The impact of Arctic sea‐ice loss on winter weather in the British Isles

Abstract We use simulations from the Polar Amplification Model Intercomparison Project to understand the impact of Arctic sea‐ice loss in isolation, as well as within the context of general greenhouse warming, on projections of wintertime weather for the British Isles. At large scales, sea‐ice loss results in a more negative North Atlantic Oscillation across all participating models, as well as more positive East Atlantic and Scandinavian Patterns, alongside an equatorward shift in the North Atlantic eddy‐driven jet. Strong extratropical cyclones become weaker and less frequent and they propagate more slowly. At the regional scale of the British Isles, there is often little inter‐model agreement in the responses of mean and extreme precipitation, surface winds, and temperature, but the spread is generally correlated with model spread in larger‐scale circulation and storminess. Whether the effect of sea‐ice loss can be expected to be a dominant contributor to projections of weather in the region is examined by comparison with experiments that isolate ocean surface warming, as well as by considering the range of plausible storylines of sea‐ice loss and warming. Simulated dynamical changes due to ocean warming are often of the opposite sign to those due to sea‐ice loss, creating a tug‐of‐war on the weather of the region. While ocean warming is the dominant driver of projected thermodynamical changes over the British Isles, projected dynamical changes depend strongly on the relative magnitudes of future sea‐ice loss and ocean warming.