Anthropogenic aerosol impact on (sub-)tropical precipitation patterns over the past century

The International Commission on Clouds and Precipitation Conference, 2021

Aerosols have an influence on temperature and precipitation on both a regional and global scale and have been observed to have an effect on Earth's energy and water cycle through changes in, for instance, large-scale circulations, radiation patterns and cloud microphysics. The complexity of the aerosol impact on the climate system complicates the quantification of the aerosol signal in the observed climate change. A further challenge arises from similar spatial and temporal trends in greenhouse gas and aerosol emissions, complicating the separation of the two signals. Thus, the attributable greenhouse gas impacts on the climate system for the present day are not analogous to what may be experienced in the future with presumably reduced aerosol emissions due to air quality legislation but continuing (and increasing) emissions of greenhouse gases.

In this study, the impact of anthropogenic aerosol emissions on precipitation in the tropics and subtropics is studied using historical single - and all-forcings simulations from phase 6 of the Coupled Model Intercomparison Project (CMIP6). This is achieved by tracking wet and dry regions from 30°S to 30°N. Each model simulation is split into the wettest and driest third (by ranking the grid boxes) for each month, and a 12-month running mean is calculated to form a time series of the average precipitation over the dry and wet regions, respectively. To investigate a potential impact of the shift in aerosol macro-emission regions from North America and Europe to South East Asia in the 1970s, we conduct the analyses from the beginning of the twentieth century until the end of the historical simulations in 2014. 

We find that the historical (all-forcings) runs display a strengthening in the contrast between wet and dry regions, with the wet becoming wetter and the dry becoming drier. Looking at single-forcing runs for anthropogenic greenhouse gases and aerosols, we find inter-model agreement on aerosol induced drying of the wet regions, with a contrasting wetting related to greenhouse gases during the twentieth century, thus, suggesting that some of the greenhouse gas induced increase of precipitation in the wet regions has been offset by aerosol emissions. While a drying of the dry regions is observed in the greenhouse gas-only runs, a trend is not found for aerosols. Natural forcings simulations show a marked, temporary decrease in precipitation in the wet regions following the 1991 eruption of Mount Pinatubo

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How to cite: Roesch, C., Schurer, A., Ballinger, A. and Hegerl, G.: Anthropogenic aerosol impact on (sub-)tropical precipitation patterns over the past century, The International Commission on Clouds and Precipitation Conference, 02-06 Aug 2021,