For weeks, people in South Asia have been suffering from a severe heat wave, with some days the air temperature reaching 50 degrees Celsius in the region. Even at night it hardly cools down, which affects health and is likely to lead to many deaths. The heat wave in India and Pakistan is part of a series of such extreme weather events: in the summer of 2021, the northwestern United States and western Canada were glowing red, and at the start of 2022, the thermometer in Argentina has reached record values. A study by Vikki Thompson of the University of Bristol and her team in “Science Advances” has identified some of the most extreme heat waves of recent decades, some of which have received little media attention..

For example, the temperature in Lytton, Canada reached 49.6 degrees Celsius on June 29, 2021, breaking the region’s previous record of 4.6 degrees Celsius. The highest daily average was still 39.5 degrees Celsius. However, this event was overshadowed by various heat waves, during which the standard deviation from the mean temperatures of the respective seasons was even higher than in Canada. In Southeast Asia in April 1998 with 32.8 degrees Celsius, in Brazil in November 1985 with 36.5 degrees Celsius and in the southern USA in July 1980 with 38.4 degrees Celsius (each maximum temperature), the values were sometimes more than five units above previous peaks in these regions: significant jumps, even if the maximum temperatures remained lower than those of Canada or currently of South Asia.

“The heat wave in western North America will be remembered for its extreme consequences. However, our study reveals several major weather extremes over the past few decades, some of which have remained largely under the radar, likely because they occurred in poorer countries. It is important to assess the severity of heat waves based on local temperature variations as humans and natural ecosystems adapt to them. So in regions with less variability, even a smaller absolute maximum can have a bigger impact,” says Thompson.