European summer weather linked to North Atlantic freshwater events in preceding years

• Main Authors: Oltmanns, Marilena, Holliday, N. Penny, Screen, James, Moat, Ben I., Josey, Simon A., Evans, D. Gwyn, Bacon, Sheldon
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; north atlantic current; North Atlantic; Sea ice
• Online Access: https://doi.org/10.5194/wcd-2023-1; https://wcd.copernicus.org/preprints/wcd-2023-1/

Amplified Arctic ice loss in recent decades has been linked to increased occurrence of extreme mid-latitude weather. The underlying mechanisms remain elusive, however. One potential link occurs through the ocean as the loss of sea ice and glacial ice leads to increased freshwater fluxes into the North Atlantic. Thus, in this study, we examine the extent to which North Atlantic freshwater anomalies constrain the subsequent ocean-atmosphere evolution and assess their implications for European summer weather. Combining remote sensing, atmospheric reanalyses and model simulations, we show that stronger freshwater anomalies are associated with sharper sea surface temperature gradients over the North Atlantic in winter, 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 freshwater fluxes into the North Atlantic 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.