Measurement biases explain discrepancies between the observed and simulated decadal variability of surface incident solar radiation

Abstract

Observations have reported a widespread dimming of surface incident solar radiation (R s) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. We find that the decadal variability of observed R s may have important errors due to instrument sensitivity drifting and instrument replacement. While sunshine duration (SunDu), which is a robust measurement related to R s, is nearly free from these problems. We estimate R s from SunDu with a method calibrated by the observed R s at each station. SunDu-derived R s declined over China by-2.8 (with a 95% confidence interval of-1.9 to-3.7) W m -2 per decade from 1960 to 1989, while the observed R s declined by-8.5 (with a 95% confidence interval of-7.3 to-9.8) W m -2 per decade. The former trend was duplicated by some high-quality CMIP5 models, but none reproduced the latter trend.