Explaining recent cloud radiative effect anomalies and trends in CERES observations

Changes to the top-of-atmosphere cloud radiative effect (CRE) play a crucial role in the Earth's radiation budget, yet its key controls are poorly comprehended. Preliminary results using the latest observational data from CERES EBAF between 2000 and 2019 display several instances of large global CRE anomalies that are puzzlingly of similar magnitude. While in some cases these large anomalies can be tied to El Niño-Southern Oscillation (ENSO) events, in others, they appear not to be associated with this mode of climate variability. Observations from CERES also show a notable decreasing trend in global longwave (LW) CRE and an increasing trend in shortwave (SW) CRE over the two decades. In this presentation, we: 1) investigate the differences between the cloud properties that cause similar globally averaged large CRE anomalies during ENSO and non-ENSO events and 2) understand and diagnose the causes for the decreasing trend in LW CRE and increasing trend in SW CRE. Specifically, we quantify how changes in cloud properties and distribution contribute to CRE anomalies and trends using a GFDL benchmark-calibrated radiative transfer model. We use MODIS, Cloudsat, and CALIPSO observations of cloud fraction, cloud optical depth, and liquid and ice water content to constrain our partial radiation perturbation experiments. We also conduct a set of experiments with GFDL AM4 to study how surface temperature spatial patterns and atmospheric stability contribute to the observed CRE trends. These experiments help elucidate why the net cooling effect of clouds has not changed over this period, i.e., a flat net CRE trend, despite a strong underlying surface warming trend.