PNNL

Abstract

Aerosols emitted from wildfires could significantly affect global climate 31 through perturbing global radiation balance. In this study, Community Earth System 32 Model with prescribed daily fire aerosol emissions is used to investigate fire 33 aerosols’ impacts on global climate with emphasizing the role of climate feedbacks. 34 The total global fire aerosol radiative effect (RE) is estimated to be -0.78±0.29 W 35 m-2, which is mostly from shortwave RE due to aerosol-cloud interactions (REaci, 36 -0.70±0.20 W m-2). The associated global-annual mean surface air temperature 37 (SAT) change (?T) is -0.64±0.16K with the largest reduction in the Arctic regions 38 where the shortwave REaci is strong. Associated with the cooling, the Arctic sea ice 39 is increased, which acts to re-amplify the Arctic cooling through a positive 40 ice-albedo feedback. The fast response (irrelevant to ?T) tends to decrease surface 41 latent heat flux into atmosphere in the tropics to balance strong atmospheric fire 42 black carbon absorption, which reduces the precipitation in the tropical land regions 43 (southern Africa and South America). The climate feedback processes (associated 44 with ?T) lead to a significant surface latent heat flux reduction over global ocean 45 areas, which could explain most (~80%) of the global precipitation reduction. The 46 precipitation significantly decreases in deep tropical regions (5°N), but increases in 47 Southern Hemisphere tropical ocean, which is associated with the southward shift 48 of the Inter-Tropical Convergence Zone and the weakening of Southern Hemisphere 49 Hadley cell. Such changes could partly compensate the interhemispheric 50 temperature asymmetry induced by boreal-forest fire aerosol indirect effect, through 51 intensifying the cross-equator atmospheric heat transport.