Climate data analyzed since 1950
Where there have been the most extreme heat waves
In some parts of the world, ecosystems and humans have become accustomed to high temperatures. Even small upward fluctuations can then have serious effects. Given this relative intensity, many heat waves of the past 70 years have gone unnoticed.
An unusual heat wave has been plaguing people in India and Pakistan for weeks. Much is reported about this – 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 available data, they write in the journal Science Advances.
The team led by climatologist Vikki Thompson from the University of Bristol took relative intensity into account for the assessment, i.e. how extreme a heat wave was compared to temperature fluctuations normal locales. “It’s important to assess the severity of heat waves based on local temperature variations,” Thompson said. The scientist justifies this by saying that “humans and the natural ecosystem adapt to it, so that in regions with smaller fluctuations, a smaller absolute extreme can have larger effects”. The period from 1950 to 2021 has been included.
4.6 degrees above maximum measured
In each case, the deviation from the average daily maximum temperature fluctuations in the respective region over the past decade was calculated. The heat wave in western North America last summer set a record: on June 29, a Canadian high 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, and the associated wildfires caused extensive infrastructure damage and crop failures.
Five other heat waves around the world since 1960 have been even more extreme in their relative intensity – some barely reported. 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. The European heat wave of 2003, on the other hand, counts according to the chosen calculation method, for example, not for peak events.
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.
Climate change “the biggest global health problem”
“Climate change is one of the greatest global health issues of our time and we have shown that many heat waves have gone largely unnoticed outside of the developed world,” said co-author Dann Mitchell, professor of climate sciences at the University of Bristol. A heat wave can mean thousands of deaths for a country. Countries where temperatures are already outside the normal and well-tolerated range are the most vulnerable.
Using climate model projections, scientists also drew conclusions about developments over the century. The analysis therefore confirms predictions that the intensity of heat waves will increase as global temperatures increase. 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 to parts of Australia and Central Africa, for example.
It should 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.