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Atmospheric carbon dioxide (CO2) concentration is increasing rapidly since the Industrial Revolution, which has led to unequivocal global warming and crucial environmental change. It is extremely important to investigate interactions among atmospheric CO2, physical climate system and carbon cycle in underlying surface for a better understanding the Earth system. Earth system models are widely used to investigate these interactions by a coupled carbon-climate simulation. The Chinese Academy of Sciences Earth System Model version 2 (CAS-ESM2) has successfully fixed a two-way coupling of atmospheric CO2 with climate and carbon cycle in land and ocean. Using CAS-ESM2, we conducted a coupled carbon-climate simulation by following the CMIP6 proposal of historical emission-driven experiment. This study examines the modeled CO2 by a comparison to observed CO2 in sites Mauna Loa and Barrow, the Greenhouse Gases Observing Satellite (GOSAT) CO2 product. The compared results show that CAS-ESM2 agrees very well with observations in reproducing the increasing trend of annual CO2 during the period 18502014 and in capturing the seasonal cycle of CO2 in the two baseline sites, as well as over northern high latitudes. These agreements illustrate a good ability of CAS-ESM2 in simulating carbon-climate interactions, even though uncertainties remain in the processes. This study reports an important stage of the development of CAS-ESM with the carbon and climate coupled, and this coupling will provide significant scientific supports for climate research and Chinas goal of carbon neutrality.
Zhu et al. (Fri,) studied this question.