## 4 Conclusions
In contrast, statistically significant dimming is found over the western Tropical Warm Pool, India, Southern East China, Amazonia, stratocumulus covered marine areas off the western coasts of Africa and America and some parts of oceans. * Globally, MERRA-2 SSR shows a dimming (decreasing SSR) from 1980 to 2019, equal to \(-\)6.31 \(\pm\) 0.19 W/m\({}^{2}\) or \(-\)0.158 \(\pm\) 0.005 W/m\({}^{2}\)/year, with 62.8% of the global MERRA-2 geographic cells showing dimming. This dimming is found over both land and ocean areas of the globe, but oceans underwent a stronger dimming (\(-\)7.81 \(\pm\) 0.25 W/m\({}^{2}\) or \(-\)0.195 \(\pm\) 0.006 W/m\({}^{2}\)/year) than land (\(-\)2.58 \(\pm\) 0.25 W/m\({}^{2}\) or \(-\)0.065 \(\pm\) 0.006 W/m\({}^{2}\)/year). Solar dimming also occurred on hemispherical basis, being stronger in the Southern than Northern Hemisphere (\(-\)5.72 \(\pm\) 0.28 W/m\({}^{2}\) versus \(-\)6.16 \(\pm\) 0.38 W/m\({}^{2}\) or \(-\)0.143 \(\pm\) 0.007 W/m\({}^{2}\)/year versus \(-\)0.154 \(\pm\) 0.01 W/m\({}^{2}\)/year, respectively). * Examining possible changes of the agreement between the signs of GDB of GEBA stations and MERRA-2 with time, an improvement is found since 1985, and especially in the post-2000 period, which can be related to the assimilation of state-of-the-art satellite data (MODIS, MISR) in MERRA-2 after 2000. * During the reported brightening in the literature in the 1980s and 1990s, MERRA-2 reproduces brightening only over land, which is in line with the rapid global warming in the North Hemisphere driven by anthropogenic greenhouse gases. In the 2000s, when a recent hiatus has been recorded, MERRA-2 indicates a dimming both on a global basis (\(-\)1.19 \(\pm\) 0.26 W/m\({}^{2}\) or \(-\)0.119 \(\pm\) 0.026 W/m\({}^{2}\)/year) and on a hemispherical one, which seems to be in line with the deceleration of global warming. In the 2010s, MERRA-2 suggests a weak global brightening (\(+\)0.44 \(\pm\) 0.24 W/m\({}^{2}\) or \(+\)0.044 \(\pm\) 0.024 W/m\({}^{2}\)/year), which is in accord with the recurring accelerated warming of the Globe. Thus, overall, the MERRA-2 GDB phases, especially in the Northern Hemisphere, seem to be consistent with the accelerating and decelerating decadal phases of global warming since 2000. Overall, the present study, based on detailed comparisons against the reference global GEBA and BSRN station networks, documents a quite satisfactory performance of the MERRA-2 SSR, along with a worse performance of MERRA-2 SSR changes during the 40-year period 1980-2019. These results at the Earth's surface are accompanied by a less satisfactory comparison of the corresponding to SSR top of atmosphere solar fluxes of MERRA-2 against reference CERES fluxes. The ascertained performance of MERRA-2 SSR data is encouraging towards their use in various climate studies, but they cannot provide reliable SSR trends and GDB assessment. In conclusion, further improvements to MERRA Reanalysis solar fluxes are necessary, which are, however, worth given the advantages of this Reanalysis, like its complete spatial (global) and long temporal (climatological) coverage and the consideration, for the first time, of aerosol-cloud interactions. With the expected continuation and extension of the MERRA Reanalysis in the time to come, an even longer climatology of SSR will be created, which will enable a better assessment of the climatic role of the GDB phenomenon, especially in relation with the ongoing greenhouse warming. However, such assessments can only be reliable by making additional improvements to the MERRA-2 SSR products.