## 3 Results
### MERRA-2 GDB (SSR Trends) and Its Evaluation
#### 3.2.2 The MERRA-2 GDB on Global, Hemispherical and Regional Scales
Specifically, over the NH land, solar brightening took place during 1980-1999, followed by a dimming during  
Figure 12: Timeseries of MERRA-2 average global (black line) and hemispherical (NH and SH, red and green lines) monthly mean deseasonalized SSR anomalies for the period January 1980–December 2019. Linear regression fit line, along with the associated \(\Delta\)(SSR) for the Globe and the two hemispheres (numbers in the embedded panel), as well as the 4 th-order polynomial fit applied to the global time series of MERRA-2 SSR, are also shown. 2000-2009 and 2010-2019. Over the global oceans, dimming persisted from 1980 to 2009, followed by a subsequent brightening from 2010 to 2019. It is found that, in general, but especially over oceans and the Southern Hemisphere, the magnitude of GDB is larger during the 20 th century (1980-1999) than during the 21 st century (2000-2019), which may be related to the assimilation of contemporary satellite data, such as MODIS, in the MERRA-2 Reanalysis. This change may point to a probably overestimated magnitude of GDB in this study estimated based on MERRA-2. It should be noted that in the NH the MERRA-2 brightening phase of 2010-2019 and the dimming in 2000-2009 harmonize with the stronger global warming (+0.47 \({}^{\circ}\)C decade\({}^{-1}\)) recorded in the second decade of the 21 st century and the weaker warming (+0.16 \({}^{\circ}\)C decade\({}^{-1}\)) observed in the first decade [105]. Furthermore, it should be noted that the MERRA-2 dimming during the 1980s and 1990s may have resulted in a slower rate of NH warming in this period (+0.2 \({}^{\circ}\)C decade\({}^{-1}\)) than in the 2010s when a brightening occurred. Moreover, it is found that the brightening phases during 1980-1999 and 2010-2019, and the dimming in 2000-2009, over the land areas of the globe match with the rapid warming in the 1980s, 1990s and 2010s and the recent hiatus in the 2000s. These results indicate that the MERRA-2 GDB phases are in line with the NH warming rates, since brightening/dimming accelerates/decelerates warming. However, this is not valid when looking at the NH land and ocean areas separately, since the MERRA-2 dimming over NH land in 2010-2019 is not in line with the strong warming (+0.46 \({}^{\circ}\)C decade\({}^{-1}\)) during this period. On the other hand, in the SH, there is no clear relationship between the MERRA-2 GDB phases and the recorded warming rates. These results, which underline the role of GDB for the global temperatures in relation with the greenhouse warming, corroborate the findings of [11], who using the 2-m temperature dataset from the Climate Research Unit of the University of East Anglia (HadCRUT4 (Hadley Centre of the UK Met Office by the Climatic Research Unit)), suggested that in the polluted NH, during the dimming phase in the period 1950s-1980s, which was characterized by a strong increase of aerosol loadings, no warming has been observed, while during the subsequent brightening phase (1980s-2000s) characterized by decreasing aerosol loadings, a rapid warming was observed. In contrast, in the more pristine SH, where greenhouse-gases is the sole major anthropogenic forcing, warming is observed during both dimming and brightening phases. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**AGSR \(\pm\) S.E. ** & **January** & **January** & **January** & **January** \\
**(W/m\({}^{3}\))** & **1980–December 2019** & **1980–December 1999** & **2000–December 2009** & **2010–December 2019** \\ \hline Globe & \(-\)6.31\(\pm\) 0.19 & \(-\)3.64 \(\pm\) 0.31 & \(-\)1.19 \(\pm\) 0.26 & 0.44 \(\pm\) 0.24 \\ \hline N.H. & \(-\)5.72 \(\pm\) 0.28 & \(-\)1.64 \(\pm\) 0.35 & \(-\)1.92 \(\pm\) 0.35 & 0.39 \(\pm\) 0.37 \\ \hline S.H.