The impact of wildfire aerosols on near surface climate and gross primary production in the E3SM Earth System Model

Tuesday, December 10, 2019 - 08:00
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Fire-emitted trace gases and aerosols play important roles in influencing the Earth’s climate system. Fire aerosols directly scatter and absorb incoming solar radiation and indirectly alter cloud microphysical properties. Together, aerosol direct and indirect effects influence surface temperature, precipitation and light environment, which consequently affect global patterns of gross primary production (GPP). Here we optimized fire-associated trace gases and aerosol emissions in the Energy Exascale Earth System Model (E3SM) using the Global Fire Emissions Database version 4s (GFED4s) and AERONET aerosol optical depth (AOD) observations. We distributed fire emissions from the surface through the upper troposphere using smoke plume heights derived from the MISR satellite. With the optimized emissions, we performed two 20-year simulations (with and without fires) during 1997-2016 to assess contemporary fire aerosol effects on near surface climate and GPP. We found that fire aerosols considerably increased AOD in the tropics (30°S to 30°N) by 0.03 (15%). At a global scale, the combination of absorbing and scattering aerosols emitted by fires caused a small positive net shortwave forcing at the top of the atmosphere (0.27±0.07 W m-2) but a reduction in net shortwave radiation at the surface (-1.43±0.39 W m-2). Fire aerosols contributed to a negative indirect aerosol effect through their effects on cloud droplet number and cloud albedo. Together, direct and indirect aerosol effects from fires caused global surface air temperatures over land to decrease by -0.11±0.20°C. Fire-induced changes in surface air temperatures, diffuse and direct solar radiation, and precipitation caused complex regional GPP changes, with large increases occurring in southern Africa (5.9±6.5%) and decreases in other regions. Our analysis highlights the importance of wildfire as a driver of global ecological teleconnections.

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