Precipitation Efficiency Constraint on Climate Change

Precipitation efficiency (PE) relates cloud condensation to precipitation
and intrinsically binds atmospheric circulation to the hydrological cycle.
Due to PE’s inherent microphysical dependencies, definitions and estimates
vary immensely. Consequently, PE’s sensitivity to greenhouse warming and
implications for climate change are poorly understood. Here, we quantify
PE’s role in climate change by defining a simple index as the ratio of
surface precipitation to condensed water path. This macroscopic metric is
reconcilable with microphysical PE measures and higher is associated with
stronger mean Walker circulation. We further find that state-of-the-art
climate models disagree on the sign and magnitude of
future changes. This sign disagreement originates from models’
convective parameterizations. Critically, models with increasing under
greenhouse warming, in line with cloud-resolving simulations, show greater
slowdown of the large-scale Hadley and Walker circulations and a two-fold
greater increase in extreme rainfall than models with decreasing.