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Cyclones play an important role in the coupled dynamics of the Arctic climate system on a range of time scales. Modeling studies suggest that storminess will increase in Arctic summer due to enhanced land-sea thermal contrast along the Arctic coastline, in a region known as the Arctic Frontal Zone (AFZ). However, the climate models used in these studies are poor at reproducing the present-day Arctic summer cyclone climatology and so their projections of Arctic cyclones and related quantities, such as sea ice, may not be reliable. In this study we perform composite analysis of Arctic cyclone statistics using AFZ variability as an analog for climate change. High AFZ years are characterized both by increased cyclone frequency and dynamical intensity, compared to low years. Importantly, the size of the response in this analog suggests that General Circulation Models may underestimate the response of Arctic cyclones to climate change, given a similar change in baroclinicity.

Plain Language Summary The dramatic reduction in Arctic summer sea ice has led to an increase in human activity and hence exposure to extreme events in the Arctic. Unlike the midlatitude storm tracks, which are most active in winter, the Arctic storm track is most active in summer, exactly during the time when shipping and tourism are on the rise, leading to the obvious question of how climate change is affecting and will affect the storms themselves. Unfortunately, according to previous research by ourselves and others, climate models perform poorly in representing even the basic features, such as the summer maximum in Arctic cyclone frequency. As a result their projections for how Arctic cyclones will change in the future cannot be considered reliable. In this paper we use a new analog approach to assess the impact of a warming Arctic, using the observed record. By comparing statistics for years with high land-sea thermal contrast against years with low, we demonstrate that storms over the Arctic Ocean will likely become more frequent and more dynamically intense as the climate warms, increasing the risk to shipping and other human activities.