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What to know as climate change drives extreme heat

by David Sherfinski | @dsherfinski | Thomson Reuters Foundation
Wednesday, 7 July 2021 22:21 GMT

Shanton Alcaraz from the Salvation Army Northwest Division gives bottled water to Eddy Norby who lives in an RV and invites him to their nearby cooling center for food and beverages during a heat wave in Seattle, Washington, U.S., June 27, 2021. REUTERS/Karen Ducey

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As heatwaves smash records and claim lives - including in unexpected places like Canada and the U.S. Pacific Northwest - climate scientists explain what's happening and why

By David Sherfinski

WASHINGTON,  July 7 (Thomson Reuters Foundation) - An unprecedented heatwave that smashed heat records in the U.S. Pacific Northwest and western Canada in late June has shaken climate scientists, who say they are now unsure where or how often such killer heat might be repeated.

But such an extreme event would be at least 150 times rarer without the influence of climate change, they said in a rapid assessment study released Wednesday, a little over a week after the heatwave, which is thought to have left hundreds dead.

Here's what they say we know - and don't - about worsening extreme heatwaves and how widespread they might become:



Why is the recent "heat dome" event in the U.S. Pacific Northwest and Canada so significant?

The rapid spike in temperatures was well above what scientists thought was possible, even factoring in 1.2 degrees Celsius of global warming since pre-industrial times.

“It was way above the upper bound," of predictions, said Dutch climate scientist Geert Jan van Oldenborgh, a co-author of the study produced by the World Weather Attribution group, which aims to pinpoint the role of climate change in extreme weather. 

“It’s rather surprising and shaking that our theoretical picture of how heatwaves behave was broken so quickly,” said the Royal Netherlands Meteorological Institute scientist.

In late June, Portland, in the U.S. state of Oregon, hit 46.7 degrees Celsius (116 Fahrenheit), topping its previous heat record a whopping 5C. Seattle, further north, passed its former record by 8C and Vancouver, in Canada, by 3.8C.

Normally records are passed by fractions of a degree, scientists said. The U.S. and Canadian June heatwave was "by far the largest jump in the record we've ever seen", said Friederike Otto of the University of Oxford.

Hardest hit was the British Columbia village of Lytton which broke Canadian temperature records three days in a row - hitting 49.6C (121F) on June 29 - before being largely destroyed by a heat-fueled wildfire.

What made the heatwave happen?

With drought and dry soils known to enhance heat, a particularly dry spring in the region is "kind of an obvious smoking gun" as a contributor, Van Oldenborgh said.

Scientists are also looking at whether changes in the jetstream of atmospheric air currents or in ocean circulation patterns might have played a role.

But the World Weather Attribution (WWA) study said the sudden heat spike is mainly the result of human-driven climate change, and would have been "impossible" without it.

“For heatwaves, climate change is an absolute game changer,” said Otto, a co-leader of the group.

What does an event that no model saw coming mean for our ability to understand what climate change might bring?

"It's a strong warning we need to study heatwaves more," Otto said, as it showed existing models "are really not a good indicator of what is to come, even at 1.5 degrees", the lower warming limit set in the Paris Agreement on climate change.

Scientists now are much less clear on how climate change will impact heatwaves than they were just weeks ago, and "we should definitely not expect heatwaves to behave as they have in the past", she warned.

Van Oldenborgh admitted that "a lot of people are very worried about this event", noting "it was a very, very, very rare event but we cannot really say with any certainty how rare it was".

Could that kind of heatwave happen in other places?

Yes - and lesser heat records are already being set each year in many places in the world as climate-changing emissions continue to rise, the scientists said.

"Really what everyone needs to take from (the) study - whether they are in British Columbia or Washington or somewhere else in the world - is that how the impacts of climate change manifest today is to a large degree a stronger intensity and frequency of heatwaves,” Otto said.

Scientists say dramatically strengthening heatwaves could bring "cascading risks". What do they mean by that?

Power shortages are often a threat during severe heatwaves, as demand for power to run air conditioners and fans surges, leaving people unexpectedly without cooling in dangerous temperatures.

Glacial ice can melt faster in extreme heat, raising the risk of flooding, and wildfires are more likely to get out of control in very hot, dry conditions, scientists say.

"We’ve seen cases of compound risks (where) smoke from wildfires led to the advice to keep windows closed – which, of course, makes it even hotter inside," noted climate scientist Maarten van Aalst, another co-author of the WWA study.

How do heatwaves rank as a risk compared to other disasters, from floods to storms?

In the United States - and globally - extreme heat causes more deaths than any other weather-related disaster, the scientists said.

study published Wednesday in The Lancet Planetary Health journal said high temperatures are now killing over 600,000 people a year globally, including an average of 224,000 in Asia, 179,000 in Europe and 18,750 in the United States.

Van Aalst said awareness is growing of the seriousness of heatwave threats, including among disaster responders like the International Federation of Red Cross and Red Crescent Societies.

“It has risen to the top of our concerns, compared to say two decades ago,” said Van Aalst, director of the Red Cross Red Crescent Climate Centre.

How can we reduce the risks?

Researchers said public alert systems, making sure buildings and cities are better designed for cooling and raising awareness of the threats - including reminding elderly people to stay hydrated when temperatures spike - all can help.

Seattle, scorched by the June heatwave, has the least air conditioning of any U.S. city - an example of how heatwaves may be particularly damaging for places that haven't considered themselves at risk previously and now need to prepare, Van Aalst said.

“This is going to get worse, so it’s a combination of that sort of small-scale local preparedness on short time scales and longer-term adaption of our cities and our houses,” he added.

The most important way to tackle worsening heatwaves, however, is by swiftly eliminating use of fossil fuels so temperatures increases don't continue to accelerate, scientists said.

"Our emissions have risen much faster in recent years, global mean temperature has risen much faster in recent years," Otto said. "That we see more extreme heat and more records broken is totally expected."

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(Reporting by David Sherfinski ; editing by Laurie Goering : (Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters. Visit http://news.trust.org/climate)

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