Most extreme heat waves of recent decades identified
Climate change means that heat waves are more severe. However, some past events have not attracted media attention. And yet there were some extreme examples.
For weeks, people in South Asia have been suffering from a severe heat wave. On some days, the air temperature regionally reaches 50 degrees Celsius. Even at night, it hardly cools down at all, which puts a strain on health and is likely to lead to numerous deaths. The heat wave in India and Pakistan is one of a series of extreme weather events of this kind: In the summer of 2021, the northwestern U.S. and western Canada were sweltering, and in early 2022, thermometers in Argentina rose to record levels. A study by Vikki Thompson of the University of Bristol and her team in Science Advances identified some of the most extreme heat waves in recent decades, some of which received little media attention.
For example, the temperature rose to 49.6 degrees Celsius in Lytton, Canada, on June 29, 2021, beating the previous record in the region by 4.6 degrees Celsius. The highest daily average was still 39.5 degrees Celsius. However, this event was trumped by several heat waves in which the standard deviation from the average temperatures for the respective seasons was even higher than in Canada. Southeast Asia in April 1998 at 32.8 degrees Celsius, Brazil in November 1985 at 36.5 degrees Celsius, and the southern U.S. in July 1980 at 38.4 degrees Celsius (maximum temperature in each case) all exceeded the previous peaks for these regions by more than five units in some cases: notable jumps, in other words, even if the maximum temperatures remained below those in Canada or currently in South Asia.
"The heat wave in western North America will be remembered for its extreme consequences. However, our study reveals several major meteorological extremes in recent 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 variability, as both humans and natural ecosystems adapt to it. Therefore, in regions with less variability, even a smaller absolute maximum can have a more severe impact," Thompson says.
The team also used their model to calculate how heat waves might evolve in the future with climate change. "We found that extreme heat events are likely to increase over the next century, at the same rate as the local average temperature," Thompson says. It's a risk that some climate scientists have already warned about; after all, severe heat waves are among the most dangerous extreme weather events. The summer of 2003, for example, caused thousands of deaths in Western Europe because it barely cooled down for weeks in some places.
The 2021 heat wave is Canada's worst weather event to date, with several hundred deaths. In addition, the heat exacerbated the region's long drought, which ultimately caused devastating wildfires that incinerated the town of Lytton shortly after the record was set.
Spectrum of Science
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