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Study: Climate change is increasing the frequency and temperature of extreme heat waves

Hayley Smith, Los Angeles Times on

Published in News & Features

LOS ANGELES — As California awakens to the worsening risk of extreme climate events, researchers are shedding new light on last year's anomalous and extreme Pacific Northwest heat wave. One study published this week said such heat waves could become 20 times more likely to occur if current carbon emissions continue unabated. Another said they may also be nearly 10 degrees hotter.

The nine-day event in late June and early July 2021 seared parts of Northern California, Oregon, Washington and British Columbia, where Canada saw its highest temperature on record, 121.3 degrees. The heat wave claimed hundreds of lives, sparked several devastating wildfires and killed an estimated 1 billion sea creatures.

Such an event would have been "virtually impossible" in the 1950s, but atmospheric warming has already increased its probability to about a 0.5% chance per year, according to one study out of Columbia University, published Thursday in the journal Nature Climate Change. Should warming surpass 2 degrees Celsius — the upper limit set by the International Panel on Climate Change — that probability could soar to a 10% chance per year as soon as 2050.

"The single biggest control on how bad heat waves will get — in excess of how bad they already currently are — is the amount of CO2 that we put into the atmosphere," said Samuel Bartusek, a Ph.D. student at Columbia's Lamont-Doherty Earth Observatory and the lead author of the study. "There's really only one solution to the problem of putting more carbon dioxide into the atmosphere, which is to stop doing it."

Bartusek said the extraordinary heat wave was "shocking" both for the people who experienced it and for the scientific community, which is why researchers hope to gain a better understanding of its physical mechanisms and its relationship to climate change.

"This was an extremely weird event," said Michael Wehner, a climate scientist at the Lawrence Berkeley National Laboratory who co-authored another paper on the heat wave published last week in the journal Geophysical Research Letters. "It was also tragic, of course, because of the mortality that resulted from it."


Among other conclusions, that paper found that the heat wave was so unprecedented it essentially broke most of the standard tools used to measure the human influence on heat waves.

"At the end of the day, we calculated not only was the event impossible without climate change — it was impossible with climate change. And of course, it happened, so that means that the model is wrong," Wehner said.

Wehner said such statistical outliers make it difficult to forecast the future frequency of such events with certainty. However, his paper does include findings about temperature, noting that global warming caused as much as a 1.8 degree increase in maximum temperatures during the heat wave.

Future warming could lead to a roughly 9 degree increase in heatwave temperatures by the end of the 21st century, the paper says.


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