Abstract
The COVID19 pandemic led to dramatic changes in economic activity in
2020. We use estimates of emissions changes for 2020 in two Earth System
Models (ESMs) to simulate the impacts of the COVID19 economic changes.
Ensembles of nudged simulations are used to separate small signals from
meteorological variability. Reductions in aerosol and precursor
emissions, chiefly Black Carbon (BC) and sulfate (SO$_4$), led to
reductions in total anthropogenic aerosol cooling through aerosol-cloud
interactions. The average overall Effective Radiative Forcing (ERF)
peaks at +0.29$\pm$0.15 Wm$^{-2}$ in spring
2020. Changes in cloud properties are smaller than observed changes
during 2020. Impacts of these changes on regional land surface
temperature range up to +0.3K. The peak impact of these aerosol changes
on global surface temperature is very small (+0.03K). However, the
aerosol changes are the largest contribution to COVID19 emissions
induced radiative forcing and temperature changes, dominating ozone,
CO$_2$ and contrail effects.