[A-CG35] 地球規模環境変化の予測と検出

[ACG35-P05] Millennium time-scale experiments with doubled CO2 concentration by Earth system models

*羽島 知洋¹、山本 彬友¹、河宮 未知生¹、蘇 宣銘¹、渡辺 路生¹、大垣内 るみ¹、建部 洋晶¹ (1.独立行政法人 海洋研究開発機構)

キーワード：地球システムモデル、炭素循環、気候変動

Earth system models (ESMs) are commonly used for simulating the climate–carbon (C) cycle, being applied to century-long climate simulations. Although millennium-long simulations have not been the main target of the models' simulations because of the computational cost, such long-term simulations can provide basic fundamental properties of climate-C cycle models and can be a help to understand the long-term behavior of climate, carbon dioxide (CO2) concentration, and carbon cycle. This study used two ESMs (MIROC-ESM and MIROC-ES2L) to investigate millennium-scale climate and C cycle adjustment to external forcing. The CO2 concentration was doubled abruptly at the beginning of the model simulations and kept at that level for the next 1000 or 2000 years. The simulation results were compared with transient simulations of 1% CO2 increase (1pctCO2). Unlike the 1pctCO2 experiment, the change in temperature–cumulative anthropogenic C emission relationship (so called TCRE) was non-linear over the millennium time-scales. The differences in TCRE among existing models suggest large uncertainty in the changes in temperature and cumulative emission in the millennium-long climate-C simulations. Ocean C and heat transport were found to be disconnected over millennium time-scales, leading to a longer time-scale of ocean C accumulation than heat uptake. Although the experimental design used here was highly idealized, this long-lasting C uptake by the ocean should be considered as part of the stabilization of CO2 concentration and global warming.