Abstract

Aerosol presents a large source of uncertainty in climate simulations. It is important to gauge which aspects of aerosol-climate interaction contribute to uncertainty to enable effort to be prioritized, and to constrain uncertainty to facilitate sound decisions on future policy.

We show that climate models with a representation of the indirect effect of aerosol better reproduce inter-decadal variability in historical global-mean near-surface temperatures compared to models representing the direct effect only. Analysis of single forcing runs from CMIP5 shows that the mid-20th century temperature hiatus is likely to have been influenced strongly by anthropogenic aerosol forcing.

As well as global impacts, aerosol can have a pronounced influence on local climate. Using case studies of regions that have large responses to aerosol forcing, we investigate the sensitivity of atmospheric metrics to aerosol changes. We find a large range of sensitivities to aerosol perturbations, as well as considerable differences in the mass loading of some species. This inter-model diversity can produce substantial variation in simulations of climate variability on multi-decadal timescales.