Articles | Volume 16, issue 22
Research article
23 Nov 2016
Research article |  | 23 Nov 2016

Radiative effects of interannually varying vs. interannually invariant aerosol emissions from fires

Benjamin S. Grandey, Hsiang-He Lee, and Chien Wang

Abstract. Open-burning fires play an important role in the earth's climate system. In addition to contributing a substantial fraction of global emissions of carbon dioxide, they are a major source of atmospheric aerosols containing organic carbon, black carbon, and sulfate. These “fire aerosols” can influence the climate via direct and indirect radiative effects. In this study, we investigate these radiative effects and the hydrological fast response using the Community Atmosphere Model version 5 (CAM5). Emissions of fire aerosols exert a global mean net radiative effect of −1.0 W m−2, dominated by the cloud shortwave response to organic carbon aerosol. The net radiative effect is particularly strong over boreal regions. Conventionally, many climate modelling studies have used an interannually invariant monthly climatology of emissions of fire aerosols. However, by comparing simulations using interannually varying emissions vs. interannually invariant emissions, we find that ignoring the interannual variability of the emissions can lead to systematic overestimation of the strength of the net radiative effect of the fire aerosols. Globally, the overestimation is +23 % (−0.2 W m−2). Regionally, the overestimation can be substantially larger. For example, over Australia and New Zealand the overestimation is +58 % (−1.2 W m−2), while over Boreal Asia the overestimation is +43 % (−1.9 W m−2). The systematic overestimation of the net radiative effect of the fire aerosols is likely due to the non-linear influence of aerosols on clouds. However, ignoring interannual variability in the emissions does not appear to significantly impact the hydrological fast response. In order to improve understanding of the climate system, we need to take into account the interannual variability of aerosol emissions.

Short summary
Wildfires emit organic carbon aerosols, small particles suspended in the atmosphere. These aerosols may cool the climate system via interactions with sunlight and clouds. We have used a global climate model to investigate the cooling effects of these aerosols. We find that ignoring interannual variability of the emissions may lead to an overestimation of the cooling effect of the aerosols emitted by fires.
Final-revised paper