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Climate change is supercharging California heat waves, and the state isn’t ready

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When a major heat wave hits Southern California, it begins with a jab — a ridge of high pressure builds over Nevada or Mexico and sweeps into the region, bringing scorching temperatures along with it.

Then comes the right hook: A mass of humid air created by unusually warm ocean water just off the northern coast of Baja California moves in from the southeast. Combined, they deliver a deadly blow, wreaking havoc on heavily populated regions such as Los Angeles County.

“We understand pretty well how and why they form,” said Glynn Hulley, a climate scientist at NASA’s Jet Propulsion Laboratory who has documented a shift toward hotter, more humid heat waves in urban areas of Southern California since 2000. “It’s almost like the heat waves have changed their personality, shifting to warmer and more humid nighttime events.”

Climate change is transforming the character of the West’s hottest periods — making them more frequent, more persistent, more humid and more lethal. Experts say this shift in heat waves should prompt changes in emergency notifications and public health response to keep the death toll from rising. But that isn’t happening.

In California and some other states, key strategies that could protect the most vulnerable and save lives, including urban cooling measures and better warning systems, remain a low priority compared with other environmental hazards such as wildfires. Environmentalists and health advocates see it as a major shortcoming in the state’s efforts to adapt to the warming climate.

“Whatever we’re doing isn’t working, and it’s only getting worse,” said Kathy Baughman McLeod, a climate resilience specialist at the Atlantic Council, a Washington think tank. Her organization formed a group of public health experts, governments and nonprofits to push authorities to begin naming and categorizing heat waves, just like hurricanes, and take other steps to better highlight the dangers.

“We’ve got to try something new and powerful to wake people up to this deadly threat,” she said.

Silhouettes of people on a cloudy sky

Santa Monica, 98° F — A group of people, seen reflected on glass panels, makes its way through muggy weather on the Santa Monica Pier in August 2021.

(Genaro Molina / Los Angeles Times)

Climatologists say there is still time to slash the buildup of greenhouse gases that is warming the planet. But even with strong action, the carbon dioxide that has accumulated in the atmosphere is projected to deliver more dire heat extremes over the next few decades.

Consider the 2006 heat wave in California. In July that year, hospitals along the California coast were overwhelmed with patients as record-high temperatures settled over the state for nearly two weeks. Bodies piled up in coroner’s offices in the Central Valley. Though state records showed that about 140 people died from the heat, researchers later estimated that there had been 650 deaths.