Ultra flash cold events under global warming

It is widely assumed that global warming will make winters milder and reduce extreme cold. However, this assumption is contradicted by the recurrence of flash cold (FC) events-sudden, violent temperature drops that can freeze energy grids and infrastructure within hours. The 2021 North America freeze, which caused over $20 billion in losses, stands as a stark warning. Here, we find that while the world warms, the fate of these ultra FC events is diverging: they are fading over Eurasia but significantly intensifying over North America. By tracking the spatiotemporal evolution of these ultra FC events and characterizing their dynamic environment, we reveal that this contrast is driven by specific atmospheric circulation regimes. In North America, increasingly frequent Alaska-Arctic anticyclonic anomalies funnel cold air directly southward. Conversely, weakened Ural-Arctic cyclonic anomalies are cutting off the cold supply. Crucially, current climate models fail to reproduce this intercontinental divergence. Simulations largely miss these specific circulation regimes, leading models to underestimate the ultra FC risk. Our results expose a regional warming paradox: specific atmospheric circulation anomalies can transiently overwhelm background warming, creating a critical blind spot for energy security.