Processes controlling Southern Ocean shortwave climate feedbacks in CESM

Abstract

A climate model (Community Earth System Model with the Community Atmosphere Model version 5 (CESM‐CAM5)) is used to identify processes controlling Southern Ocean (30–70°S) absorbed shortwave radiation (ASR). In response to 21st century Representative Concentration Pathway 8.5 forcing, both sea ice loss (2.6 W m −2 ) and cloud changes (1.2 W m −2 ) enhance ASR, but their relative importance depends on location and season. Poleward of ~55°S, surface albedo reductions and increased cloud liquid water content (LWC) have competing effects on ASR changes. Equatorward of ~55°S, decreased LWC enhances ASR. The 21st century cloud LWC changes result from warming and near‐surface stability changes but appear unrelated to a small (1°) poleward shift in the eddy‐driven jet. In fact, the 21st century ASR changes are 5 times greater than ASR changes resulting from large (5°) naturally occurring jet latitude variability. More broadly, these results suggest that thermodynamics (warming and near‐surface stability), not poleward jet shifts, control 21st century Southern Ocean shortwave climate feedbacks. Key Points Sea ice loss (2.6 W m−2) and clouds (1.2 W m−2) explain RCP8.5 absorbed SW changes Southern Ocean radiatively important clouds (RIC) are low‐level liquid clouds RIC respond primarily to warming and stability changes, not poleward jet shifts