Abstract
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.
Highlights
There are many types of open-burning fires, caused by both natural and human influences
The conventional global mean net radiative flux perturbations (RFPs) associated with fire aerosols is −1.3 W m−2 (Table 1)
Note that this RFP is relative to simulation F0 which has zero emissions of fire aerosols
Summary
There are many types of open-burning fires, caused by both natural and human influences. Broad categories include agricultural waste burning, grassland fire, peat fire, and various types of forest fire (van der Werf et al, 2010). In addition to producing heat, these fires emit pollutants into the atmosphere. One such pollutant is carbon dioxide, contributing to climate change – Page et al (2002) estimate that the largescale burning of peat and forests in 1997 in Indonesia alone emitted the equivalent of 13–40 % of global annual emissions of carbon dioxide from fossil fuels. Other pollutants include aerosols, containing organic carbon, black carbon, and sulfate. These aerosols have a negative impact on air quality and human health (Lelieveld et al, 2015)
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