The role of anthropogenic aerosol in near-term climate change

Anthropogenic aerosol emissions are expected to change rapidly over the coming decades, with complex geographical and seasonal patterns. This is expected to drive strong, spatially varying trends in temperature, hydroclimate, and extreme events, both near and far from emission sources. These changes are poorly constrained in current models, and very sparsely represented in climate risk assessments, partly because of a lack of dedicated emission pathways and multi-model investigations.

I will start this talk with a whistle stop tour of some of the aspects of the climate system influenced by aerosol changes, including the Atlantic Meridional Overturning Circulation, the monsoons, fire emissions, and climate extremes. I will then introduce the Regional Aerosol Model Intercomparison Project (RAMIP), which is designed to quantify and bound the role of regional aerosol emission changes in near-term climate projections. RAMIP experiments are based on the SSPs commonly used in CMIP6 Endorsed MIPs, but are designed to explore sensitivities to aerosol type and location, and provide improved constraints on uncertainties driven by aerosol radiative forcing and the dynamical response to aerosol changes. The core experiments assess the effects of different aerosol emission pathways in East Asia, South Asia, Africa and the Middle East, and North America and Europe through 2051, using a multi-ensemble-member approach in a set of 10 Earth System Models.