Expect more record-shattering heat waves like the one that hit the Pacific Northwest recently

The recent deadly heat wave in the Pacific Northwest, during which all-time temperature records were shattered by several degrees, is a prologue to what is coming across much of the U.S., Europe and Asia, a new study finds.

Why it matters: The study shows that the rate of climate change is an under-appreciated driver of extreme heat, and that today’s quickening pace of warming virtually guarantees more extreme temperature records in coming decades.

1. The study, published Monday in Nature Climate Change, also finds that looking to past extreme temperatures when making infrastructure decisions offers a poor guide to the future given how quickly human-caused greenhouse gas emissions are transforming the likelihood of unprecedented heat extremes.

Details: The study shows that the rate of warming, rather than the absolute amount of warming compared to preindustrial levels, is an important determining factor in how likely it is that heat waves will greatly exceed temperatures previously observed in a particular location.

What they did: Using computer models and records of past weather events, Erich Fischer and his colleagues at ETH Zurich examined how the chances for record-shattering heat waves have been shifting and will continue to change as global warming continues.

1. They focused on the occurrence of week-long, record-shattering heat waves, such as the one that recently occurred in the Pacific Northwest and Canada, and examined how these probabilities would change depending on the rate and amount of greenhouse gas emissions.

By the numbers: During the Pacific Northwest’s deadly heat wave, Seattle hit an all-time high of 108°F, while Portland shattered its old record to reach 116°F. The previous record in Portland was just 107°F, whereas Seattle had only seen the mercury rise to 103°F prior to this event.

1. Typically, all-time temperature records are exceeded by fractions of a degree.

2. The study found that under a high emissions scenario, record-shattering heat extremes (at least three standard deviations from average) are two to seven times more likely during the 2021–2050 period, and three to 21 times more likely during the 2051–2080 period.

3. The greatest frequency of these heat extremes would occur during periods of faster warming immediately following years of relatively flat temperature growth.

4. The planet is currently warming at a rate of about 0.18°C, or 0.32°F per decade, according to NOAA. This is considerably faster than the warming rate during the previous 40 years, which puts us at greater risk of unprecedented heat.

What they’re saying: “The main message is that we need to prepare for more record heat events in the coming decades that shatter previous record temperatures by large margins,” Fischer told Axios via email.

1. “Because the probability of record-shattering events is directly related to the speed of warming, this is yet another piece of the puzzle that demonstrates that in order to reduce the risk of such record-shattering heat, greenhouse gas emissions need to be reduced very rapidly,” Fischer said.

Outside experts who were not part of the new study told Axios the research helps explain what’s being seen in the real world.

1. “All I can say is, wow, what a remarkably prescient paper,” said Daniel Swain, a climate scientist at UCLA, noting that it was completed and submitted for publication prior to the heat waves this summer.

2. “The notion that events we assumed were vanishingly rare or impossible, due to our relatively limited historical record, are probably not nearly so rare in the real world,” Swain added, noting that in the case of the Pacific Northwest heat event, unusual but not unheard of weather patterns were able to produce astonishing temperature records.

3. “We don’t need to invoke some kind of exotic new mechanism for so-called ‘black swan’ heat waves,” he said. “All it takes is to get unlucky with a confluence of the same ingredients that produced lesser historical heat waves.”

4. Friederike Otto, who helps lead the global effort to analyze climate change’s role in producing extreme weather events, said the paper shows that even very rare events like the Pacific Northwest heat wave are “increasing rapidly in likelihood with still increasing warming rates.”

5. On the other hand, Michael Mann of Penn State University told Axios that model shortcomings regarding the physics of extreme events and atmospheric circulation means that the new study’s projections are quite uncertain.

What’s next: Even if world leaders decide to slash greenhouse gas emissions in the near term to avoid potentially devastating amounts of global warming, unprecedented heat extremes will still grow more common and damaging during the next several decades due to the lag time that the planet’s climate has built into it.

Go deeper: In summer of apocalyptic weather, concerns emerge over climate science blind spot

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