Seminar

Abstract

Twenty-five years of large summer cooling over the southeastern United States ending in the mid-1970s coincided with rapidly increasing anthropogenic aerosol emissions. Here, we assess the claim that the cooling in that period was predominantly due to such aerosols. We utilize two 50-member sets of coupled climate model simulations, one with only anthropogenic aerosol forcings and another with all known natural and anthropogenic forcings, together with a long control integration. We show that, in the absence of aerosol forcing, none of the model simulations capture the observed surface cooling rate (~0.56°C/decade), whereas with increasing aerosol emissions two (of fifty) of the simulations do. More importantly, however, we find that the cooling from aerosols (0.20°C/decade) is insufficient to explain the observation. Our results therefore suggest that, while aerosols may have played a role, the observed cooling was a rare event that contained a large contribution from unforced internal variability.

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Antara Banerjee is a Postdoctoral Research Scientist at Columbia University working with Prof. Lorenzo Polvani. Her research includes chemistry-climate interactions, stratosphere-troposphere interactions, climate change and variability, and climate modeling. She received her PhD in 2015 at Cambridge University, UK, where she investigated the climate effects of stratospheric and tropospheric ozone and its role as a surface pollutant.