Similarity and disparity in regional climate response between greenhouse gas and aerosol forcing

Spatial distribution is quite distinct between anthropogenic changes in greenhouse gas and aerosols. Regional patterns of climate response bear a striking similarity between the two forcing types, however, due to fast atmospheric adjustments and slow ocean-atmosphere interactions. With strong spatial variations, aerosol forcing is more effective in inducing atmospheric circulation and rainfall response than the greenhouse gas forcing. The opposing polarity and similar pattern in regional response between the two forcing agents suppress historical rainfall change, rendering the detection difficult. A close comparison of single forcing experiments with coupled ocean-atmosphere models reveals substantial differences in climate response to different radiative forcing, especially in the north-south direction. The aerosol forcing, larger in the Northern than Southern Hemispheres, induces an interhemispheric Hadley circulation. From ship observations and reanalyses, we detected a robust change in the zonal mean cross-equatorial wind over the past 60 years, accompanied by physically consistent changes in atmospheric pressure and marine cloud cover. Single-forcing experiments indicate that the observed change in cross-equatorial wind is a fingerprint of aerosol forcing. This zonal mean mode follows the evolution of global aerosol forcing that is distinct from the well-known regional changes in the Atlantic sector.