Reduced Anthropogenic Aerosols Reveal Increased Heatwaves Driven by Climate Warming

Understanding the contributions of anthropogenic climate forcings to heatwave intensification is essential for evaluating mitigation strategies. While greenhouse gas influences on temperature extremes are well established, the impacts of other anthropogenic forcings, particularly aerosols, remain inadequately characterized. Here, we quantify the distinct contributions of greenhouse gases, anthropogenic aerosols, and natural forcings to extreme heatwave metrics from the pre-industrial period. Globally, changes in the duration of heatwave events and cumulative heat are +2.77 ± 0.85 days and +1.76 ± 0.31°C² attributed to greenhouse gases, and −1.10 ± 0.34 days and −0.85 ± 0.14°C² due to anthropogenic aerosols, respectively, over the past 3 decades relative to pre-industrial levels. This indicates that aerosols substantially masked greenhouse gas effects until the 1990s. Under current mitigation policies, declining aerosol emissions have exacerbated heatwave intensification at rates of +1.07 ± 0.32 days decade⁻¹ and +0.47 ± 0.09°C² decade⁻¹ for duration and cumulative heat respectively, exceeding the intensification attributable to greenhouse gases alone. Heatwave intensification has been driven primarily by reduced cloud cover and increased shortwave radiation resulting from weakening aerosol forcing, especially in Central North America and Europe. However, the regional climate changes driven by greenhouse gases and aerosols exhibit spatial heterogeneity, highlighting the necessity for geographically targeted mitigation strategies.