Abstract
Abstract. South and East Asian anthropogenic aerosols mostly reside in an air mass extending from the Indian Ocean to the North Pacific. Yet the surface temperature effects of Asian aerosols spread across the whole globe. Here, we remove Asian anthropogenic aerosols from two independent climate models (ECHAM6.1 and NorESM1) using the same representation of aerosols via MACv2-SP (a simple plume implementation of the second version of the Max Planck Institute Aerosol Climatology). We then robustly decompose the global distribution of surface temperature responses into contributions from atmospheric energy flux changes. We find that the horizontal atmospheric energy transport strongly moderates the surface temperature response over the regions where Asian aerosols reside. Atmospheric energy transport and changes in clear-sky longwave radiation redistribute the temperature effects efficiently across the Northern Hemisphere and to a lesser extent also over the Southern Hemisphere. The model-mean global surface temperature response to Asian anthropogenic aerosol removal is 0.26±0.04 ∘C (0.22±0.03 for ECHAM6.1 and 0.30±0.03 ∘C for NorESM1) of warming. Model-to-model differences in global surface temperature response mainly arise from differences in longwave cloud (0.01±0.01 for ECHAM6.1 and 0.05±0.01 ∘C for NorESM1) and shortwave cloud (0.03±0.03 for ECHAM6.1 and 0.07±0.02 ∘C for NorESM1) responses. The differences in cloud responses between the models also dominate the differences in regional temperature responses. In both models, the northern-hemispheric surface warming amplifies towards the Arctic, where the total temperature response is highly seasonal and weakest during the Arctic summer. We estimate that under a strong Asian aerosol mitigation policy tied with strong climate mitigation (Shared Socioeconomic Pathway 1-1.9) the Asian aerosol reductions can add around 8 years' worth of current-day global warming during the next few decades.
Highlights
Understanding how regional climates respond to different climate forcers is crucial for assessing how climate change impacts societies. Samset et al (2018) showed that anthropogenic aerosols cool the global-mean surface temperature in four latest-generation climate models by between 0.5–1.1 K
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)
Note that since we here remove the Asian anthropogenic aerosols from the models, IRF is positive in sign, i.e., that of warming
Summary
Understanding how regional climates respond to different climate forcers is crucial for assessing how climate change impacts societies. Samset et al (2018) showed that anthropogenic aerosols cool the global-mean surface temperature in four latest-generation climate models by between 0.5–1.1 K. The regional impacts of anthropogenic aerosols on surface temperatures remain complicated to unravel (Persad and Caldeira, 2018; Nordling et al, 2019). 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). 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)
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