An observation-based causal framework linking Barents–Kara sea ice to European heatwaves

Abstract European summers have become increasingly dominated by severe and persistent heatwaves (HWs), with major societal and economic consequences. While progress has been made in the last decade in linking Arctic sea ice decline to midlatitude extremes, the causal nature of this connection remains debated. Here, we develop a novel observation-based framework that integrates empirical orthogonal function and composite analyses with Granger causality and convergent cross mapping methods, allowing us to assess both linear and nonlinear causal pathways. Using high-resolution observations for 1950–2024, we demonstrate that declining Barents–Kara seas (BKS) sea ice is causally linked to increases in the number, duration, and frequency of European HWs. We find the strongest and most consistent signals over Eastern Europe, including Ukraine and Moldova, countries that rank among the poorest in Europe and where populations are further affected by recent conflict-related traumas. BKS sea ice loss weakens the jet stream, promoting persistent high-pressure systems and reducing cloud cover, thereby creating conditions conducive to long-lasting HWs over these regions. As BKS sea ice loss will likely continue in the coming decades under anthropogenic warming, our findings emphasize the urgent need for targeted adaptation and risk management strategies, particularly over Europe’s most vulnerable regions.