Study projects four extra hours of extreme heat per hot day by 2100
This digest was compiled by AI from multiple sources — links to the originals are below.
A modeling study published in Nature Climate Change projects that under a high-emissions scenario, hot days could gain more than four additional hours of extreme heat by 2070–2099. Low- and middle-income countries would bear over three-quarters of the increased heat exposure. Non-hot days are also projected to gain hot hours that daily temperature metrics fail to detect.
The Hourly Scale
Researchers from Sun Yat-sen University analyzed global hourly temperature data from 1981 to 2023, combined with climate projections. They found that global land areas already average 269 hours of extreme heat each summer, defined as hours exceeding the 90th percentile of the 1981–2010 baseline. More than 80% of land showed an increase, with an average of 62 additional extreme-heat hours per decade. Crucially, 28% of these events occurred on days not classified as heat extremes by daily metrics. The study projects that by 2070–2099, each hot day could contain over four extra hot hours compared to 2001–2023 levels.
Unequal Exposure
Low- and middle-income countries account for over 75% of both current and projected heat exposure and face the largest intergenerational increases. Under the high-emissions SSP5-8.5 pathway, these regions will see the sharpest rise in lifetime exposure to hourly heat extremes. The authors note that short-duration heat bursts, often missed by daily assessments, disproportionately affect vulnerable populations. Non-hot days could gain three additional undetected hot hours, compounding risks for communities without adequate cooling infrastructure.
What's Next
The researchers call for future work on the mechanisms behind hourly heat extremes, such as flash heat events, to strengthen early warning systems. Whether global emission cuts can steer the trajectory away from the high-emissions scenario remains uncertain.
2 sources
Study projects four extra hours of extreme heat per hot day by 2100
