Extreme cold winters and hot summers over Eurasia are intensifying under global warming, pos
ing 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 tem
perature reversal is linked to the phase switch of the Arctic oscillation (AO) from winter to sum
mer, which is driven by the North Atlantic air–sea interaction and Arctic sea ice-atmosphere coup
ling. 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 anom
alies, 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 pro
cesses 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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