Pacific Northwest heat wave would have been “virtually impossible” without climate change, experts say – .

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Pacific Northwest heat wave would have been “virtually impossible” without climate change, experts say – .


Just a week ago, the Pacific Northwest – a place normally known for its cool and humid climate – suffered the most extraordinary heatwave never seen there in modern times. Even seasoned meteorologists couldn’t believe what they saw as seemingly impossible heat persisted day after day.
Portland, Ore., Climbed 116 degrees, breaking an all-time record of 9 degrees. Lytton, Canada, broke that nation’s all-time record three days in a row, peaking at 121 degrees. The next day, 90% of the city burnt to the ground as more than 100 forest fires ravaged British Columbia. Officials say several hundred people have been killed in the heat, and that number is expected to rise once assessments are completed.

The extreme heat wasn’t just unusual – it would have been “virtually impossible without man-made climate change,” according to a new analysis by 27 climatologists from the World Weather Attribution Network. And the study warns, “As warming continues, it will become much less rare. “

The network is a collaboration of scientists seeking to understand the link between extreme weather conditions and climate change. State-of-the-art scientific techniques allow them to quickly analyze an extreme weather event and determine the extent to which climate change made in.

The article concludes that the chances of a heat wave of this magnitude occurring in the absence of climate change are so incalculable that they would have been “virtually impossible” otherwise.

Even in today’s warmed climate – where average global temperatures have risen by 2 degrees Fahrenheit since pre-industrial times – analysis reveals that this heat wave is a 1,000-year event. Discovery verifies CBS News estimate reported last week as scientists took stock of the record heat.

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The core of the thermal dome, as measured by the thickness of the air column over British Columbia and the Pacific Northwest, is equivalent – statistically speaking – to an event over 1,000 years.
CBS News

In addition, the World Weather Attribution team also found that climate change made this heat wave at least 150 times more likely and almost 4 degrees hotter than it would have been before humans started to warm up. the climate in the 1800s.

Perhaps even more concerning are their conclusions about our future. The team found that if the Earth continues to warm on its current path, and by mid-century, we will exceed the Paris Climate Agreement target of limiting warming to 2 degrees Celsius ( 3.6 degrees Fahrenheit), then heat waves of this magnitude will no longer be 1- 1000-year events – they will occur once every 5-10 years.

“Our findings provide a strong warning: our rapidly warming climate is taking us to uncharted territory that has important consequences for health, well-being and livelihoods. Adaptation and mitigation are urgently needed to prepare societies for a very different future, ”the document said. States.

“What we are seeing is unprecedented”

Even seasoned scientists who regularly study the link between extreme weather and climate change, like study co-author Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute, were shocked to see how out of bounds the recent heat wave was.

In email correspondence with CBS News, Oldenborgh said, “We totally agree with the meteorologists. Last year, we would have said that a heat wave of this magnitude would have been impossible. It appeared that the heatwaves were doing well, with temperatures gradually rising with global warming, about twice as fast as the global average temperature. And then we have this. “

CBS News asked him what the chances were that a heat wave of this magnitude had occurred before man-made climate change. His estimate is surprising: “larger than very roughly [once per] 150,000 years old. “

Equally astonished was study co-author Dr Friederike Otto of the University of Oxford. “What we are seeing is unprecedented. You are not supposed to break records of seven to nine degrees Fahrenheit. It is such an exceptional event that we cannot rule out the possibility that we are experiencing extreme temperatures today that we only expected to arrive at higher levels of global warming, ”said Otto.

In order to arrive at these conclusions, the team studied the high temperatures from Sunday June 27 to Tuesday June 29, in an area centered on the Pacific Northwest, including Vancouver, Canada; Seattle and Portland – an area of ​​about 9 million people.

The dots in the graph below represent how many degrees (Celsius) each weather station has broken its daily record.

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Global weather attribution study

The study involved two approaches. The first was a statistical analysis of the likelihood that an event of this magnitude was based on historical data. The second method used advanced climate models to determine what the chances of a heat wave like this would be without the warming caused by man-made climate change.

In both cases, this event far exceeded the limits of a normal climate, meaning that it would be virtually impossible without human influence on the climate.

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The images show a time series of the hottest days of each year since the mid-1900s in Seattle (top) and Portland (bottom). The 2021 heatwave extremes in both cases are well outside normal limits in a natural climate.
Global weather attribution study

Perhaps most surprisingly, however, is that such an extreme event, even in our current hot climate, is only expected to occur once every 1,000 years. This means that either the Pacific Northwest heat wave was incredibly unlucky, or science still hasn’t figured out how climate change is impacting such extreme weather conditions. This is the conclusion favored by some of the authors of the article.

“As we expect heat waves to become more frequent and intense, it was unexpected to see such levels of heat in this region. This raises serious questions about whether we really understand how climate change is making heatwaves hotter and deadlier, ”Oldenborgh said.

Dim Coumou, also from the Royal Netherlands Meteorological Institute, agrees: “This event should be a big warning. Currently, we do not fully understand the mechanisms that led to such exceptionally high temperatures.

But Coumou goes further, assuming that humans have warmed the planet so much that the impacts are now escalating beyond mere cause and effect.

“We may have crossed a threshold in the climate system where a small amount of additional global warming causes temperature extremes to rise more rapidly,” he said.

In the article, the authors point out that climate change makes “every” heat wave more intense. The image below, taken from the study, shows that the trend for the highest daily temperatures (in degrees Celsius) is increasing in almost all regions of the world.

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Global weather attribution study

The heat wave was caused by a generally strong ridge of high pressure, which looks like a mountain of hot air, stacked vertically in the atmosphere. This ” heating dome Was stranded over the area for a week, stuck in an atmospheric traffic jam known as the Omega Block.

Below this thermal dome ridge occurs a downward movement, which tends to compress and heat the air. Local effects also contributed, such as a wind coming down from the mountains, which acts in the same way, compressing and warming the air. These effects are typical of heat waves.

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An Omega block and an undulating jet stream kept the heat in place over the Pacific Northwest.
CBS News

But the bigger question is whether the thermal dome was made more likely by our now warmer climate? In other words, has climate change altered the direction currents of the northern hemisphere, making the jet stream slower and more wavy, allowing those stuck thermal domes to become more current? The theory, called Quasi Resonant Amplification, was put forward by the attribution team but was not analyzed in this study.

however, Dr Michael Mann, a famous Penn State climatologist who studied and invented the terminology, is sure it played a role.

“The report highlights why these attribution analyzes are ultimately limited in terms of the conclusions that can be drawn. They recognize that the models used do not capture the phenomenon of the jet stream (resonant planetary amplification) which WE KNOW played an important role in this event, promoting the intensity and persistence of the heating dome, ”said Mann. .

While there are various and complex factors that came together to amplify this specific event, a NASA scientist Dr Peter Kalmus says the extreme heat wave is proof of our escalating climate crisis.

“Climate impacts, including heat, fire and drought are hitting us now. They are like punches to our civilization and they will continue to come both faster and stronger. These and other impacts will continue to intensify as long as we burn fossil fuels, ”said Kalmus.

The study’s authors agree and say the finding is straightforward: “Until global greenhouse gas emissions are stopped, global temperatures will continue to rise and events like these will continue to rise. will become more frequent. “

Kalmus takes it a step further, telling CBS News, “If you think about it, there is no way to adequately prepare for these impacts. The only reasonable option is to do whatever it takes to end the fossil fuel industry completely in the short term. We need strong policies, but we also need the public to realize how urgent this is in order to get those policies. ”



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