Publication Date:
2016-01-06
Description:
Aridity Index (AI), defined as the ratio of precipitation to potential evapotranspiration (PET), is a measure of the dryness of terrestrial climate. Global climate models generally project future decreases of AI (drying) associated with global warming scenarios driven by increasing greenhouse gas and declining aerosols. Given their different effects in the climate system, scattering and absorbing aerosols may affect AI differently. Here we explore the terrestrial aridity responses to anthropogenic black carbon (BC) and sulfate (SO 4 ) aerosols with Community Earth System Model (CESM) simulations. Positive BC radiative forcing decreases precipitation averaged over global land at a rate of 0.9% per °C of global mean surface temperature (SAT) increase (moderate drying) while BC radiative forcing increases PET by 1.0%/°C (also drying). BC leads to a global decrease of 1.9%/°C in AI (drying). SO 4 forcing is negative, and causes precipitation a decrease at a rate of 6.7% per °C cooling (strong drying). PET also decreases in response to SO 4 aerosol cooling by 6.3% per °C cooling (contributing to moistening). Thus SO 4 cooling leads to a small decrease in AI (drying) by 0.4% per °C cooling. Despite the opposite effects on global mean temperature, BC and SO 4 both contribute to the 20th century drying (AI decrease). Sensitivity test indicate that surface temperature and surface available energy changes dominate BC and SO 4 -induced PET change.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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