In 1981, climate researchers began tracking hourly temperatures that would eventually span 43 years of global data. 47 years later, their projections show hot days could contain more than 4 extra hours of extreme heat, revealing risks daily averages miss

When scientists study extreme heat, they often rely on daily minimum, maximum or average temperatures. Heatwaves are also commonly measured by how many days temperatures remain above a certain threshold. But looking at heat one day at a time can hide what happens during individual hours.

A new study led by Weilin Liao and Xuanzong Zhang at Sun Yat-sen University examined global heat extremes hour by hour. Using temperature records from 1981 to 2010 to establish hourly thresholds, the researchers found that extreme heat is becoming more frequent and that hot hours are increasing faster than hot days, as per an Ars Technica report.