The Simple Truth About These Miserable Heat Waves

In order to determine whether such an event can be attributed to climate change, researchers run complex models based on historical observations: one showing the world as it is and the other “an alternative world where there isn’t any human influence on the climate,” said Nicholas Leach, a physicist at at Oxford University who researches weather and climate impacts on health. From there, scientists can determine how likely a specific extreme weather event would be in a world without climate change, i.e., with lower concentrations of human-caused greenhouse gases in the atmosphere. Other studies, Leach says, more specifically replicate the exact atmospheric patterns and conditions that produced a particular heat wave in those two worlds, observing how the intensity and severity of the resulting heat wave would change in a world where human activity isn’t causing temperatures to rise.

It’s generally easier to determine whether climate change has contributed to heat waves as compared to hurricanes, which can vary based on any number of factors in oceans and the atmosphere. “We’re warming up the atmosphere, and there’s a very strong link between doing that and the hottest possible situations getting hotter,” Leach says. “The link between climate change and thermodynamics has been understood for 100 years.”

Researchers are still working on understanding what precisely climate change is doing to the atmospheric blocks that produce heat waves, particularly in the case of extraordinary events when temperatures soar far outside the range of historical observation—like the Pacific Northwest heat wave of 2021, which caused hundreds of excess deaths across the U.S. and Canada. One study found that heat waves that extreme would “occur roughly every five to 10 years” in the same region if global temperature averages were to exceed two degrees Celsius above preindustrial times.

As Nathan Gillett—another co-author of the climate indicators study and a researcher at the Canadian Centre for Climate Modelling and Analysis—told me, the world is already experiencing heat waves that “would have been much less likely or almost impossible without human-induced climate change.” Those heat waves will worsen as humans burn more fossil fuels and continue to raze forests, which is rapidly depleting the planet’s ability to absorb carbon dioxide. The more of it that goes into the atmosphere, the hotter it gets. “There’s very high confidence,” Gillett said, “that, with ongoing greenhouse gas emissions, the world will continue to warm and heat waves will continue to be hotter. That’s going to happen everywhere.”