Increasing central and northern European summer heatwave intensity due to forced internal variability changes

In recent years European summer heatwaves have strongly intensified due to rising anthropogenic emissions. While European summer heatwaves will continue to intensify due to the warming of summer temperatures, the effects of the changes in internal variability under global warming remain unknown. Employing four single-model initial condition large ensembles, we find that the forced internal variability change is projected to intensify central and northern European summer heatwaves. Central and northern Europe will experience frequent moisture limitations, enhancing land-atmospheric feedback and increasing heatwave intensity and variability. In contrast, the forced internal variability change will contribute to weaken southern European summer heatwaves. Southern Europe is projected to face a more stable moisture-depleted environment that reduces extreme temperature variability and heatwave intensity. Our findings imply that while adaptation to increasing mean temperatures in southern Europe should suffice to reduce the vulnerability to increasing heatwave intensity, in central and northern Europe adaptation to increased temperature variability will also be needed.