The Impact of Stratospheric Aerosol Injection on Extreme Fire Weather Risk

Stratospheric aerosol injection (SAI) would potentially be effective in limiting global warming and preserving large-scale temperature patterns; however, there are still gaps in understanding the impact of SAI on wildfire risk. In this study, extreme fire weather is assessed in an Earth system model experiment that deploys SAI beginning in 2035, targeting a global temperature increase of 1.5 degrees C above pre-industrial levels under a moderate warming scenario. After SAI deployment, increases in extreme fire weather event frequency from climate change are dampened over much of the globe, including the Mediterranean, northeast Brazil, and eastern Europe. However, SAI has little impact over the western Amazon and northern Australia and causes larger increases in extreme fire weather frequency in west central Africa relative to the moderate emissions scenario. Variations in the impacts of warming and SAI on moisture conditions on different time scales determine the spatiotemporal differences in extreme fire weather frequency changes, and are plausibly linked to changes in synoptic-scale circulation. This study highlights that regional and spatial heterogeneities of SAI climate effects simulated in a model are amplified when assessing wildfire risk, and that these differences must be accounted for when quantifying the possible benefit of SAI. Plain Language Summary Under human-caused climate change, wildfire risk is expected to increase in many parts of the globe as temperatures increase and precipitation, humidity, and wind patterns shift. This study investigates how one form of solar climate intervention-injecting sunlight-reflecting aerosols high into the atmosphere, or Stratospheric Aerosol Injection (SAI)-could slow down this trend. The resulting global cooling, when SAI is simulated in a climate model, limits the increases in meteorological conditions that can lead to wildfire spread. However, in some locations there are reductions in precipitation and humidity and increases in wind speed, which leads to regional increases in wildfire risk under SAI. This study highlights both the benefit and unintended consequences of SAI on global wildfire risk and the need to continue understanding the role of climate intervention in limiting increases in extreme climate events.