More extreme summertime North Atlantic Oscillation under climate change

Extreme states of the North Atlantic Oscillation in summer can lead to severe weather events such as heatwaves and floods in Europe. But how these extremes evolve in response to climate change remains unexplored. Here we show that the statistical distribution of the summer North Atlantic Oscillation index grows wider with increasing global warming in large ensembles of climate change simulations as well as reanalysis data. Such an amplified variability of the summer North Atlantic Oscillation caused by global warming leads to a higher probability of summer North Atlantic Oscillation extremes — for both positive and negative phases — accompanied by an amplification of their impacts on surface temperature over northwestern Europe. Changes in summer North Atlantic Oscillation extremes highlight the effects of climate change on the transient behaviour of the atmosphere, and thus have important implications for extreme weather attribution.