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Five years of variability in the global carbon cycle: comparing an estimate from the Orbiting Carbon Observatory-2 and process-based models

2021; IOP Publishing; Volume: 16; Issue: 5 Linguagem: Inglês

10.1088/1748-9326/abfac1

1748-9326

Zichong Chen, D. N. Huntzinger, Junjie Liu, Shilong Piao, Xuhui Wang, Stephen Sitch, Pierre Friedlingstein, Peter Anthoni, Almut Arneth, Vladislav Bastrikov, Daniel S. Goll, Vanessa Haverd, Atul K. Jain, Émilie Joetzjer, Etsushi Kato, Sebastian Lienert, Danica Lombardozzi, Patrick McGuire, Joe R. Melton, Julia E. M. S. Nabel, Julia Pongratz, Benjamin Poulter, Hanqin Tian, A. Wiltshire, Sönke Zaehle, Scot M. Miller,

Atmospheric chemistry and aerosols

Abstract Year-to-year variability in CO 2 fluxes can yield insight into climate-carbon cycle relationships, a fundamental yet uncertain aspect of the terrestrial carbon cycle. In this study, we use global observations from NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite for years 2015–2019 and a geostatistical inverse model to evaluate 5 years of interannual variability (IAV) in CO 2 fluxes and its relationships with environmental drivers. OCO-2 launched in late 2014, and we specifically evaluate IAV during the time period when OCO-2 observations are available. We then compare inferences from OCO-2 with state-of-the-art process-based models (terrestrial biosphere model, TBMs). Results from OCO-2 suggest that the tropical grasslands biome (including grasslands, savanna, and agricultural lands within the tropics) makes contributions to global IAV during the 5 year study period that are comparable to tropical forests, a result that differs from a majority of TBMs. Furthermore, existing studies disagree on the environmental variables that drive IAV during this time period, and the analysis using OCO-2 suggests that both temperature and precipitation make comparable contributions. TBMs, by contrast, tend to estimate larger IAV during this time and usually estimate larger relative contributions from the extra-tropics. With that said, TBMs show little consensus on both the magnitude and the contributions of different regions to IAV. We further find that TBMs show a wide range of responses on the relationships of CO 2 fluxes with annual anomalies in temperature and precipitation, and these relationships across most of the TBMs have a larger magnitude than inferred from OCO-2. Overall, the findings of this study highlight large uncertainties in process-based estimates of IAV during recent years and provide an avenue for evaluating these processes against inferences from OCO-2.