Investigating the Relationship between Convective Precipitation Efficiency and Surface Temperature

The CMIP5 inter-model spread of equilibrium climate sensitivity ranges from 2.1 to 4.7 K. Recent studies noted that differences in the treatment of convective precipitation efficiency (CPE) – specifically the autoconversion rate for clouds to form rain – contribute to the large inter-model spread (e.g. Zhao et al 2015). Current convective parameterization schemes in state-of-the-art climate models carry a constant CPE, though the value can vary significantly from one model to the other. Mauritsen and Stevens (2015) showed that a temperature-dependent CPE increases hydrological sensitivity and produces negative cloud and water vapor feedbacks in the ECHAM6 model, and reduced the climate sensitivity. On the other hand, Li et al. (2019) showed that the same modification in the CESM model, due to a positive “iris” feedback associated with optically thinner ice clouds, resulted in a higher climate sensitivity. To better understand this apparent inconsistency between climate models, we investigate the potential dependence of CPE on temperature with convective self-aggregations simulations using System for Atmospheric Modeling.