Fast and slow responses of surface air temperature in China to short-lived climate forcers.

Short-lived climate forcers (SLCFs), including aerosols, tropospheric ozone, and methane in this work, are attracting increasing attention because of their extensive impacts on regional climate and air pollution. To clarify the impact of controlling SLCFs in high-emission areas on regional surface air temperature (SAT), we quantified the SAT response in China due to both global and China's SLCF changes by using an aerosol-climate model. The average SAT response in China to global SLCF changes from 1850 to 2014 was -2.53 °C ± 0.52 °C, which was much stronger than the global mean SAT response (-1.85 °C ± 0.15 °C). There are two cooling centers in China, located in the northwest inland areas (NW) and southeastern areas (SE), with area mean SAT responses of -3.39 °C ± 0.70 °C and -2.43 °C ± 0.62 °C, respectively. Because the SE area has experienced greater changes in SLCFs concentrations, compared with the NW area, China's SLCFs contribute more to the SAT response in the SE (approximately 42 %) than to the SAT response in the NW (<25 %). We divided the SAT response into fast and slow components to investigate the underlying mechanisms. In the fast response, the strength of the regional SAT response was closely connected to changes in the SLCFs concentration. The prominent increase in SLCFs in the SE area reduced the surface net radiation flux (NRF), thereby decreasing the SAT by 0.44 °C ± 0.47 °C. The smaller increase in SLCFs in the NW area, compared with the SE area, resulted in a less reduction in NRF and a minor fast SAT response (-0.01 °C ± 0.76 °C). In the slow response, the SLCFs-induced increases of mid- and low-cloud cover significantly reduced the NRF, resulting in strong slow SAT responses of -3.38 °C ± 0.70 °C and -1.98 °C ± 0.62 °C in the NW and SE areas, respectively.