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

[ACG35-01] Contrasting historical and future warming in CESM2 versus CESM1

★Invited Papers

*Julie Arblaster¹, Gerald Meehl¹, Marika Holland¹ (1.Monash University, NCAR)

Climate variability and change is presented for the Community Earth System Model version 2 (CESM2), a state-of-the-art coupled climate model which includes various configurations, including a version with interactive chemistry and greater stratospheric resolution, CESM2(WACCM6) and the standard CESM2(CAM6). Many scientific improvements were implemented in the development of CESM2 from its predecessor CESM1, including key changes to the deep and shallow convection and boundary layer schemes and microphysics. Here we describe some simulated improvements in the CESM2 over its predecessor CESM1, including to the rainfall characteristics in the monsoon regions and their teleconnections to tropical variability. The CESM2 versions capture the time evolution of historical global temperatures and the contribution of various individual forcings to these changes is identified using detection and attribution experiments. The CESM2 models have higher equilibrium climate sensitivities compared to their corresponding high and low-top versions in CESM1, though interestingly their transient climate response is lower. Larger warming in the CESM2 by the end of the 21st Century under future emission scenarios is also found and associated with greater warming in the tropics compared to CESM1. Recent experiments with the CESM2 using the CMIP5 RCP8.5 scenario will be presented, helping to elucidate the role of changes in radiative forcing between CMIP5 and CMIP6 in driving these differences.