Attribution of Anthropogenic Influence on Atmospheric Patterns Conducive to Recent Most Severe Haze Over Eastern China

Severe haze pollution in eastern China has caused substantial health impacts and economic loss. Conducive atmospheric conditions are important to affect occurrence of severe haze events, and circulation changes induced by future global climate warming are projected to increase the frequency of such events. However, a potential contribution of an anthropogenic influence to recent most severe haze (December 2015 and January 2013) over eastern China remains unclear. Here we show that the anthropogenic influence, which is estimated by using large ensemble runs with a climate model forced with and without anthropogenic forcings, has already increased the probability of the atmospheric patterns conducive to severe haze by at least 45% in January 2013 and 27% in December 2015, respectively. We further confirm that simulated atmospheric circulation pattern changes induced by anthropogenic influence are driven mainly by increased greenhouse gas emissions. Our results suggest that more strict reductions in pollutant emissions are needed under future anthropogenic warming. Plain Language Summary Extremely severe haze pollution occurred in December 2015 and January 2013 over eastern China with concentrations of PM2.5 reaching 500gm(-3). During such severe haze, atmospheric circulation exhibited an anomalous east-west sea level pressure gradient and a weakened East Asia monsoon. We assess in this work the role of anthropogenic climate change in such large-scale circulation anomalies by using a large ensemble of climate simulations forced with and without anthropogenic forcings. Anthropogenic influence is estimated to increase the probability of the occurrence of anomalous atmospheric pattern similar to that in January 2013 (December 2015) by 45% (27%). We further confirm that the simulated anthropogenic circulation changes are induced mainly by increased greenhouse gas emissions. Results from our study suggest that more strict emission reduction measures are needed to improve air quality under a continuing anthropogenic warming in the upcoming decades and global effort to reduce greenhouse gas emissions can decrease the risk of severe haze over eastern China.