Distinct climate responses to regional aerosol emissions

Anthropogenic aerosol emissions have had a major influence on global climate over the industrial era, counteracting some of the warming and precipitation increases due to rising greenhouse gas concentrations. These greenhouse gas driven changes are now rapidly being unmasked, through a range of national and regional policies aimed at improving air quality. However, unlike greenhouse gases, aerosol emissions have strongly regional response patterns, and influence the climate both near to, and far from emission sources. These regional influences have to date not been quantified in a consistent, multi-model framework.

Here, we present results from the Regional Aerosol Model Intercomparison Project (RAMIP). Ten CMIP6 era models have performed 10- member ensemble simulations investigating the climate response to aerosol emissions, separately, from South Asia, East Asia, Africa and the Middle East, and Europe and North America. All RAMIP experiments are based on two CMIP6-era SSPs: SSP3-7.0 (strong GHG increases, minimal aerosol reductions) and a hybrid SSP370-126aer (anthropogenic emissions of SO2, organic carbon, and black carbon are rapidly reduced following SSP1-2.6, either globally or regionally).

We find a rapid surface warming in response to aerosol reductions, and strong precipitation increases, but with marked regional differences in the magnitude of the response. While there are many robust responses, strong inter-model differences in the pattern and strength of the responses in some regions highlights where aerosol related uncertainty is large in the near-future.

We discuss the linearity of the effective radiative forcing and climate responses from regional aerosol perturbations, and demonstrate that emission location is key to the amplitude and extent of the response. In particular, emission changes in East Asia and North America and Europe have a larger global temperature impact than those over South Asia due to their influence on Pacific clouds. This initial analysis demonstrates the need for aerosol awareness in the design of future scenario ensembles, and in climate risk and impact studies both near to and far from aerosol emission sources.