Warming climate has lengthened global intense tropical cyclone seasons

Intense tropical cyclones (TCs), which pose serious 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 trends in overall TC seasons have been widely studied, the response of intense TC seasons to climate change remains underexplored. Here, we show that intense TC seasons have been lengthening globally since 1980, with statistically significant increasing trends ranging from 9.9-13.8 days/decade across all basins, equivalent to 7.4-21.9% increase in intense TC season lengths per decade. This is primarily due to the enhancing probability of off-season TCs experiencing rapid intensification, which is partly driven by oceanic warming. Meanwhile, changes in background atmospheric circulation play a role in the complexity of intense TC seasonality change. 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.