The Heat Dome Boiling Northwest U.S. Already Has Clear Climate Link

It looked like a mistake several days ago when weather models began forecasting temperatures of approximately 115° Fahrenheit heat in Portland, Oregon. Then it happened. The National Weather Service has now recorded 116°F (46.7°C) at the Portland International Airport.

The heat in the Pacific Northwest is unprecedented but the dynamics involved are straightforward. Summertime heat warms air above the ground or ocean, which then rushes up into the atmosphere to create a dome air that blocks new systems from moving in. That’s how the term “heat dome” has become a newly present part of the climate vocabulary in the U.S and Canada.

Carl Schreck, a research scholar at North Carolina State University, says the dome’s high-pressure can push the jet stream to the north—in this case into northern Canada—causing it to slow down. Eventually, the formation basically becomes “too big to keep standing and it falls over,” Schreck says, releasing its air load to the south. 

Until that happens, the heat is trapped—as are the people who must cope beneath it.

The Heat Dome Boiling Northwest U.S. Already Has Clear Climate Link

President Joe Biden connected extreme heat in the Northwest to rising greenhouse gas emissions. “As climate change induces extreme weather events more and more frequently, we need to make investments to build a more resilient grid,” he said Tuesday in a speech in La Crosse, Wisconsin, calling for passage of an infrastructure deal he struck with a bipartisan group of senators.

No heat dome on record has ever baked normally mild Portland into Phoenix-like conditions. The city’s record high before Sunday was 107°F, last reached in 1981. Topping that mark was unlikely. Beating it by five degrees was even more unlikely, until it happened on Sunday. And beating that new mark again by 4°F was unspeakable. Until it happened on Monday.

“Usually, the correct-enough intuition to meteorologists is to say, ‘yeah, something's wrong’ or ‘there's some bug in the code,’” says Daniel Swain, a climate scientist at UCLA who studies how extreme events are changing on a warming Earth. This time, however, there was no mistake. When thermometers in Portland reached 116°F on Monday, it was a victory for weather models and no one else.

Heat domes occur naturally and are not necessarily tied to climate change beyond the fact that our hotter climate is raising both average and extreme temperatures everywhere. Scientists no longer study whether climate change affected the intensity of a heatwave—they study how much it did so. 

In fact, climate change routinely intensifies many extreme weather patterns to the point that scientists can now estimate its influence nearly in real time. World Weather Attribution, a scientific partnership that conducts climate analyses while events are occurring or immediately after, is currently examining the ongoing Pacific Northwest heatwave. Scientists have run so many heatwave analyses in recent years that they have been able to  standardize what, in the scheme of things, is still a fairly recent development.

Swain, who trained as both a meteorologist and a climate scientist, calls the Pacific Northwest heat dome “mind-blowing.” Hot spells generally stand out because they max out a single metric, such as a record daytime high, duration, high nighttime temperatures. Not so with the heatwave across the Western U.S.

“In this case, all of those things are literally off the charts,” he says. “There really aren’t any records that this heatwave isn’t breaking.”

Climate change may even have a role in the persistence of the heat itself. A team of U.S. and European researchers suggested in a scientific journal in 2018 that the Northern Hemisphere can develop a rigid, wave-like atmospheric circulation pattern that locks sometimes devastating weather systems in place. Such a pattern has been in place for the last several weeks, and instances may increase by 50% as temperatures rise this century.

By missing these patterns, modelers are unable to see the extent of climate change’s influence. “In that sense,” says Michael Mann, professor of atmospheric science at Penn State University and lead author of the 2018 paper, “climate models are actually underestimating the impact that climate change is having on events like the unprecedented heatwave we’re witnessing out West right now.”

The bad news won’t let up when the heat dome gives way. Extreme heat in the Pacific Northwest will intensify the effects of the drought in the region, warns Erica Fleishman, director of the Oregon Climate Change Research Program. The heatwave will also add to the threat of wildfires as vegetation dries out and winds becoming stronger. Last year’s wildfires in Oregon, even without record-breaking high temperatures, burned 1.2 million acres, destroyed over 5,000 homes and is estimated to cost the state $622 million in  cleanup costs, according to a January report from the state.

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