The response of marine low clouds to increasing greenhouse gases is a leading source of uncertainty in climate sensitivity. Here, we estimate regionally resolved, observationally constrained marine low cloud feedbacks at a near-global scale. Multiple satellite cloud observations are used to estimate the spatially varying sensitivity of low cloud-induced radiative anomalies to local changes in cloud-controlling factors. This permits the first-ever separate quantifications of marine low cloud feedbacks from trade cumulus, subtropical stratocumulus, and middle-latitude low clouds. We infer a positive low cloud feedback in the midlatitudes that is larger than climate models predict as well as a positive stratocumulus feedback and near-zero trade cumulus feedback, consistent with results from large eddy simulations. The observationally constrained positive midlatitude low cloud and subtropical stratocumulus feedbacks each result from reductions in both cloud amount and optical depth in response to increasing sea surface temperature, suggesting a common underlying mechanism for these changes. We conclude that the marine low cloud feedback between 60°S and 60°N is likely positive.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. It is supported by the Regional and Global Model Analysis Program of the Office of Science at the DOE. IM Release #LLNL-ABS-783563.