Abstract
An outstanding question in climate science is how much the change in tropical anvil cloud clover with warming influences Earth's climate sensitivity. Here, we construct a simple model of cloud radiative effects to obtain an analytical equation for the tropical anvil area “iris” feedback. Our equation shows how the feedback is constrained by the fractional change in anvil cloud area, the anvil cloud radiative effect, and the radiative masking of low clouds that live beneath anvils.  We then look at satellite observations to diagnose these quantities. We find that the inferred values of anvil cloud radiative effect and low cloud masking effects sum to 1 Wm-2. Owing to this small radiative effect, the observed changes in anvil cloud cover in interannual variability implies an iris feedback that is wholly insufficient to strongly influence climate sensitivity. We then extend our equation to address whether anvil clouds might affect climate sensitivity through their masking of other forcings  or feedbacks.
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