Fast responses on pre-industrial climate from present-day aerosols in a CMIP6 multi-model study

Abstract

Abstract. In this work, we use Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations from 10 Earth system models (ESMs) and general circulation models (GCMs) to study the fast climate responses on pre-industrial climate, due to present-day aerosols. All models carried out two sets of simulations: a control experiment with all forcings set to the year 1850 and a perturbation experiment with all forcings identical to the control, except for aerosols with precursor emissions set to the year 2014. In response to the pattern of all aerosols effective radiative forcing (ERF), the fast temperature responses are characterized by cooling over the continental areas, especially in the Northern Hemisphere, with the largest cooling over East Asia and India, sulfate being the dominant aerosol surface temperature driver for present-day emissions. In the Arctic there is a warming signal for winter in the ensemble mean of fast temperature responses, but the model-to-model variability is large, and it is presumably linked to aerosol-induced circulation changes. The largest fast precipitation responses are seen in the tropical belt regions, generally characterized by a reduction over continental regions and presumably a southward shift of the tropical rain belt. This is a characteristic and robust feature among most models in this study, associated with weakening of the monsoon systems around the globe (Asia, Africa and America) in response to hemispherically asymmetric cooling from a Northern Hemisphere aerosol perturbation, forcing possibly the Intertropical Convergence Zone (ITCZ) and tropical precipitation to shift away from the cooled hemisphere despite that aerosols' effects on temperature and precipitation are only partly realized in these simulations as the sea surface temperatures are kept fixed. An interesting feature in aerosol-induced circulation changes is a characteristic dipole pattern with intensification of the Icelandic Low and an anticyclonic anomaly over southeastern Europe, inducing warm air advection towards the northern polar latitudes in winter.

Climate and air quality impacts due to mitigation of non-methane near-term climate forcers

“…Furthermore, studies show that the hemispheric contrast in aerosol forcing has shifted the tropical rainbelt southward, which is associated with a weakening of the west African monsoon and the occurrence of the Sahel drought of the mid-1980s (Rotstayn and Lohmann, 2002;Biasutti and Giannini, 2006;Allen and Sherwood, 2011;Ackerley et al, 2011;Chang et al, 2011;Biasutti, 2013;Hwang et al, 2013;Dong et al, 2014;Allen et al, 2015;Undorf et al, 2018). The observed precipitation decrease during recent decades over most of the areas affected by the south and east Asian monsoon can also be explained by the dominance of aerosol radiative effects suppressing precipitation over the expected precipitation enhancement due to increased GHGs (Wang et al, 2013;Song et al, 2014;Li et al, 2015;Xie et al, 2016;Krishnan et al, 2016;Guo et al, 2016;Lau and Kim, 2017;Zhang et al, 2017;Lin et al, 2018;Liu et al, 2018).…”

The Dependence of Aerosols’ Global and Local Precipitation Impacts on Emitting Region

“…Tropical regions, which also tend to have the greatest societal vulnerability to precipitation disruption, are the most susceptible to dynamically-driven precipitation changes generated by both local and remote aerosol emissions, as has been highlighted elsewhere (e.g. Scannell et al, 2019;Westervelt et al, 2018;Zanis et al, 2020). However, these regions are also for the precipitation stability of vulnerable regions outside of key past or projected emissions hotspots.…”

Comment on acp-2022-422

“…Future aerosol emissions reductions could greatly aggravate the warming effect caused by greenhouse gas (GHG) forcing (Lin et al, 2016;Hienola et al, 2018), particularly in eastern and southern Asia, and may increase surface temperatures by 0.5°C in some regions (Westervelt et al, 2015;Chuwah et al, 2016) and cause a significant increase in extreme high-temperature events (Wang et al, 2016;Samset et al, 2018;Luo et al, 2020). Future aerosol reductions may also shift the tropical rain belt northwards, enhancing precipitation in the Asian monsoon region (Westervelt et al, 2018;Zanis et al, 2020) and shifting both the mean and extreme values of precipitation toward larger values (Zhao et al, 2018). Asia is a region where extreme precipitation is particularly sensitive to aerosol reductions (Lin et al, 2016;Samset et al, 2018).…”

“…However, few studies in this field have been conducted to date. A recent study considering emissions reductions of aerosols, ozone, and their precursors showed that future non-methane SLCF reductions will not only improve air quality but also increase global mean temperature, precipitation, and climate extremes in the mid-21st century, with more marked warming and wetting trends in some regions, particularly Asia and the Arctic (Allen et al, 2020). However, that study focused on trends of climate variables, and its assessment of regional climate changes, particularly climate extremes, was insufficient.…”