Aerosol-induced thermal effects increase modelled terrestrial photosynthesis and transpiration

Abstract

Previous studies suggest that the radiative effects of atmospheric aerosols (reducing total radiation while increasing thediffuse fraction) can enhance terrestrial productivity. Here, simulations using a regional climate/terrestrial biospheremodel suggest that atmospheric aerosols could also enhance terrestrial photosynthesis and transpiration through aninteraction between solar radiation, leaf temperature and stomatal conductance. During midday, clear-sky conditions, sunlit-leaf temperatures can exceed the optimum for photosynthesis, depressing both photosynthesis and transpiration.Aerosols decrease surface solar radiation, thereby reducing leaf temperatures and enhancing sunlit-leaf photosynthesisand transpiration. This modelling study finds that, under certain conditions, this thermal response of aerosols can havea greater impact on photosynthesis and transpiration than the radiative response. This implies that a full understandingof the impact of aerosols on climate and the global carbon cycle requires consideration of the biophysical responses ofterrestrial vegetation as well as atmospheric radiative and thermodynamic effects.