Climate models

North American heatwave broke records


Climatologists have been shocked by recent deadly heat waves in western Canada and the northwestern United States, which have exceeded all global heating forecasts

Climate scientists have warned that the world is already experiencing episodes of extreme heat that are only expected to occur on a much hotter planet.

The extraordinary heat that engulfed northwestern Canada and the United States last week broke temperature records by several degrees, with temperatures exceeding 40 ° C for days and reaching 49.6 ° C in the village of Lytton, Canada.

Soon after, Lytton was destroyed in forest fires. In Western Canada, nearly 500 people are estimated to have died and experts expect the death toll to rise.

Without the influence of man-made climate change, the heat wave would have been “virtually impossible,” according to a rapid attribution analysis by an international team of 27 leading climatologists who have worked tirelessly to publish the study.

Climate change, they found, has made the heat wave at least 150 times more likely to occur – such extreme heat not occurring according to current statistical analyzes.

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The results have prompted scientists to question their understanding of the impact of climate change on heat waves, which could lead to the revision of some climate models.

Friederike Otto, from the Environmental Change Institute at the University of Oxford, one of the study’s authors, said climate science has been “a little complacent” about how it understands sea waves. heat.

The intensity of heat waves is increasing in orders of magnitude not seen for other extreme events, she said. “Heat waves are how climate change is killing us. This is how climate change manifests itself more strongly.

Using computer observations and stimulation, the scientists compared the past climate in the region covering Portland, Seattle and Vancouver with current trends after global warming of around 1.2 ° C since the end of the 19th century.e century.

They found that the temperatures during last week’s event were so extreme that it was difficult to estimate with certainty how rare the event was, but suggested that it amounted to a single event in a thousand. years in the current climate.

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Geert Jan van Oldenborgh of the Royal Netherlands Meteorological, another of the authors, told reporters that the heat wave had shattered previous temperature records of up to 5 ° C – “an extraordinary event”.

“For comparison, here in the Netherlands we were really shocked when the previous record was broken by 1.8 ° C and it’s more than double. “

The heat wave, said Van Oldenborgh, is “both a major disaster and weather event, but also a major scientific challenge to understand what happened.”

He said the state of climate science in 2020 would have shown that the heat wave was “fundamentally impossible” and that more research was needed to understand how it happened and whether such an event could occur in other parts of the world.

“It’s rather shaking that our theoretical picture of heat wave behavior has been shattered so brutally,” he said. “We are much less certain of how the climate [change] affects heat waves than we were two weeks ago.

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The authors of the article identified two possible explanations for the extreme jump in maximum temperatures observed in North America.

The first is ‘really bad luck’ and that, although exaggerated by climate change, it remains a very low probability event. However, in a future world characterized by global warming of 2 ° C, such an extreme heat wave could occur once every 5 to 10 years, according to the study.

Another explanation is that the climate system in this region has crossed a threshold that has increased the likelihood of such extreme heat well beyond the gradual rise in temperature peaks that have been observed so far.

In this scenario, record-breaking heat waves like last week’s event are already more likely to occur than climate models predict – which the team of scientists says needs further investigation.

“This is such an exceptional event that we cannot rule out the possibility that we are facing extreme heat today that we only expected to reach higher levels of global warming,” said Otto.

If this second scenario turns out to be correct, it could lead to the revision of climate models.

If an essential climate process is missing from current climate models, these will “definitely need to be improved,” Van Oldenborgh said.


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