North America heat wave “virtually impossible” without climate change, study finds

Record-breaking heat wave that hit the western United States and Canada at the end of June would have been “virtually impossible” without man-made climate change, according to an analysis by a group of prominent climatologists.

The World Weather Attribution group said that global warming, caused by greenhouse gas emissions, makes the heat wave at least 150 times more likely to occur.

The Pacific Northwest regions of both countries saw temperatures that broke records of several degrees, including a Canadian record of 49.6 degrees Celsius in the village of Lytton, which was then largely destroyed in a forest fire.

“There is absolutely no doubt that climate change has played a key role here,” Friederike Otto, a climate scientist at the University of Oxford, said at a press conference on the results.

To determine if climate change played a role, scientists analyzed historical observations and computer simulations to compare the climate as it is today, after about 1.2 degrees of global warming since the late 1800s. , with the climate of the past.

They found that the sightings were so extreme that they fell well outside the range of historically observed temperatures. But with today’s climate, it was estimated that the event could take place once every thousand years.

Looking to the future, if the planet warmed by 2 degrees – which could happen as early as the 2040s at the current rate – heat waves like these would occur every five to 10 years and would be around one warmer degree.

The heat wave made June the hottest month on record in North America last month, according to data released Wednesday by the European Union’s climate watch service.

People and their pets rest at the Oregon Convention Center cooling station in Portland, Oregon on June 28. | AFP-JIJI

The death toll is not yet known, but it is believed to number in the hundreds.

Researchers have suggested two broad explanations for how climate change has made dizzying heat more likely.

The first was that while climate change has made the event more likely to occur, it remains an extreme outlier.

In this explanation, the pre-existing drought that deprived the zone of evaporative cooling, as well as a slow high atmospheric pressure system called a “heat dome,” were supercharged by climate change.

According to this theory, without the influence of climate change, the maximum temperature would have been about 2 degrees lower.

The second hypothesis is more serious: that the climate system has crossed a threshold where a small amount of global warming is now causing temperature extremes to rise more rapidly than has been observed so far.

“Everyone is really worried about the implications of these events because it is something that no one saw coming and that no one would have believed possible,” said co-author Geert Jan van Oldenborgh of the Institute. Royal Netherlands Meteorological.

“We think we don’t understand heat waves as well as we thought,” he said, adding that it could mean that such temperatures are also possible in other high latitude locations such as the Japan, Northern Europe, the rest of the United States and China.

This means adaptation plans must be designed for temperatures well above the range seen in the past, the team warned.

A wildfire burns over the Fraser River Valley near Lytton, British Columbia on Friday, July 2.  |  BLOOMBERG
A wildfire burns over the Fraser River Valley near Lytton, British Columbia on Friday, July 2. | BLOOMBERG

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