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The past, present and future of African dust

This decline in dust over North Africa may result in a slight improvement in air quality in the region, although the effect of regional population growth and urbanization will undoubtedly overshadow the benefits of a reduction in airborne dust. While the radiative forcing of dust may be near zero over North Africa, as shortwave cooling is approximately balanced by the longwave warming, dust transported over the tropical North Atlantic cools the surface via direct and indirect radiative effects. Therefore, a reduction in dust would act as a positive feedback to warming by greenhouse gases in the tropical North Atlantic. Furthermore, since this feedback is not pan-tropical, this additional dust-forced warming could increase hurricane activity by increasing tropical North Atlantic sea surface temperature, relative sea surface temperature (which is the difference between sea surface temperature in the tropical Atlantic and the sea surface temperature averaged over all of the tropics), and the northward meridional sea surface temperature gradient. The radiative and temperature effects from such a reduction in dust are not captured in most CMIP5 simulations; many models do not have interactive dust, and of those models that do, the majority show an increase in simulated African dust concentrations during the twenty-first century. Thus, it is plausible that current temperature projections for the tropical Atlantic through the Caribbean are too conservative.

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