Scientists identify the most extreme heatwaves ever recorded

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

According to experts at the University of Bristol, the most extreme heat wave ever hit Southeast Asia in April 1998.

Meanwhile, the heat wave in western North America last summer was only the sixth most severe heat wave.

Last year’s North American heat wave saw a Canadian peak of 121.3°F (49.6°C) in Lytton, British Columbia, on June 29.

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

Map showing the magnitude of the greatest extreme since 1950 in each region, expressed in terms of deviation from average temperatures, removing the trend of climate change.  Darker colors indicate greater extremes

Map showing the magnitude of the greatest extreme since 1950 in each region, expressed in terms of deviation from average temperatures, removing the trend of climate change. Darker colors indicate greater extremes

MOST EXTREME HEAT WAVES EVER

1. Southeast Asia (April 1998)

2. Southern Brazil (November 1985)

3. Southern USA (July 1980)

4. Southwest Peru (January 2016)

5. Alaska (July 2019)

6. North America (June 2021)

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

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

“The recent heat wave in Canada and the United States shocked the world,” said lead researcher, climate scientist Dr Vikki Thompson of the University of Bristol.

‘Yet we show that there have been even greater extremes in recent decades.

‘Using climate models, we also see that extreme heat is likely to increase in magnitude over the next century – at the same rate as the local average temperature.’

The 2021 heat wave in western North America was the deadliest weather event ever in Canada, resulting in hundreds of deaths.

The raging wildfires that accompanied it also led to extensive damage to infrastructure and loss of crops.

For the study, researchers ranked heat waves in proportion to the local temperature of where they occurred, based on the fact that events that far out of their natural variability are arguably more “extreme.”

HEATWAVE: WITH OFFICE DEFINITION

A heat wave is an extended period of warm weather relative to the area’s expected conditions at that time of year, which can be associated with high humidity.

A UK heat wave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures reaching or exceeding the heat wave temperature threshold.

The threshold varies by county in the UK.

Results showed that the top three hottest ever was in Southeast Asia in April 1998, Brazil in November 1985 and the southern US 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 in July 1980. 1°F (38.4°C).

So while Southeast Asia didn’t register as high on mercury levels as others in April 1998, it was “most extreme” because it was outside of local variability as an indicator of possible damage caused.

“The heat wave in western North America will be remembered for its widespread devastation,” said Dr. Thompson.

However, the study uncovers a number of larger meteorological extremes in recent decades, some of which have remained largely under the radar, likely due to their occurrence in more deprived countries.

“It is important to assess the severity of heat waves in terms of local temperature variability, as 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 harmful effects.”

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

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

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

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

The modeling indicated that levels of heat wave intensity will increase in line with increasing global temperatures.

While the highest local temperatures do not necessarily cause the greatest effects, they are often related.

Improving understanding of climate extremes and where they have occurred could help prioritize action to address them in the most vulnerable regions, they say.

The temperature in Lytton, about 250 kilometers east of Vancouver, reached 49.6°C on June 29, 2021 in Lytton, British Columbia.

The temperature in Lytton, about 250 kilometers east of Vancouver, reached 49.6°C on June 29, 2021 in Lytton, British Columbia.

The temperature in Lytton, about 250 kilometers east of Vancouver, reached 49.6°C on June 29, 2021 in Lytton, British Columbia.

“Climate change is one of the biggest global health problems of our time,” said study co-author Dann Mitchell, a professor of climate science at the University of Bristol.

“We have shown that many heat waves outside the developed world have gone largely unnoticed.

“The burden of heat on country-level mortality can amount to thousands of deaths, and countries with temperatures outside their normal range are most susceptible to these shocks.”

The new findings are published today in Science Advances.

ENGLAND IS WARMING! WITH OFFICE INCREASES HEAT WAVE TEMPERATURE THRESHOLD IN EIGHT COUNTIES IN RESPONSE TO CLIMATE CHANGE

Temperatures needed to officially declare a heat wave have risen in eight English counties, the Met Office announced in March.

Heat waves are called when an area has at least three days in a row with daily maxima that reach or exceed a certain temperature threshold.

Levels are designed to be relative to the current climate, but as global warming is pushing up temperatures in the UK, thresholds have now been raised for eight English counties ahead of the summer months.

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

Read more: Heat wave threshold is raised in eight counties as climate warms

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