Acceleration by aerosol of a radiative-thermodynamic cloud feedback influencing Arctic surface warming

Recent work suggests that short-lived pollutants with mid-latitude origins are contributing to observed warming of the Arctic surface. Candidate mechanisms include an ‘‘aerosol indirect effect’’ associated with increases in cloud longwave emissivity: small cloud droplets associated with polluted conditions are efficient absorbers and emitters of longwave radiation. Here, we argue that the associated surface warming can be temporarily amplified: particulate pollution, by increasing cloud emissivity, additionally accelerates a preexisting positive feedback loop between cloud top radiative cooling and new droplet condensation.