News release

From: Springer Nature

Global hourly extreme heat events increasing

Hot days could gain more than four additional hours of extreme heat by the end of the century under a high-emissions scenario, according to a modelling study published in Nature Climate Change. The findings show that hourly assessments can capture heat exposure overlooked by daily metrics and could support more effective heat risk management and public health planning.

Extreme heat events are typically assessed using daily mean average, maximum, or minimum temperatures. However, these measures can neglect shorter but potentially important periods of extreme heat.

Xiaoping Liu and colleagues studied global hourly data, which combine weather observations and model estimates, from 1981 to 2023, coupled with future climate projections to the end of the twenty-first century. In that timeframe, they estimate that global land areas experience an average of approximately 269 hours of extreme heat each summer. The authors define an hourly heat event as temperature exceeding the 90th percentile compared with that hour during the baseline of 1981–2010. More than 80% of global land showed an increase in heat, with an average of 62 additional hours per decade of extreme heat between 1981 and 2023. 28% of these events were also found to occur on days not identified as heat extremes by daily metrics.

Under a high-emissions scenario (SSP5-8.5), the authors project that by 2070–2099 each hot day could contain more than four additional hot hours compared with present-day levels (2001–2023). They also project that non-hot days could gain a further three hot hours that are likely to remain undetected by daily measures. Low- and middle-income countries account for more than three-quarters of both current and projected heat exposure and face the largest increases in lifetime exposure across generations.

Future research should focus on the mechanisms that cause hourly heat extremes, such as heat bursts or flash heat events. Improved understanding of short-term heat events on an hourly scale could improve early warning systems, potential health risk assessments, and adaptation to a warming climate, the authors argue.