How strong are the links between global warming and surface solar radiation changes?

The aim of this study is to investigate the possible relationship between the recent global warming and the interdecadal changes in incoming surface solar radiation (SSR), known as global dimming and brightening (GDB). The analysis is done on a monthly and annual basis on a global scale for the 35-year period 1984–2018 using surface temperature data from the European Centre for Medium-Range Weather Forecasts (ECMWF) v5 (ERA5) reanalysis and SSR fluxes from the FORTH (Foundation for Research and Technology-Hellas) radiative transfer model (RTM). Our analysis shows that on a monthly basis, SSR is correlated with temperature more strongly over global land than ocean areas. According to the RTM calculations, the SSR increased (inducing brightening) over most land areas during 1984–1999, while this increase leveled-off (causing dimming) in the 2000s and strengthened again in the 2010s. These SSR fluctuations are found to affect the global warming rates. Specifically, during the dimming phase in the 2000s, the warming rates across land areas with intense anthropogenic pollution, like Europe and East Asia, slowed down, while during the brightening phases, in the 1980s, 1990s and 2010s, the warming rates were reinforced. Although the magnitude of GDB and the Earth’s surface warming trends are not proportional, indicating that GDB is not the primary driver of the recent global warming, it seems that GDB can affect the warming rates, partly counterbalancing the dominant greenhouse warming during the dimming or accelerating the greenhouse-induced warming during the brightening phases of GDB.