Scientists identify the most extreme heat waves ever recorded

Scientists have identified the most extreme heat waves ever recorded globally, some of which went almost unnoticed when they occurred decades ago.

According to experts from the University of Bristol, the most extreme heat wave ever occurred was in the southeast Asia in April 1998.

Meanwhile, the western North American heatwave last summer was only the sixth most severe heatwave.

Last year’s North American heat wave saw an all-time Canadian high of 49.6 ° C (121.3 ° F) in Lytton, British Columbia on June 29.

For their research, the experts used a method that calculates how much extreme heat waves are relative to local temperature, rather than just where mercury readings were the highest.

Map showing the magnitude of the extreme maximum since 1950 in each region, expressed in terms of deviation from mean temperatures, with the trend towards climate change removed. Darker colors indicate greater extremes

Map showing the magnitude of the extreme maximum since 1950 in each region, expressed in terms of deviation from mean temperatures, with the trend towards climate change removed. Darker colors indicate greater extremes

THE MOST EXTREME HEAT WAVES EVER

1. Southeast Asia (April 1998)

2. Southern Brazil (November 1985)

3. Southern United States (July 1980)

4. Southwestern Peru (January 2016)

5. Alaska (July 2019)

6. North America (June 2021)

According to the study authors, heat waves are expected to get warmer in the future as climate change worsens.

Earlier this year, the Met Office raised the heat wave threshold for eight English counties, as the levels are designed to be relative to the current climate.

“The recent heatwave in Canada and the United States has shocked the world,” said lead author of the study, climatologist Dr Vikki Thompson of the University of Bristol.

Yet we show that there have been some even greater extremes in the past few 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 West North American heatwave was the deadliest weather event ever recorded in Canada, causing hundreds of deaths.

The associated violent fires have also led to extensive infrastructure damage and crop losses.

For the study, the researchers classified heat waves in relation to the local temperature at which they occurred, based on the fact that events so far from their natural variability are likely to be more “extreme.”

HEAT WAVE: MET OFFICE DEFINITION

A heat wave is a long period of heat relative to the expected conditions of the area at that time of year, which can be accompanied by high humidity.

A UK heatwave threshold is reached when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold.

The threshold varies by county in the UK.

The results showed that the top three hottest locations ever were in Southeast Asia in April 1998, Brazil in November 1985, and the southern United States in July 1980.

Southeast Asia in April 1998 reached 91 ° F (32.8 ° C), while Brazil peaked at 97.7 ° F (36.5 ° C) in November 1985 and the southern United States in July 1980 they reached 101.1 ° F (38.4 ° C).

So even though Southeast Asia in April 1998 didn’t have as high mercury values ​​as others, it was “the most extreme” as it was out of local variability as an indicator of potential harm.

“The heatwave of western North America will be remembered because of its widespread devastation,” said Dr. Thompson.

However, the study exposes several major weather extremes over the past few decades, some of which have largely gone under the radar, possibly due to their presence in more disadvantaged countries.

‘It is important to assess the severity of heat waves in terms of local temperature variability, because both humans and the natural ecosystem will adapt to this.

“So in regions where there is less variation, a smaller absolute extreme can have more damaging effects.”

Smoke and flames are seen during the Sparks Lake fire in British Columbia's Thompson-Nicola Regional District amid extreme weather in 2021

Smoke and flames are seen during the Sparks Lake fire in British Columbia’s Thompson-Nicola Regional District amid extreme weather in 2021

The team also used sophisticated climate model projections to anticipate heat wave trends over the rest of this century.

Levels indicated by heatwave intensity patterns will increase in line with rising global temperatures.

While higher local temperatures don’t necessarily cause the greatest impacts, they are often interrelated.

Improving understanding of climatic extremes and where they occurred can help prioritize measures to help address this problem 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) in Lytton, British Columbia on June 29, 2021.

“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 outside the developed world have gone largely unnoticed.

“The nationwide heat burden on mortality can be thousands of deaths, and countries experiencing temperatures outside their normal range are the most susceptible to these shocks.”

The new findings were published today in Science Advances.

ENGLAND WARM UP! MET OFFICE INCREASES HEAT WAVE TEMPERATURE THRESHOLD IN EIGHT COUNTRIES IN RESPONSE TO CLIMATE CHANGE

Temperatures needed for a heat wave to be officially declared have been raised in eight British counties, the Met Office announced in March.

Heatwaves are called when an area has at least three consecutive days with daily highs reaching or exceeding a certain temperature threshold.

Levels are designed to be relative to the current climate, but how global warming is pushing UK temperatures higher, the thresholds have now increased for eight UK counties ahead of the summer months.

The eight counties are Surrey, Berkshire, Buckinghamshire, Bedfordshire, Hertfordshire, Cambridgeshire, Lincolnshire and East Riding of Yorkshire.

Read more: The heatwave threshold has increased in eight counties as the climate warms