North Atlantic freshwater events influence European weather in subsequent summers

• Main Authors: Oltmanns, Marilena, Holliday, N. Penny, Screen, James, Evans, D. Gwyn, Josey, Simon A., Bacon, Sheldon, Moat, Ben I.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; north atlantic current; North Atlantic
• Online Access: https://doi.org/10.5194/wcd-2021-79; https://wcd.copernicus.org/preprints/wcd-2021-79/

Amplified Arctic ice loss in recent decades has been linked to increased occurrence of extreme mid-latitude weather. The underlying dynamical mechanisms remain elusive, however. Here, we demonstrate a novel mechanism linking freshwater releases into the North Atlantic with summer weather in Europe. Combining remote sensing, atmospheric reanalyses and model simulations, we show that freshwater events in summer trigger progressively sharper sea surface temperature gradients in subsequent winters, destabilising the overlying atmosphere and inducing a northward shift in the North Atlantic Current. In turn, the jet stream over the North Atlantic is deflected northward in the following summers, leading to warmer and drier weather over Europe. Our results suggest that growing Arctic freshwater fluxes will increase the risk of heat waves and droughts over the coming decades, and could yield enhanced predictability of European summer weather, months to years in advance.