Observational constraint on a feedback from supercooled clouds reduces projected warming uncertainty

Abstract The increase of climate sensitivity in the latest Earth system models (ESMs) is primarily attributed to a larger extratropical cloud response to warming. This stronger cloud feedback is thought to be partly driven by a greater ratio of supercooled liquid-phase clouds relative to all clouds, termed liquid phase ratio (LPR). Here we use an instrument simulator approach to show that LPR is actually overestimated in coupled model intercomparison project (CMIP) ESMs rather than underestimated as previously thought. Furthermore, we find that the relationship between LPR and the extratropical cloud feedback is in the opposite direction of what had been shown in previous single-ESM studies. We pinpoint this unexpected result to a previously-undocumented feedback from liquid clouds, which weakens the extratropical cloud contribution to warming. Finally, we present evidence that better constraining LPR in CMIP models will reduce uncertainty in climate projections, owing to this novel extratropical feedback from supercooled clouds.