Minimal climate impacts from short-lived climate forcers following
emission reductions related to the COVID-19 pandemic.
We present an assessment of the impacts on atmospheric composition and
radiative forcing of short-lived pollutants following worldwide decrease
in anthropogenic activity and emissions comparable to what has occurred
in response to the COVID-19 pandemic, using the global
composition-climate model UKCA. Changes in emissions reduce tropospheric
hydroxyl radical and ozone burdens, increasing methane lifetime. Reduced
SO emissions and oxidising capacity lead to a decrease in the sulphate
aerosol burden and increase in aerosol particle size, with accompanying
reductions to cloud droplet number concentration. However, large
reductions in black carbon emissions increase the albedo of aerosols.
Overall, the changes in ozone and aerosol direct effects (neglecting
aerosol-cloud interactions) result in an instantaneous radiative forcing
of -31 to -74 mWm. Upon cessation of emission reductions the
short-lived climate forcers rapidly return to pre-COVID levels, meaning
these changes are unlikely to have lasting impacts on climate assuming
emissions return to pre-intervention levels.