ABSTRACT
In order to know how surface air temperature (SAT) changes in East Asia under different emission scenarios after the COVID-19 outbreak, in this paper, we investigated the impacts of greenhouse gases (GHGs) and anthropogenic aerosols changes on SAT in East Asia by using the aerosol-climate coupled model BCC-AGCM 2.0_CUACE/Aero, combining with the post-pandemic emission scenarios proposed by Covid multi-Earth system model intercomparison project (CovidMIP scenarios for short, including fossil-fueled recovery, moderate green stimulus, strong green stimulus, hereinafter as FFF, MGG, SGG, respectively). We assessed the impacts of changes in GHGs and anthropogenic aerosols together and separately on SAT in East Asia and its typical subregions during 2020‒2050. The results show that by mid-21st-century, SAT in East Asia will increase by 0.81±0.083°C under Baseline (same as SSP2-4.5 scenario), i.e., SAT difference between 2045‒2050 and 2020‒2025), and there will be more intense warming in all the three scenarios in East Asia, in which the largest SAT difference (SAT-d) compared to Baseline is 0.33±0.11°C under SGG and the smallest SAT-d is 0.07±0.14°C under FFF. To further explore the mechanism of these SAT-d, we analyzed the trend of surface longwave and shortwave net radiation flux driven by GHGs and anthropogenic aerosols there. It is found that in early period (2020‒2035), the role of aerosol changes is bigger than that of GHG changes in dominating SAT-d, particularly sulfate, whose reduction will become the main contributor to SAT-d by affecting the net solar flux at surface. In later period (2036‒2050), because of GHGs’ longer atmospheric lifetime than aerosols, the role of decreasing GHGs concentrations will determine the drop in SAT-d through affecting the net longwave flux at surface.
ABSTRACT
With the continuation of the Coronavirus Disease 2019 (Covid-19) pandemic, the impacts of this catastrophe on anthropogenic emissions are no longer limited to its early stage. This study quantitatively estimates effective radiative forcings (ERFs) due to anthropogenic well-mixed greenhouse gases (WMGHGs) and aerosols for the period 2020-2050 under the three latest Covid-19 economic-recovery scenarios using an aerosol-climate model. The results indicate that reductions in both WMGHG and aerosol emissions under the Covid-19 green recoveries lead to increases ranging from 0 to 0.3 W m-2 in global annual mean anthropogenic ERF over the period 2020-2050 relative to the Shared Socioeconomic Pathway 2-4.5 scenario (the baseline case). These positive ERFs are mainly attributed to the rapid and dramatic decreases in atmospheric aerosol content that increase net shortwave radiative flux at the top of atmosphere via weakening the direct aerosol effect and low cloud cover. At the regional scale, reductions in aerosols contribute to positive ERFs throughout the Northern Hemisphere, while the decreased WMGHGs dominate negative ERFs over the areas away from aerosol pollution, such as the Southern Hemisphere oceans. This drives a strong interhemispheric contrast of ERFs. In contrast, the increased anthropogenic emissions under the fossil-fueled recovery scenario lead to an increase of 0.3 W m-2 in global annual mean ERF in 2050 compared with the baseline case, primarily due to the contribution of WMGHG ERFs. The regional ERF changes are highly dependent on local cloud radiative effects.