Oceanic Warming Has Lengthened Intense Tropical Cyclone Seasons Globally

Intense tropical cyclones (TCs), which pose significant threats to human life and property, often occur within a short period of time each year, known as the intense TC season. Changes in the lengths of intense TC seasons under climate change are critical scientific and socioeconomic issues. While recent research has investigated trends in overall TC seasons, the response of intense TC seasons to climate change remains underexplored. Here, we discover that intense TC seasons have been lengthening globally since 1980, with significant increasing trends ranging from 8.5–14.2 days/decade across all basins, equivalent to 6.5-21.2% increase in intense TC season lengths per decade. This is primarily driven by the enhancing thermodynamic disequilibrium between ocean and atmosphere due to recent oceanic warming, which raises the maximum potential intensity of TCs outside the traditional intense TC seasons. Meanwhile, changes in atmospheric circulation play a minor role. As a result, off-season TCs are more likely to develop into intense TCs. The findings in this study indicate an increasing exposure of human societies to intense TC risks outside historical seasonal norms. This suggests the urgent need for preparation and mitigation measures for the potential risks of intense TCs under future climate change.