Large-scale impacts of the 2023 Canadian wildfires on the Northern Hemisphere atmosphere

Abstract Climate change projections are expected to increase wildfire activity in many world regions in the coming decades because of rising mean temperatures and hydrological changes. This increase is especially pronounced in the high latitudes, and the large-scale weather impact of the resulting increased emissions has not been comprehensively explored so far. In this study, we investigate the impacts of the extreme Canadian wildfires of 2023 with a state-of-the-art Earth system model, comparing modelled atmospheric conditions with and without wildfire emissions. We find significant increases in aerosol abundances throughout much of the Northern Hemisphere (NH), with wildfire aerosols leading to a hemispheric surface air temperature decrease. This modelled cooling takes place because of direct aerosol-radiation interactions, amplified by cloud cover and circulation modifications. Influences of aerosols on meteorology are pronounced even in parts of the NH where smoke transport is minimal. Our results highlight the importance of modelling wildfire-generated aerosols, as extreme fires can lead to local and remote long-lasting hemispheric temperature anomalies.