Local and remote mean and extreme temperature response to regional aerosol emissions reductions

Abstract

Abstract. The climatic implications of regional aerosol and precursor emissions reductions implemented to protect human health are poorly understood. We investigate the mean and extreme temperature response to regional changes in aerosol emissions using three coupled chemistry–climate models: NOAA GFDL CM3, NCAR CESM1, and NASA GISS-E2. Our approach contrasts a long present-day control simulation from each model (up to 400 years with perpetual year 2000 or 2005 emissions) with 14 individual aerosol emissions perturbation simulations (160–240 years each). We perturb emissions of sulfur dioxide (SO2) and/or carbonaceous aerosol within six world regions and assess the statistical significance of mean and extreme temperature responses relative to internal variability determined by the control simulation and across the models. In all models, the global mean surface temperature response (perturbation minus control) to SO2 and/or carbonaceous aerosol is mostly positive (warming) and statistically significant and ranges from +0.17 K (Europe SO2) to −0.06 K (US BC). The warming response to SO2 reductions is strongest in the US and Europe perturbation simulations, both globally and regionally, with Arctic warming up to 1 K due to a removal of European anthropogenic SO2 emissions alone; however, even emissions from regions remote to the Arctic, such as SO2 from India, significantly warm the Arctic by up to 0.5 K. Arctic warming is the most robust response across each model and several aerosol emissions perturbations. The temperature response in the Northern Hemisphere midlatitudes is most sensitive to emissions perturbations within that region. In the tropics, however, the temperature response to emissions perturbations is roughly the same in magnitude as emissions perturbations either within or outside of the tropics. We find that climate sensitivity to regional aerosol perturbations ranges from 0.5 to 1.0 K (W m−2)−1 depending on the region and aerosol composition and is larger than the climate sensitivity to a doubling of CO2 in two of three models. We update previous estimates of regional temperature potential (RTP), a metric for estimating the regional temperature responses to a regional emissions perturbation that can facilitate assessment of climate impacts with integrated assessment models without requiring computationally demanding coupled climate model simulations. These calculations indicate a robust regional response to aerosol forcing within the Northern Hemisphere midlatitudes, regardless of where the aerosol forcing is located longitudinally. We show that regional aerosol perturbations can significantly increase extreme temperatures on the regional scale. Except in the Arctic in the summer, extreme temperature responses largely mirror mean temperature responses to regional aerosol perturbations through a shift of the temperature distributions and are mostly dominated by local rather than remote aerosol forcing.

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

“…6). This result is consistent with recent studies showing high Arctic sensitivity to aerosol reductions (Acosta Navarro et al, 2016;Lewinschal et al, 2019;Westervelt et al, 2020). Other latitudinal bands also significantly warm, including the NH midlatitudes (30-60 • N), tropics (30 • S-30 • N), and Southern Hemisphere (SH) midlatitudes (60-30 • S) at 0.10 ± 0.03, 0.05 ± 0.01, and 0.03 ± 0.02 K decade −1 , respectively.…”

How Asian aerosols impact regional surface temperatures across the globe

“…Aerosols give rise to both local and remote temperature responses, so that the geographic distributions of aerosol radiative forcing and temperature effects are largely dislocated (Shindell et al, 2010;Nordling at al., 2019). Furthermore, the same aerosol emissions originating from different regions vary in their climate forcing efficacies, with their global surface temperature response per unit global radiative forcing differing by factors of between 2 and 14, depending on aerosols species and the models used (Kasoar et al, 2018;Westervelt, et al, 2020;Persad and Caldeira, 2018).…”

“…The authors pinpointed the mixed results from the models to their different treatments of aerosol microphysical processes and aerosolcloud interactions. Westervelt et al (2020) also used three climate models (GFDL, CESM1, and GISS-E2) to investigate the surface temperature responses to the removals (or significant reductions) of aerosol sources from several different regions, including China and India. Overall, the models varied in aerosol radiative forcings and regional temperature response patterns associated with Asian aerosol reductions but suggested that the reductions mostly result in a significant surface temperature increase across the Northern Hemisphere and particularly over the Arctic.…”

Relative Importance of Greenhouse Gases, Sulfate, Organic Carbon, and Black Carbon Aerosol for South Asian Monsoon Rainfall Changes

“…Aerosol extinction of incoming solar radiation via direct and indirect effects results in weaker precipitation due to weakened circulation (Li et al, 2019;Ramanathan et al, 2001;Singh, 2016). Aerosol emissions and thus forcing are also spatially heterogeneous both zonally and meridionally, which can result in further enhancement of the circulation (dynamic) component of the precipitation response (Li et al, 2018;Shen & Zhao, 2020;Westervelt et al, 2017Westervelt et al, , 2018Westervelt et al, , 2020. Research has also shown that the fast response (using fixed SST) dominates the total aerosol-induced monsoon changes but that SST feedbacks are more important for the GHG-forced response (Li et al, 2018).…”