An unusual heat wave has been plaguing people in India and Pakistan for weeks. Much is reported about it – according to the researchers, however, some equally severe heat waves of the past decades have gone largely unnoticed. The likely reason is that the extremes occurred in poorer countries or regions with less data available, they write in the journal Science Advances.

Temperature deviations from the average are significant

“It is important to assess the severity of heat waves based on local temperature variability because humans and the natural ecosystem adapt to it, so in regions with less variability, a smaller absolute extreme may have a greater impact,” said climatologist Vikki Thompson. . His team at the University of Bristol analyzed heat waves from 1950 to 2021.

In each case, deviations from average daily maximum temperature fluctuations over the past decade were calculated. The heat wave in western North America in the summer of 2021 set a record: on June 29, a Canadian maximum of 49.6 degrees was measured in the town of Lytton, British Columbia. The previous record since 1950 was exceeded by 4.6 degrees. With hundreds of victims, the heat wave was the deadliest weather event in Canada to date. The forest fires are said to have caused extensive damage to infrastructure and crop failures.

According to the analysis, the three most severe heat waves in the world – compared to typical departures for the respective time of year – occurred in Southeast Asia in April 1998, in Brazil in November 1985 and in the southern United States in July 1980. 2003 heat wave, on the other hand, counts according to the chosen calculation method, and not according to peak events.

The intensity of heat waves is expected to continue to increase

In general, scientists emphasize that this is not a definitive list of the most extreme events. Even small changes in methodology, such as temporal resolution or regional assignments, could alter the events identified or their order.

Using climate model projections, scientists drew conclusions about developments over the century. The analysis therefore confirms predictions that the intensity of heat waves will increase as global temperatures rise. Thompson’s team warns that regions that have not experienced a recent extreme heat wave may be less prepared for potential events to come. This applies, for example, to parts of Australia and Central Africa.

It must also be taken into account that the effects of heat in cities are amplified. Given that almost 70% of the world’s population is projected to live in cities by 2050, the risks of extreme heat events would also increase there.