Cloud Regime Contributions to Recent Changes in Outgoing Radiation: A 22-year Satellite Data Analysis

Using multi-factor ridge regression on 22 years of CERES EBAF data against cloud regime (CR) groups' relative frequencies of occurrence (RFOs), we quantify the CR groups' contributions to global outgoing radiation changes between two decades (2003–2012 vs. 2015–2024), accounting for both changes in RFO and within-CR (internal) cloud properties. For outgoing shortwave radiation (OSR), individual CR group radiative contributions due to within-CR property changes are relatively small. However, consistently negative contributions, stemming primarily from reductions in CR's cloud fraction, result in a notable net negative contribution. Contributions from RFO variations are individually large, but substantial offsets between negative (from the mid and low-thin Lₜn groups) and positive contributions (from the semi-clear S-Clr group) lead to a net negative contribution that is smaller than that from internal changes. Combining both effects, the contributions of low-thin (? 0. 8 Wm? 2) and semi-clear (0. 9 Wm? 2) largely cancel out (due to a transition from Lₜn to S-Clr), leaving the contribution of mid clouds (? 0. 7 Wm? 2) as the primary factor in the total OSR change (? 1. 0 Wm? 2). The decreased RFO of mid-clouds is due to a transition from mid-level to higher-level clouds, consistent with a response to warmer temperatures. For outgoing longwave radiation (OLR), the transition from low-thin to semi-clear provides overwhelmingly large and opposing RFO contributions (? 3. 0 Wm? 2 vs. 3. 7 Wm? 2), leaving a net effect comparable to the total OLR change of 0. 5 Wm? 2. This result suggests a reduced influence of oceanic cumulus on OLR, consistent with a rise in SSTs.