Quantifying all-sky climate sensitivity with idealized clouds

We include idealised clouds in a single column model to estimate the all-sky climate sensitivity. Our results show that the cloud radiative effects observed from satellites can be accurately reproduced by combining high and low/mid-level clouds. We introduce a "fixed cloud albedo" null hypothesis, which assumes a fixed cloud albedo but allows for changes in cloud temperature as the surface warms. By analysing cloud distributions consistent with present-day observations, we estimate a mean fixed-albedo climate sensitivity of 2.2 K, slightly less than the clear-sky value. Our results highlight the importance of cloud masking effects, especially by mid-level clouds, and the reduction of radiative forcing by high clouds. Giving more weight to low-level clouds, which are assumed to change temperature with warming, results in a reduced estimate of 2.0 K. This provides a baseline to which changes in surface albedo, and a believed reduction in cloud albedo, would add to.