[A-CG35] Projection and detection of global environmental change

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

*Tomohiro Hajima¹, Akitomo Yamamoto¹, Michio Kawamiya¹, Xuaming Su¹, Michio Watanabe¹, Rumi Ohgaito¹, Hiroaki Tatebe¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Earth system model, Carbon cycle, Climate change

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.