How the strength of the low cloud cover feedback can impact centennial to millennial processes in the climate system

The spread in equilibrium climate sensitivity (ECS) across climate models is largely attributable to variability in their low cloud feedback strength. By systematically varying the strength of the low cloud cover (LCC) feedback within a given climate model (CESM), Erfani and Burls (2019) explore the regional implications for key features of tropical climate of globally weak versus strong LCC feedback in response to greenhouse gas induced warming. Here we examine the influence of the LCC feedback strength on the transient response of the coupled system in both: 1) abrupt CO₂ doubling simulations run for several millennia to near equilibrium, and 2) historical simulations of 20^th century warming. Both shallow and deep oceanic heat uptake and adjustment, and its coupling with atmospheric circulation through large scale sea surface temperature gradients, play a central role in determining the nature (timescale and spatial structure) of transient adjustment under a range of LCC feedback strengths. Finally, we ask the question can the historical record be used to rule out high LCC feedback strengths?