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Observational quantification of tropical high cloud changes and feedbacks

Presentation Date
Monday, December 11, 2023 at 2:20pm - Monday, December 11, 2023 at 2:30pm
MC - 3004 - West



The response of high cloud properties such as their amount, altitude, and optical depth to surface warming is uncertain. For example, previous studies indicated significant contraction in tropical high cloud cover associated with warming, entailing a stabilizing radiative feedback (iris feedback) for climate. Global satellite observations with passive and active remote sensing capabilities over the last two decades can now be used to address such effects that were previously observationally limited. Here we show that satellite-observed tropical high clouds exhibit no net contraction in their vertical profile and the corresponding amount radiative feedback is near-zero, providing strong evidence against the controversial iris hypotheses. Next, we find that tropical high clouds have risen but have also warmed, leading to a positive but muted altitude feedback. Finally, we find that high clouds have been thinning, leading to a near-zero optical depth feedback. These new high cloud feedback estimates constrain and increase climate sensitivity. A hierarchy of experiments in the Community Earth System Model version 2 show biases relative to these observed feedbacks, implying biases in this ‘hot’ model’s climate sensitivity.

Funding Program Area(s)