How Do Differences in the Simulation of Present-Day Clouds Affect Cloud Feedbacks?

Abstract

Cloud radiative feedbacks are currently the largest source of spread in estimates of climate sensitivity. Here, we examine how cloud feedbacks relate to model simulations of present-day clouds relative to NASA Multiangle Imaging SpectroRadiometer (MISR) satellite observations. Specifically, we examine relationships between simulated present-day cloud fraction, cloud top height, and cloud optical depth with tropical high cloud, midlatitude low cloud, global high cloud altitude, and tropical low cloud feedbacks for CMIP5 and CMIP6 models that have produced MISR simulator output. We find that the strength of all four of these simulated cloud feedbacks have statistically significant relationships with simulations of present-day clouds. We use these relationships in an emergent constraint analysis to narrow the spread in the estimated strength of each feedback. This suggests that future expert assessments of cloud feedbacks (and climate sensitivity) should consider the state of present-day clouds and the climate modeling community might consider undertaking simulations where models are systematically tuned to eliminate (or at least reduce) biases relative to satellite observations.