Scientists have identified the most extreme heatwaves ever recorded worldwide, some of which went almost unnoticed when they struck decades ago.
According to experts from the University of Bristol, April 1998 was the most extreme heat wave to date in Southeast Asia.
Meanwhile, the heatwave in western North America last summer was only the sixth most severe heatwave.
Last year’s North American heatwave hit a Canadian all-time high of 49.6°C (121.3°F) on June 29 in Lytton, British Columbia.
For their research, the experts used a method that calculates how extreme heat waves are relative to local temperature, and not just where mercury levels were highest.
Map showing the magnitude of the greatest extreme since 1950 in each region, expressed as deviation from average temperatures, with no climate change trend. Darker colors indicate greater extremes
THE MOST EXTREME HEAT WAVES OF ALL TIME
1. Southeast Asia (April 1998)
2. Southern Brazil (November 1985)
3. Southern US (July 1980)
4. Southwest Peru (January 2016)
5. Alaska (July 2019)
6. North America (June 2021)
According to the study’s authors, heat waves are projected to get hotter in the future as climate change worsens.
Earlier this year, the Met Office raised the heatwave threshold for eight English counties because the levels are relative to the current climate.
“The recent heatwave in Canada and the United States has rocked the world,” said the study’s lead author, climate scientist Dr. Vikki Thompson from Bristol University.
“Nevertheless, we show that there have been some even greater extremes in recent decades.
“Using climate models, we also find that extreme heat events are likely to increase in magnitude over the next century – at the same rate as the local average temperature.”
The 2021 western North American heatwave was the deadliest weather event on record in Canada, killing hundreds.
The associated raging forest fires also led to extensive damage to infrastructure and crop failures.
For the study, the researchers ranked heatwaves relative to the local temperature at which they occurred, on the basis that events so far outside their natural variability are arguably more “extreme.”
HEATWAVE: OFFICE DEFINITION MET
A heat wave is a prolonged period of hot weather compared to the area’s expected conditions at that time of year, which may be accompanied by high humidity.
A UK heatwave threshold is reached when a location experiences a period of at least three consecutive days with daily high temperatures that meet or exceed the heatwave temperature threshold.
The threshold varies by UK county.
Results showed that the three hottest times on record were in Southeast Asia in April 1998, Brazil in November 1985, and the southern United States in July 1980.
Southeast Asia reached 91°F (32.8°C) in April 1998, while Brazil peaked at 97.7°F (36.5°C) in November 1985 and the southern US reached 101.1°F in July 1980 (38.4 °C).
So, while Southeast Asia was not as high as others in April 1998 for mercury levels, it was “most extreme” because it was outside of local variability as an indicator of potential damage.
“The heatwave in western North America will be remembered for its widespread devastation,” said Dr. Thompson.
“However, the study uncovers several major meteorological extremes over the past few decades, some of which have largely remained under the radar, likely due to their occurrence in poorer countries.
“It is important to assess the severity of heatwaves based on local temperature variations, as both humans and the natural ecosystem will adapt to them.
“In regions where there is less variability, a smaller absolute extreme can have more damaging effects.”
Smoke and flames are seen during the Sparks Lake wildfire in the Thompson-Nicola Regional District, British Columbia, amid extreme weather in 2021
The team also used sophisticated climate model projections to predict heatwave trends for the rest of the century.
The heatwave intensity indicated by the modeling will increase in line with rising global temperatures.
Although the highest local temperatures do not necessarily have the greatest impact, they are often related.
A better understanding of climate extremes and where they have occurred can help prioritize actions to address them in the most vulnerable regions, they say.
The temperature in Lytton, which is about 155 miles east of Vancouver, reached 49.6 °C (121.3 °F) on June 29, 2021 in Lytton, British Columbia.
“Climate change is one of the biggest global health problems of our time,” said co-author Dann Mitchell, professor of climate science at the University of Bristol.
“We have shown that many heatwaves have gone largely unnoticed outside the developed world.
“The burden of heat mortality at the country level can amount to thousands of deaths, and countries that experience temperatures outside their normal range are the most vulnerable to these shocks.”
The new findings were published today in Science Advances.
ENGLAND HEATS UP! MET OFFICE RAISES HEATWAVE TEMPERATURE THRESHOLD IN EIGHT COUNTIES IN RESPONSE TO CLIMATE CHANGE
Temperatures required for a heatwave to be officially declared have been raised in eight English counties, the Met Office said in March.
Heat waves are triggered when an area meets or exceeds a certain temperature threshold for at least three consecutive days with daily highs.
The values are designed to be relative to the current climate, but with global warming driving temperatures up in the UK, the thresholds have now increased ahead of the summer months for eight English counties.
The eight counties are Surrey, Berkshire, Buckinghamshire, Bedfordshire, Hertfordshire, Cambridgeshire, Lincolnshire and the East Riding of Yorkshire.
Read more: Heatwave threshold will be raised in eight counties as climate warms