe were stricken by extreme drought and heat (DH2018). The DH2018 differed from previous events in being preceded by extreme spring warming and brightening, but moderate rainfall deficits, yet registering the fastest transition between wet winter conditions and extreme summer drought. Using 11 vegetation models, we show that spring conditions promoted increased vegetation growth, which, in turn, contributed to fast soil moisture depletion, amplifying the summer drought. We find regional asymmetries in summer ecosystem carbon fluxes: increased (reduced) sink in the northern (southern) areas affected by drought. These asymmetries can be explained by distinct legacy effects of spring growth and of water-use efficiency dynamics mediated by vegetation composition, rather than by distinct ecosystem responses to summer heat/drought. The asymmetries in carbon and water exchanges during spring and summer 2018 suggest that future land-management strategies could influence patterns of summer heat waves and droughts under long-term warming.

13. The Global Methane Budget: 2000–2017

Author

M. Saunois, A. R. Stavert, B. Poulter, P. Bousquet, J. G. Canadell, R. B. Jackson, P. A. Raymond, E. J. Dlugokencky, S. Houweling, P. K. Patra, P. Ciais, V. K. Arora, D. Bastviken, P. Bergamaschi, D. R. Blake, G. Brailsford, L. Bruhwiler, K. M. Carlson, M. Carrol, S. Castaldi, N. Chandra, C. Crevoisier, P. M. Crill, K. Covey, C. L. Curry, G. Etiope, C. Frankenberg, N. Gedney, M. I. Hegglin, L. Höglund-Isaksson, G. Hugelius, M. Ishizawa, A. Ito, G. Janssens-Maenhout, K. M. Jensen, F. Joos, T. Kleinen, P. B. Krummel, R. L. Langenfelds, G. G. Laruelle, L. Liu, T. Machida, S. Maksyutov, K. C. McDonald, J. McNorton, P. A. Miller, J. R. Melton, I. Morino, J. Müller, F. Murguia-Flores, V. Naik, Y. Niwa, S. Noce, S. O'Doherty, R. J. Parker, C. Peng, S. Peng, G. P. Peters, C. Prigent, R. Prinn, M. Ramonet, P. Regnier, W. J. Riley, J. A. Rosentreter, A. Segers, I. J. Simpson, H. Shi, S. J. Smith, L. P. Steele, B. F. Thornton, H. Tian, Y. Tohjima, F. N. Tubiello, A. Tsuruta, N. Viovy, A. Voulgarakis, T. S. Weber, M. van Weele, G. R. van der Werf, R. F. Weiss, D. Worthy, D. Wunch, Y. Yin, Y. Yoshida, W. Zhang, Z. Zhang, Y. Zhao, B. Zheng, Q. Zhu, Q. Zhuang, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Modélisation INVerse pour les mesures atmosphériques et SATellitaires (SATINV), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), CSIRO Marine and Atmospheric Research [Aspendale], Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), NASA Goddard Space Flight Center (GSFC), Department of Earth System Science [Stanford] (ESS), Stanford EARTH, Stanford University-Stanford University, Yale School of the Environment (YSE), NOAA/University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, SRON Netherlands Institute for Space Research (SRON), Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), ICOS-ATC (ICOS-ATC), Canadian Centre for Climate Modelling and Analysis (CCCma), Environment and Climate Change Canada, Department of Thematic Studies – Technology and Social Change, Linköping University (LIU), European Commission - Joint Research Centre [Ispra] (JRC), Department of Chemistry [Irvine], University of California [Irvine] (UC Irvine), University of California (UC)-University of California (UC), National Institute of Water and Atmospheric Research [Wellington] (NIWA), New York University [New York] (NYU), NYU System (NYU), Università degli studi della Campania 'Luigi Vanvitelli' = University of the Study of Campania Luigi Vanvitelli, Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Bolin Centre for Climate Research, Stockholm University, Skidmore College [Saratoga Springs], Pacific Climate Impacts Consortium, University of Victoria [Canada] (UVIC), Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Roma (INGV), Istituto Nazionale di Geofisica e Vulcanologia, Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Met Office Hadley Centre for Climate Change (MOHC), United Kingdom Met Office [Exeter], University of Reading (UOR), International Institute for Applied Systems Analysis [Laxenburg] (IIASA), National Institute for Environmental Studies (NIES), Oeschger Centre for Climate Change Research (OCCR), University of Bern, Max Planck Institute for Meteorology (MPI-M), Max-Planck-Gesellschaft, Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, VIC, Australia, Département de Physique [Bruxelles] (ULB), Faculté des Sciences [Bruxelles] (ULB), Université libre de Bruxelles (ULB)-Université libre de Bruxelles (ULB), Purdue Climate Change Research Center, Purdue University [West Lafayette], European Centre for Medium-Range Weather Forecasts (ECMWF), Lund University [Lund], Climate Research Division [Toronto], School of Geographical Sciences [Bristol], University of Bristol [Bristol], NOAA Geophysical Fluid Dynamics Laboratory (GFDL), National Oceanic and Atmospheric Administration (NOAA), Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), School of Chemistry [Bristol], NERC National Centre for Earth Observation (NCEO), Natural Environment Research Council (NERC), Université du Québec à Montréal = University of Québec in Montréal (UQAM), Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University [Beijing], Center for International Climate and Environmental Research [Oslo] (CICERO), University of Oslo (UiO), Observatoire de Paris, Université Paris sciences et lettres (PSL), Massachusetts Institute of Technology (MIT), ICOS-RAMCES (ICOS-RAMCES), Université libre de Bruxelles (ULB), Lawrence Berkeley National Laboratory [Berkeley] (LBNL), Centre for Coastal Biogeochemistry Research, Southern Cross University (SCU), TNO Climate, Air and Sustainability [Utrecht], The Netherlands Organisation for Applied Scientific Research (TNO), International Center for Climate and Global Change Research and School of Forestry and Wildlife Sciences, Auburn University, Joint Global Change Research Institute, Pacific Northwest National Laboratory (PNNL)-University of Maryland [College Park], University of Maryland System-University of Maryland System, CSIRO Oceans and Atmosphere, CISRO Oceans and Atmosphere, Department of Geological Sciences and Bolin Centre for Climate Research, FAO Forestry, Food and Agriculture Organization of the United Nations [Rome, Italie] (FAO), Finnish Meteorological Institute (FMI), Modélisation des Surfaces et Interfaces Continentales (MOSAIC), Department of Chemistry [Imperial College London], Imperial College London, University of Rochester [USA], Royal Netherlands Meteorological Institute (KNMI), Vrije Universiteit Amsterdam [Amsterdam] (VU), Scripps Institution of Oceanography (SIO - UC San Diego), University of California [San Diego] (UC San Diego), University of Toronto, Department of Physical Geography and Ecosystem Science [Lund], Department of Geographical Sciences [College Park], University of Maryland [College Park], Hohai University, European Project: 725546,Metlake, European Project: 776810,H2020,H2020-SC5-2017-OneStageB,VERIFY(2018), European Project: 773421,H2020,H2020-BG-2017-1,NUNATARYUK(2017), Natural Environment Research Council [2006-2012], Earth Sciences, Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Saunois, M., R. Stavert, A., Poulter, B., Bousquet, P., G. Canadell, J., B. Jackson, R., A. Raymond, P., J. Dlugokencky, E., Houweling, S., K. Patra, P., Ciais, P., K. Arora, V., Bastviken, D., Bergamaschi, P., R. Blake, D., Brailsford, G., Bruhwiler, L., M. Carlson, K., Carrol, M., Castaldi, S., Chandra, N., Crevoisier, C., M. Crill, P., Covey, K., L. Curry, C., Etiope, G., Frankenberg, C., Gedney, N., I. Hegglin, M., Hoglund-Isaksson, L., Hugelius, G., Ishizawa, M., Ito, A., Janssens-Maenhout, G., M. Jensen, K., Joos, F., Kleinen, T., B. Krummel, P., L. Langenfelds, R., G. Laruelle, G., Liu, L., Machida, T., Maksyutov, S., C. McDonald, K., Mcnorton, J., A. Miller, P., R. Melton, J., Morino, I., Muller, J., Murguia-Flores, F., Naik, V., Niwa, Y., Noce, S., O'Doherty, S., J. Parker, R., Peng, C., Peng, S., P. Peters, G., Prigent, C., Prinn, R., Ramonet, M., Regnier, P., J. Riley, W., A. Rosentreter, J., Segers, A., J. Simpson, I., Shi, H., J. Smith, S., Paul Steele, L., F. Thornton, B., Tian, H., Tohjima, Y., N. Tubiello, F., Tsuruta, A., Viovy, N., Voulgarakis, A., S. Weber, T., Van Weele, M., R. Van Der Werf, G., F. Weiss, R., Worthy, D., Wunch, D., Yin, Y., Yoshida, Y., Zhang, W., Zhang, Z., Zhao, Y., Zheng, B., Zhu, Q., and Zhuang, Q.

Subjects
Naturgeografi, 010504 meteorology & atmospheric sciences, TRACE GASES, ATMOSPHERIC METHANE, 010501 environmental sciences, Atmospheric sciences, 01 natural sciences, 7. Clean energy, Methane, chemistry.chemical_compound, CARBON-DIOXIDE, SDG 13 - Climate Action, Meteorology & Atmospheric Sciences, Climate change, CH4 EMISSIONS, Geosciences, Multidisciplinary, lcsh:Environmental sciences, ComputingMilieux_MISCELLANEOUS, lcsh:GE1-350, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 0303 health sciences, GREENHOUSE-GAS EMISSIONS, Atmospheric methane, lcsh:QE1-996.5, Géochimie, Geology, methane, global warming, climate change, greenhouse gases, Carbon project, Atmospheric chemistry, Physical Sciences, 0406 Physical Geography and Environmental Geoscience, BIOMASS BURNING EMISSIONS, NATURAL-GAS, PROCESS-BASED MODEL, 530 Physics, 03 medical and health sciences, SDG 17 - Partnerships for the Goals, Global Carbon Project, 0402 Geochemistry, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, 030304 developmental biology, 0105 earth and related environmental sciences, Science & Technology, Radiative forcing, 15. Life on land, Trace gas, lcsh:Geology, chemistry, TM 4D-VAR V1.0, Physical Geography, 13. Climate action, Greenhouse gas, GOSAT SWIR XCO2, General Earth and Planetary Sciences, Environmental science, Global methane (CH4) budget, 0401 Atmospheric Sciences
Abstract

Understanding and quantifying the global methane (CH4) budgetis important for assessing realistic pathways to mitigate climate change.Atmospheric emissions and concentrations of CH4 continue to increase,making CH4 the second most important human-influenced greenhouse gas interms of climate forcing, after carbon dioxide (CO2). The relativeimportance of CH4 compared to CO2 depends on its shorteratmospheric lifetime, stronger warming potential, and variations inatmospheric growth rate over the past decade, the causes of which are stilldebated. Two major challenges in reducing uncertainties in the atmosphericgrowth rate arise from the variety of geographically overlapping CH4sources and from the destruction of CH4 by short-lived hydroxylradicals (OH). To address these challenges, we have established aconsortium of multidisciplinary scientists under the umbrella of the GlobalCarbon Project to synthesize and stimulate new research aimed at improvingand regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paperdedicated to the decadal methane budget, integrating results of top-downstudies (atmospheric observations within an atmospheric inverse-modellingframework) and bottom-up estimates (including process-based models forestimating land surface emissions and atmospheric chemistry, inventories ofanthropogenic emissions, and data-driven extrapolations). For the 2008–2017 decade, global methane emissions are estimated byatmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximumestimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or∼ 60 % is attributed to anthropogenic sources, that isemissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is29 Tg CH4 yr−1 larger than our estimate for the previous decade (2000–2009),and 24 Tg CH4 yr−1 larger than the one reported in the previousbudget for 2003–2012 (Saunois et al. 2016). Since 2012, global CH4emissions have been tracking the warmest scenarios assessed by theIntergovernmental Panel on Climate Change. Bottom-up methods suggest almost30 % larger global emissions (737 Tg CH4 yr−1, range 594–881)than top-down inversion methods. Indeed, bottom-up estimates for naturalsources such as natural wetlands, other inland water systems, and geologicalsources are higher than top-down estimates. The atmospheric constraints onthe top-down budget suggest that at least some of these bottom-up emissionsare overestimated. The latitudinal distribution of atmosphericobservation-based emissions indicates a predominance of tropical emissions(∼ 65 % of the global budget, info:eu-repo/semantics/published

Published
2020

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