The Atmospheric Effect of Aerosols on Future Tropical Cyclone Frequency and Precipitation in the Energy Exascale Earth System Model
There is no consensus on how global tropical cyclone (TC) activity may change in the future. Although future changes in greenhouse gas and aerosol concentrations are typically considered together, they follow different trajectories and can influence TC activity in different ways. We investigated the atmospheric effects of aerosols and the influence of greenhouse gases on TC frequency and precipitation using experiments with the Energy Exascale Earth System Model (E3SM). We found that future changes in greenhouse gas and aerosol concentrations can drive counteracting regional changes in TC frequency. In addition, we found that while both forcings enhance TC precipitation, increased greenhouse gases preferentially enhance TC precipitation in the inner-core, whereas decreased aerosols lead to TC precipitation decreases in the inner-core and increases in the outer-bands.
This research highlights the importance of proper representation of the spatial distribution of aerosols when studying future projections of tropical cyclone frequency and precipitation.
This study uses experiments from the Energy Exascale Earth System Model (E3SM) to compare the influence on tropical cyclone (TC) activity of: i) the atmospheric effect of aerosols under specified sea-surface temperatures (SSTs) and ii) the net effect of greenhouse gases (GhGs) including changes in SSTs. The experiments were performed using the CMIP6 Shared Socioeconomic Pathway SSP5-8.5 emissions scenario with GhG induced SST warming specified and atmospheric aerosol effects simulated but without explicit ocean coupling. Insignificant changes in global TC frequency were found in response to the atmospheric effect of future aerosols and GhGs, as significant regional responses in TC frequency counteract each other. Future GhGs contribute to more frequent TCs in the North Atlantic, and reductions over the Northwestern Pacific and Southern Indian Ocean. The atmospheric effect of future aerosols drives more frequent TCs over the Northwestern Pacific and reductions over the Northeast Pacific and North Atlantic. Along with increases in TC intensity, global TC precipitation (TCP) is projected to increase by 52.8% (14.1%/K) due to the combined effect of future aerosols and GhGs. Although both forcings contribute to TCP increases (14.7-19.3% from reduced aerosols alone and 28.1-33.3% from increased GhGs alone), they lead to different responses in the spatial structure of TCP. TCP increases preferentially in the inner-core due to increased GhGs, whereas TCP decreases in the inner-core and increases in the outer-bands in response to the atmospheric effects of decreased aerosols. These changes are distinct from those caused by aerosol-induced SST changes, which have been considered in other studies.