Characteristics of Future Warmer Base States in CESM2
The response of the earth system in a future warmer climate can produce insights into the functioning of the climate system as well as provide guidance regarding magnitudes of feedbacks that produce future changes to Earth’s climate. New model versions must be documented with regards to changes from previous versions and in comparison to other new model versions such as E3SMv1 and other CMIP6 models.
New model versions of CESM2(CAM6) (standard configuration) and CESM2(WACCM6) (high-top version) are compared to the previous CESM1 as well as to the current E3SMv1 for future warmer climate simulations and single forcing simulations. New higher values of equilibrium climate sensitivity (ECS) in CESM2 and E3SM have implications for the model responses to those changes in external forcings.
The CESM2(CAM6) and CESM2(WACCM6) have equilibrium climate sensitivity (ECS), 5.3°C, and 4.8°C respectively, at the high end of the range of the current CMIP6 models, similar to E3SMv1 (5.3°C). However, they have about the same transient climate response (TCR), 2.1°C, and 2.0°C respectively, compared to CESM1. Future global warming diverges around 2050, with greater warming by end of the century in the higher forcing scenarios and in both versions of CESM2 compared to CESM1. There is more future warming (and greater precipitation increase) in the tropics in the CESM2 versions compared to CESM1.