Abstract
Cloud feedback is the largest uncertainty in estimating Equilibrium
Climate Sensitivity. In this study we focus on the equatorial Pacific,
where CMIP6 model cloud feedback spread is notably large. Cloud
radiative effects in this region are relevant for the global climate.
Our findings show that models predict a consistent shift towards the
ascent regime in response to El Nino-like sea surface warming. Models
diverge in terms of the radiative impact due to differences in cloud
morphology in ascent and subsidence regimes. Using the observed
relationship between circulation regime and cloud radiative effect, we
find a reduction in the regional mean cloud feedback estimate from 0.77
to 0.22 Wm-2K-1, though this does not substantially lessen the model
spread in total feedback. Pathways to reduce this spread include:
improving confidence in the regional ocean warming pattern, and using
observations and models to understand cloud morphology and circulation
interactions.