In late June 2021, a high-pressure atmospheric system settled over Seattle to create an inescapable heat dome. Jean-Paul Yafali, a resident of nearby Kent, Washington, thanked his good luck for the two secondhand air-conditioning units that a friend had given him back in 2019. He wasn’t used to this kind of stifling heat — not in Seattle, and not even in Kinshasa, Congo, where he grew up.

“I’m from a country where it’s really hot,” Yafali told Grist. But during Seattle’s heat dome, “it was impossible for me to last a couple minutes” outside.

By Monday the 28th, the temperature in Seattle would climb to a record-breaking 108 degrees Fahrenheit, nearly 40 degrees above normal for that time of year. National Weather Service officials warned that the pavement could reach 170 degrees in some places. Yafali and his family found respite in their AC, but they were fortunate outliers; Seattle, known for its cool, wet winters and mild summers, is one of the least air-conditioned big cities in the country. To avoid overheating, people boarded up windows with cardboard boxes. They soaked their feet in buckets of cold water and bought squirt bottles. They took refuge in shady parks or in community cooling centers.

The Pacific Northwest heat wave of 2021 was one of the most extreme ever recorded globally, a “historic, dangerous, prolonged, and unprecedented” event that took a hefty toll on people and infrastructure. Between British Columbia, Washington state, and Oregon, more than 800 people died and thousands more visited the emergency room for heat-related conditions like kidney failure and encephalopathy. Police officials in Vancouver said they spent entire 12-hour shifts going “from one sudden death to another.”

The blistering weather had many people wondering: Is this climate change?

The short answer is yes. Although the event was exceedingly abnormal — a 1-in-1,000-year event in today’s climate, according to some estimates — researchers say that without global warming it would have been at least 150 times rarer and several degrees cooler.

Indeed, heat waves around the world are happening more frequently and reaching higher temperatures because of climate change. We know this thanks to the rapidly growing field of attribution science, which allows scientists to examine the link between rising levels of atmospheric carbon dioxide and extreme weather events. When a heat wave strikes — or another disaster, for that matter, be it a hurricane, drought, or very heavy rain — attribution scientists can determine the role that climate change played in its intensification.

With extreme heat in particular, the answer is often tens or even hundreds of times more likely, thanks to a complicated mix of factors like abnormally dry soils and hotter-than-usual air. In fact, scientists are now comfortable assuming that all heat waves are being made more severe or likely because of climate change.

Read the full article about heatwaves by Joseph Winters at Grist.