The impact of anthropogenic aerosols on the large-scale atmosphere and ocean circulation patterns

Abstract

This research describes the role that human emitted aerosols play in influencing the circulation patterns of the ocean and atmosphere on a global and regional scale. Utilising targeted experiments from global climate models, it is shown that aerosols induce a substantial cooling over the Northern Hemisphere. This has a wide ranging impact, from suppressing the Asian summer monsoon to mitigating the slowdown of the global meridional overturning circulation due to greenhouse warming. Simulations over the late twentieth century that isolate the impacts of anthropogenic aerosols, also suggest that these pollutants have enhanced the cooling of the sub-surface tropical and subtropical oceans of the Southern Hemisphere. Aerosols are also implicated in altering the mean climatological conditions across the tropical Indian Ocean, contributing to the enhanced asymmetry between the phases of the Indian Ocean dipole. Coupled ocean-atmosphere modelling experiments show that the increase in Asian anthropogenic aerosol emissions in the late twentieth century played a very minor role in the aforementioned circulation trends, particularly the weakening of the Asian monsoon and strengthening of the global meridional overturning circulation. The enhanced climatic response to aerosols in the atmosphere and ocean circulation predominantly resulted from historical emissions from Europe, the Former Soviet Union and North America in the mid-twentieth century. The research highlights the many uncertainties that are associated with anthropogenic aerosols and their potential impacts in coupled ocean-atmosphere models. This has far-reaching implications given that, globally, human-generated aerosols are projected to further decline in the twenty-first century, potentially unmasking the wide-reaching impact of greenhouse-induced warming on the climate.