Climate change may cause historic heat waves more often than once every 1,000 years, experts say

The heat wave that hit the Northwest this past weekend and into this week is one for the record books, and likely has links to climate change, experts say.

"This heat wave is simply astounding," said Robert Rohde, Ph.D., lead scientist at Berkeley Earth in California. "The heat wave has brought the largest increases in temperature above normal highs ever measured during summer anywhere in North America. Based on what was normal during the 20th century, a heat wave like this in the Pacific Northwest would be expected to occur no more than once in 1,000 years. Global warming has made events like this more likely, but it should still be considered quite rare."

Portland, Oregon, set a new all-time record high of 116 degrees on Monday, making it the third straight day that the city saw a new all-time record high. Seattle hit a new all-time record high on Monday as well, with temperatures reaching 108 degrees -- its second consecutive day seeing an all-time record high. Multiple weather stations in Washington State reached 118 degrees, the hottest temperature the state has ever recorded.

This heatwave didn't just shatter records in the U.S., but Canada too. There were historic all-time high temperatures from the heatwave in Lytton, British Columbia, which hit a sweltering 121 degrees on Tuesday afternoon – the hottest temperature ever recorded in Canada and the third day of consecutive all-time highs in the city. By comparison, Lytton's temperature went higher than some parts of the Southwest desert, like Las Vegas, where the hottest temperature on record is 117 degrees.

According to the National Weather Service, heat kills more people on average than any other weather disaster in the U.S.

U.S. heat waves have been becoming more frequent, lasting longer and are more intense than ever before -- a clear symptom of climate change. Although this historic heat wave in the Pacific Northwest is quite rare, events like this could start happening more often, according to Zeke Hausfather, Ph.D., director of climate and energy at The Breakthrough Institute.

"Summers in the Pacific Northwest have warmed around [3 degrees Fahrenheit] over the past century, with nearly all of that warming occurring in the years since 1970," Hausfather said. "The heat wave currently occurring in the Pacific Northwest would have been an unusually severe heat wave in the absence of historical warming, but on top of warming, it's blowing past old records for the region."

Hausfather said that due to climate change, a heat wave of this magnitude could occur not once every 1,000 years, but rather, closer to once every 100 years.

"If we continue to increase global emissions, it may be a one-in-10 year event by the end of the century," Hausfather said.

A small increase in the Earth's average temperature can dramatically impact climate extremes, both hot and cold, increasing their chances of occurring exponentially.

"Rare events can have their frequency greatly altered by small changes in the mean," Rohde said. "As the average global temperature rises, extremes will be prevalent for both cold and heat. However, these extreme heat events are occurring more frequently with more severity, and therefore they will likely push our average temperatures higher for years to come. We've already seen average temperatures over the past decade going up."

This brutal, record-shattering heat wave follows a record-shattering winter during which a cold blast hit the southern U.S. In February, much of Texas saw its coldest air since 1989, while six states in the central U.S. ranked February 2021 among their top 10 coldest Februaries ever.

Although the connection between the cold blast and climate change is less clear, it appears that two of the most impactful weather events of 2021 were at least in part due to extremes in temperature.