WORLD / AMERICAS
N.America heat wave ‘virtually impossible’ without climate change: study
Hottest June on record sounds alarm
Published: Jul 08, 2021 06:42 PM


People enjoy themselves at a beach under the heat wave warning at English Bay in Vancouver, British Columbia, Canada, June 24, 2021.Photo:Xinhua

People enjoy themselves at a beach under the heat wave warning at English Bay in Vancouver, British Columbia, Canada, June 24, 2021.Photo:Xinhua


A record-breaking heat wave that hit the western US and Canada at the end of June would have been "virtually impossible" without the impact of human-caused climate change, according to an analysis by a group of leading climate scientists.

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

Pacific Northwest areas of the two countries saw temperatures that broke records by several degrees, including a Canadian record of 49.6 C in the village of Lytton in British Columbia, which was subsequently mostly destroyed in a wildfire.

"There's absolutely no doubt that climate change played a key role here," Friederike Otto, a climatologist at the University of Oxford said during a press conference discussing the findings.

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

They found the observations were so extreme that they lie far outside the range of historically observed temperatures. But with the climate of today, it was estimated that the event could take place once in a thousand years.

Looking into the future, if the planet were to warm by 2C - which could happen as early as the 2040s at the current rate - heat waves like these would occur every five to 10 years. 

The heat wave meant that it was the hottest June on record in North America, according to data released by the European Union's climate monitoring service on Wednesday.

The researchers suggested two explanations for how climate change made the stunning heat more likely. The first was that, while climate change made the event more likely to occur, it remains an extreme outlier.

In this explanation, pre-existing drought that deprived the area of evaporative cooling, together with a slow-moving high pressure system in the atmosphere called a "heat dome," were supercharged by climate change.

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

The second hypothesis is more dire: Climate system has crossed a threshold where a small amount of overall global warming is now causing a faster rise in extreme temperatures than has been observed so far.

"Everybody worries about the implications of these events because this is something that nobody saw coming, that nobody thought possible," said co-author Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute. 

"We feel that we do not understand heat waves as well as we thought we did," he said.

AFP