Europe-Atlantic jet caused dipole mode of European climate and increased climatic extremes

The jet stream configuration over the Atlantic Ocean and the European continent substantially affects climatic extremes in Western Eurasia by transporting heat and vorticity. However, how the Europe-Atlantic jet configuration varies and how it affects European climate on the long time-scales are still unclear. We compiled a network of tree-ring width, blue intensity, and maximum density chronologies from Europe to explore past variability in the summer Europe-Atlantic Jet stream and its influence on regional climate. By combining five regional chronologies, we were able to reconstruct July-August jet stream latitude (JSL) PC2 variability over the past millennium (978-2010 CE) for the Europe-Atlantic domain (30°W to 40°E). Our reconstruction explains 40% of summer JSL PC2 variability over the instrumental period (1948-2010 CE) with strong skill. Our millennial-long reconstruction shows that summer JSL is a relevant driver of the temperature, precipitation, and drought dipoles observed between Northwestern and Southern Europe. Positive summer JSL PC2 values (northward jet position) generally lead to a strengthening of the European summer climate dipole, while negative values (southward jet position) lead to a weak or insignificant dipole mode. Our summer JSL reconstruction shows large variability and a high occurrence rate of extremes over the 20^th century, as well as 1200-1350 CE Medieval Climate Anomaly (MCA). The high occurrence rate of summer JSL extremes corresponds to periods with increased number of climatic extremes. Our results suggest that the summer JSL contributes to the European climate dipole both in a long-term context and in its extremes. We also reveal that the occurrence rate of summer JSL extremes is double during the 20^th century compared to other periods, especially for the negative extremes, which might be related to anthropogenic warming. Our results suggest a high occurrence rate of summer JSL extremes during the 20^th century, leading to more climatic extremes in Europe, as well as a prevailing northward summer JSL position resulting in a weakening climatic dipole.