Interpreting Differences in Radiative Feedbacks from Aerosols Versus
Greenhouse Gases
Abstract
Experiments with six CMIP6 models were used to assess the climate
feedback parameter for net historical, historical greenhouse gas (GHG)
and anthropogenic aerosol forcings. The net radiative feedback is found
to be more amplifying (higher effective climate sensitivity) for aerosol
than GHG forcing, and hence also more amplifying for net historical (GHG
+ aerosol) than GHG only. We demonstrate that this difference is
consistent with their different latitudinal distributions. Historical
aerosol forcing is most pronounced in northern extratropics, where the
boundary layer is decoupled from the free troposphere, so the consequent
temperature change is confined to low altitude and causes low-level
cloud changes. This is caused by change in stability which also affects
upper-tropospheric clearsky emission, both affecting shortwave and
longwave radiative feedbacks. This response is a feature of
extratropical forcing generally, regardless of its sign or hemisphere.