Variations of Siberian High Position under climate change: Impacts on winter pollution over north China

We examined the correlations between winter aerosol optical depth (AOD) in North China (NC) and three synoptic-scale meteorological indices from 2001 to 2016, including the Siberian High intensity (SHI), East Asian Winter Monsoon intensity (EAWMI), and the Siberian High Position index (SHPI). To separate the influences from meteorology and emissions, NC AOD was detrended by subtracting a linear increasing trend from 2001 to 2013 and a decreasing trend from 2014 to 2016, in correspondence with reported changes in Chinese anthropogenic emissions during the same period. The SHPI explains 37% of the variability in the detrended NC AOD and 83% of the high SHPI winters correspond to high AOD. By contrast, the SHI and EAWMI show little correlation with the observed AOD variability. To project the SHPI in the future climate, we used the ensemble of six global circulation models (GCMs) which were found capable of reproducing the climatic spatial distribution and the longitudinal variability of the Siberian High from 1956 to 2005. The ensemble results show that the frequency of high SHPI winters and consequently more polluted conditions would increase by 29%, 61%, and 100% under RCP2.6, RCP4.5 and RCP8.5 until 2099. There are 11 out of the 25 GCMs examined here that project the possibility of high SHPI conditions to increase under RCP8.5. This indicates changes in the Siberian High position induced by increasing global greenhouse gas (GHG) emissions can lead to more winter pollution in North China in the future.