Climate influences of Asian anthropogenic aerosols decomposed using a Reduced Complexity Model

Aerosol emissions have a wide range of impacts on the climate both near to and far from emission sources. Impacts span from local changes in surface solar warming to large-scale modifications of atmospheric circulation patterns and monsoonal precipitation. They have also been found to have an outsized near-term influence on extreme events in recent climate model studies. Consequently, future aerosol emission changes are likely to contribute to climate related risk in many highly populated regions, some of which are particularly vulnerable, for instance, to shifts in precipitation patterns or timing with respect to growing seasons. However, aerosol climate impacts generally follow patterns and time evolutions that are markedly different to those from greenhouse gas driven global surface warming, and our understanding of them is still plagued by high scientific uncertainty.

Given the urgent need for improved knowledge about the near-term influences of changes in aerosol emissions, we here introduce SyRAP-FORTE – a tool for understanding and decomposing the local and remote climate effects of regional aerosol emissions. SyRAP – a set of Systematic Regional Aerosol Perturbations – is developed using FORTE2.0, a Reduced Complexity (RC) climate model developed in the UK. Current and expected future aerosol emission changes are particularly strong in East and South Asia, where high population densities imply high potential climate risk. In the initial version of SyRAP, presented here, we therefore perturb absorbing and scattering aerosols, separately, over India and East China, to assess their separate influence on local responses in a range of climate parameters.

We document and validate the climate responses in FORTE to the regional aerosol perturbations, showing for instance that removing emissions of absorbing aerosols over both East China and will cause a local drying, but a range of more widespread effects. We find that SyRAP is able to reproduce the overall aerosol responses documented in the literature, and also that it allows us to decompose the influences of different aerosol species from the two regions on the climate near to, and far from, the emission sources.

Finally, we show how SyRAP can be used as input to emulators and tunable simple climate models, and as a ready-made tool for projecting the effects of near-term changes in Asian aerosol emissions.