| Summary: | The recent decrease in Arctic sea ice extent is a significant indicator of ongoing climate change, with projections suggesting that summer Arctic sea ice could disappear in the near future. Furthermore, sudden sea ice loss events are projected to increase in frequency and magnitude, and these events could affect the climate to mid-latitudes through changes in the atmospheric circulation. However, an in-depth understanding of the atmospheric circulation response to Arctic sea ice loss remains elusive to date. In this framework, the general goal of this thesis is to improve the identification of the short-term climate impacts due to Arctic sea ice loss on the mid- and high latitudes of the Northern Hemisphere. To achieve this objective, a multi-model approach is employed, aiming to mitigate the potential biases in the use of a single model, thereby improving the reliability of the conclusions drawn. The first key finding of this thesis demonstrates that Arctic sea ice loss leads to an increase in the frequency and persistence of the surface air temperature and precipitation extremes across the peripheral Arctic regions, especially over islands such as Svalbard. The second key result underscores that the Barents-Kara sea ice extent anomalies exert a dominant influence on the winter atmospheric circulation, whereas other regional sea ice extent anomalies fail to yield consistent and robust atmospheric circulation changes. Notably, following a decrease in the Barents-Kara sea ice extent, a negative North Atlantic Oscillation (NAO)-like pattern emerged, consistent with the weakening of the stratospheric polar vortex. Lastly, this thesis provides valuable insights into the complexities of winter atmospheric circulation responses attributed solely to Arctic sea ice loss. Specifically, pan-Arctic sea ice loss leads to more robust atmospheric circulation responses, with a negative NAO-like pattern, than regional Arctic sea ice loss. This response to future pan-Arctic sea ice loss presents a divergence from the expected ...
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