Impact of global warming and anomalously high sea surface temperatures around Japan during a week-long heavy snowfall in February 2025

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Under ongoing global warming, record-breaking heavy snowfall occurred in Japan in February 2025. During that winter, the sea surface temperatures (SSTs) around Japan were markedly higher than the climatological mean. This study investigates the impacts of global warming and anomalously high SSTs on heavy snowfall in Japan in February 2025 using the pseudo global warming method and SST sensitivity experiments. Precipitation increases by 7.8%, while snowfall decreases by 2.0%, owing to past global warming over land areas below 100 m along the Sea of Japan coast. Further global warming, assuming 2 K and 4 K warmer conditions relative to the pre-industrial period, intensifies precipitation, whereas snowfall decreases by 9.3% and by a substantial 42.6%, respectively. In contrast, the high SST anomalies enhance precipitation and snowfall by 21.8% and 17.5%, respectively, over land areas below 100 m. The anomalously high SSTs not only increase atmospheric moisture but also enhance atmospheric instability, resulting in a marked increase in precipitation and snowfall. By comparison, global warming induces a slight atmospheric stabilization, which suppresses the precipitation increase expected under enhanced moisture and warming. The southeastern part of Japan’s northern island, where record-breaking heavy snowfall occurred on February 3, 2025, also shows increased snowfall attributable to global warming and a high SST anomaly. In this region, the high SST anomaly strengthens the horizontal thermal contrast between land and the ocean, thereby enhancing the ascent of moist air along the boundary between inland areas and the ocean and resulting in further enhanced precipitation.