Hot days could gain more than four extra hours of extreme heat by the year 2100 under the most extreme emissions scenario, according to a new study from Sun Yat-sen University in Guangzhou, China.
The warning comes as the UK braces for its fifth heatwave of the summer, with temperatures expected to reach as high as 37°C in parts of the country. The researchers say this could be a mere taste of what is to come.
The team modelled various emissions scenarios and found that in the most extreme case, hot days could gain more than four extra hours of extreme heat by 2100. Worryingly, these extra hours are expected to occur at night, a time when people usually get some relief from extreme heat.
The scientists wrote in their study, published in Nature Climate Change, that the health implications of hourly heat extremes are profound. They said nighttime has traditionally been regarded as a relief from daytime heat, but that this is not the case under abnormally warm nights, since uninterrupted heat exposure through the night undermines that cooling window and increases the risk of heat-related illness and death, especially among vulnerable populations.
Measuring heat by the hour
Extreme heat events are usually assessed using daily average, maximum or minimum temperatures. While this approach is valuable, the researchers instead focused on shorter periods of extreme heat measured in hours.
The team studied global hourly data from 1981 to 2023 and found that land areas experience an average of 269 hours of extreme heat each summer. They then used climate projections to predict how that figure might change under a high-emissions scenario.
Their projections suggest that by the period 2070 to 2099, each hot day could contain more than four additional hot hours compared with present-day levels.
Unequal impact and calls for more research
Heat exposure is not shared equally around the world, according to the researchers. They said low- and middle-income countries bear the brunt of both current and future hourly heat exposure, despite having contributed less to historical emissions.
Based on the findings, the team called for further research into the mechanisms that cause hourly heat extremes, such as heat bursts or flash heat events. They said improved understanding of short-term heat events on an hourly scale could improve early warning systems, health risk assessments, and adaptation to a warming climate.
Record heat across Western Europe
The study follows data confirming that Western Europe just experienced its hottest June-July period on record, with average temperatures reaching 21.62°C (70.9°F). That figure is 2.79°C (5°F) above the monthly average, breaking the previous record set in 2022, as the continent endures its fourth successive heatwave.
