New Study Analyzes Extreme Heat by the Hour, Revealing Accelerated Increase

Hourly Analysis of Extreme Heat

A new study led by Weilin Liao and Xuanzong Zhang at Sun Yat-sen University has introduced an hourly approach to analyzing extreme heat. Unlike traditional methods that use daily minimum, maximum, or mean temperatures, this research examines temperatures for each hour of the day separately. Extreme heat is defined as temperatures above the 90th percentile for that specific hour between 1981 and 2010.

Observed Trends in Hourly Extremes

The study found that the global average experience of "hourly heat extremes" is approximately 270 hours each summer. This number has been increasing by 62 hours per decade. This hourly breakdown provides a more granular view of how frequently and intensely extreme heat is occurring.

Future Projections

Using climate model results from two future greenhouse gas emission scenarios, the researchers projected future increases. In a medium emissions scenario, leading to 3°C warming by 2100, the total number of hourly heat extremes is projected to triple by 2070–2099 compared to the past couple of decades. Under a high emissions scenario, with 5°C warming, the increase is 4.5 times. The study indicates that for every half-degree Celsius of global average temperature increase, there will be an additional 200 hot hours per summer.