We present results from the NASA GISS ModelE2.1‐G‐CC Earth System Model with coupled climate‐carbon cycle simulations that were submitted to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) Coupled Climate‐Carbon Cycle MIP (C4MIP). Atmospheric CO₂ concentration and carbon budgets for the land and ocean in the historical simulations were generally consistent with observations. Low simulated atmospheric CO₂ concentrations during 1850–1950 were due to excess uptake from prescribed land cover change, which erroneously replaced arid shrublands with higher biomass crops, and assumed high 2004 LAI values in vegetated lands throughout the historical simulation. At the end of the historical period, slightly higher simulated CO₂ than observed resulted from the land being an insufficient net carbon sink, despite the net effect of CO₂ fertilization and warming‐induced increases to leaf photosynthetic capacity. The global ocean carbon uptake agreed well with the observations with the largest discrepancies in the low latitudes. Future climate projection at 2091–2100 agreed with CMIP5 models in the northward shift, of temperate deciduous forest climate and expansion across Eurasia along 60°N latitude, and dramatic regional biome shifts from drying and warming in continental Europe. Carbon feedback parameters were largely similar to the CMIP5 model ensemble. For our model, the variation of land feedback parameters within the uncertainty arises from the fertilization feedback being less sensitive due to lack of increased vegetation growth, and the comparably more negative ocean carbon‐climate feedback is due to the large slowdown of the Atlantic overturning circulation.

中文翻译：

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NASA GISS ModelE2.1中的全球碳循环和气候反馈

我们介绍了NASA GISS ModelE2.1‐G‐CC地球系统模型的结果以及气候-碳循环耦合模拟结果，该模拟结果已提交给耦合模型比对计划（CMIP6）的气候-碳循环耦合MIP（C4MIP）的第六阶段。历史模拟中陆地和海洋的大气CO ₂浓度和碳收支总体上与观测结果一致。在1850年至1950年期间，模拟大气CO ₂浓度较低是由于规定的土地覆被变化引起的过量吸收，这错误地将干旱灌木丛替换为生物量较高的农作物，并且在整个历史模拟过程中都假定植被土地的LAI值较高。在历史期末，模拟的CO ₂略高尽管有CO ₂的净影响，但由于土地净碳汇不足，导致比预期的多施肥和增温导致叶片光合能力增强。全球海洋碳吸收量与低纬度地区最大差异的观测结果非常吻合。2091–2100年的未来气候预测与北移的CMIP5模型，温带落叶林气候和沿60°N纬度的整个欧亚大陆的扩张以及欧洲大陆从干燥和变暖的剧烈区域生物群落转移相一致。碳反馈参数在很大程度上类似于CMIP5模型集合。对于我们的模型，土地反馈参数在不确定性范围内的变化是由于施肥反馈由于缺乏植被增长而敏感性降低，而相对较负的海洋碳-气候反馈则是由于大西洋翻转环流的减缓。