Extreme cold winters and hot summers over Eurasia are intensifying under global warming, posing substantial risks to agriculture, ecosystems, and human health. Here, we show that a colder winter tends to be followed by a hotter summer over Eurasia. This winter-summer extreme temperature reversal is linked to the phase switch of the Arctic oscillation (AO) from winter to summer, which is driven by the North Atlantic air–sea interaction and Arctic sea ice-atmosphere coupling. Specifically, a negative AO in winter weakens high-latitude westerlies, causing cold extremes over Eurasia. Negative AO also induces a tripolar sea surface temperature anomaly in the North Atlantic that persists into the following summer and triggers positive AO-like atmospheric anomalies, leading to a hotter summer across Eurasia. Moreover, winter atmospheric anomalies reduce the Barents–Kara sea ice through horizontal moisture transport. This sea ice loss persists into summer and contributes to the formation of positive AO-like atmospheric anomalies. These processes establish a cross-seasonal transition from extreme cold winters to extreme hot summers over Eurasia, offering new insight into the prediction of summer extreme events.

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