Improvements in the representation of the land carbon cycle in Earth system models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) include interactive treatment of both the carbon and nitrogen cycles, improved photosynthesis, and soil hydrology. To assess the impact of these model developments on aspects of the global carbon cycle, the Earth System Model Evaluation Tool is expanded to compare CO2 concentration and emission-driven historical simulations from CMIP5 and CMIP6 to observational data sets. Overestimations of photosynthesis (GPP) in CMIP5 were largely resolved in CMIP6 for participating models with an interactive nitrogen cycle, but remaining for models without one. This points to the importance of including nutrient limitation. Simulating the leaf area index (LAI) remains challenging with a large model spread in both CMIP5 and CMIP6. In ESMs, global mean land carbon uptake (NBP) is well reproduced in the CMIP5 and CMIP6 multi-model means. However, this is the result of an underestimation of NBP in the northern hemisphere, which is compensated by an overestimation in the southern hemisphere and the tropics. Overall, a slight improvement in the simulation of land carbon cycle parameters is found in CMIP6 compared to CMIP5, but with many biases remaining, further improvements of models in particular for LAI and NBP is required. Emission-driven simulations perform just as well as concentration driven models despite the added process-realism. Due to this we recommend ESMs in future CMIP phases to perform emission-driven simulations as the standard so that climate-carbon cycle feedbacks are fully active. The inclusion of nitrogen limitation led to a large improvement in photosynthesis compared to models not including this process, suggesting the need to view the nitrogen cycle as a necessary part of all future carbon cycle models.
UFLUX v2.0: A Process-Informed Machine Learning Framework for Efficient and Explainable Modelling of Terrestrial Carbon Uptake
University of Edinburgh（爱丁堡大学）；Royal Botanic Garden Edinburgh（爱丁堡皇家植物园）；University of Southampton（南安普顿大学）；National Space Science Center, Chinese Academy of Sciences（中国科学院国家空间科学中心）；Observatoire de Paris（巴黎天文台）；Sorbonne University（索邦大学）；University of Exeter（埃克塞特大学）；University of Amsterdam（阿姆斯特丹大学）
Modeling the response of the marine carbon cycle to extreme CO$_2$ injection events
Virginia Commonwealth University（弗吉尼亚联邦大学）；William and Mary（威廉与玛丽学院）；University of New Mexico（新墨西哥大学）；Thapar Institute of Engineering and Technology（塔帕尔工程技术学院）；The Open University（开放大学）；The Natural History Museum（自然历史博物馆）；University of Arizona（亚利桑那大学）
Quantitative implications of the secondary role of carbon dioxide climate forcing in the past glacial-interglacial cycles for the likely future climatic impacts of anthropogenic greenhouse-gas forcings
