Siberian and temperate ecosystems shape Northern Hemisphere atmospheric CO2 seasonal amplification

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Lin, Xin, Rogers, Brendan M., Sweeney, Colm O., Chevallier, Frédéric, Arshinov, Mikhail Yu, Dlugokencky, Edward J., Machida, Toshinobu, Sasakawa, Motoki, Tans, Pieter P., Keppel-Aleks, Gretchen
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), 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)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Modélisation INVerse pour les mesures atmosphériques et SATellitaires (SATINV), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-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)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), National Aeronautics and Space Administration, NASA: NNX17AE13G, NNX17AC61A, ACKNOWLEDGMENTS. This study was funded by a NASA Carbon Cycle Science and Arctic-Boreal Vulnerability Experiment (ABoVE) grant (NNX17AE13G) to X.L., G.K.-A., and B.M.R., as well as a NASA ABoVE grant (NNX17AC61A) to C.S. M.S. acknowledges financial support by the Global Environmental Research Coordination System from Ministry of the Environment of Japan. We thank data providers of two CO2 inversion products: CAMS version 17r1 from European Centre for Medium-Range Weather Forecast and CarbonTracker CT2017 provided by NOAA’s Global Monitoring Laboratory, Boulder, CO. We are grateful to the GEOS-Chem model development group and the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) development group. We also thank L. Birch for valuable discussions. This research was supported in part through computational resources and services provided by Advanced Research Computing at the University of Michigan, Ann Arbor.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: Amplification; Arctic-boreal; Carbon dioxide; Global change; Seasonal cycle; [SDV]Life Sciences [q-bio]; Arctic; Browning; Siberia
• Online Access: https://hal.science/hal-03032371; https://hal.science/hal-03032371/document; https://hal.science/hal-03032371/file/21079.full.pdf; https://doi.org/10.1073/pnas.1914135117

International audience The amplitude of the atmospheric CO2 seasonal cycle has increased by 30 to 50% in the Northern Hemisphere (NH) since the 1960s, suggesting widespread ecological changes in the northern extratropics. However, substantial uncertainty remains in the continental and regional drivers of this prominent amplitude increase. Here we present a quantitative regional attribution of CO2 seasonal amplification over the past 4 decades, using a tagged atmospheric transport model prescribed with observationally constrained fluxes. We find that seasonal flux changes in Siberian and temperate ecosystems together shape the observed amplitude increases in the NH. At the surface of northern high latitudes, enhanced seasonal carbon exchange in Siberia is the dominant contributor (followed by temperate ecosystems). Arctic-boreal North America shows much smaller changes in flux seasonality and has only localized impacts. These continental contrasts, based on an atmospheric approach, corroborate heterogeneous vegetation greening and browning trends from field and remote-sensing observations, providing independent evidence for regionally divergent ecological responses and carbon dynamics to global change drivers. Over surface midlatitudes and throughout the midtroposphere, increased seasonal carbon exchange in temperate ecosystems is the dominant contributor to CO2 amplification, albeit with considerable contributions from Siberia. Representing the mechanisms that control the high-latitude asymmetry in flux amplification found in this study should be an important goal for mechanistic land surface models moving forward.