A relentless heat wave that refuses to let up brings danger to California, Southwest
For nearly a month, millions of people across the American Southwest have sizzled, sweated and sweltered under a heat wave that refuses to let up.
Day after day, residents from Fresno to Phoenix have endured triple-digit temperatures and hot, restless nights that have offered little relief.
Forecasters say the heat wave is being driven by a ridge of high pressure that has parked itself over the region, creating a pressure cooker of slowly sinking warm air.
But some experts say it is a worrisome indication of a climate that has been radically altered by human behavior colliding with the onset of El Niño.
“We would not see the kinds of temperatures globally that we’re seeing without climate change — it’s virtually impossible to explain these changes in the absence of climate change,†said Katharine Jacobs, director of the Center for Climate Adaptation Science and Solutions at the University of Arizona. “But for Arizona and the southern tier of the U.S., I think El Niño is contributing to exceptionally high temperatures at this point.â€
A ridge of high pressure continues to trap a ‘heat dome’ over Southern California, bringing risk of heat-related illness and wildfires.
El Niño is a recurring climate pattern in the tropical Pacific that is typically associated with higher global temperatures. It made its official arrival in June, and in early July the planet saw its hottest days ever recorded, with the global average shattering the previous record of 62.46 degrees four days in a row.
In the southwestern U.S., El Niño may also be resulting in a late monsoon season. That means the rain and clouds that typically move in from the Gulf of Mexico this time of year have yet to arrive and dampen the heat, Jacobs said. The high pressure associated with the heat dome may also have an added blocking feature that is preventing weather from moving as it normally does.
“We have seen a lot more of this kind of behavior since the climate change signal has been identified, where weather just doesn’t move east with the jet stream the way we expect it to,†she said.
Indeed, researchers are investigating whether human-caused climate change is altering the jet stream — fast-moving air currents that drive weather across the globe.
What is undisputed, however, is that such patterns are occurring against the backdrop of global warming caused by greenhouse gas emissions. A study published this week by World Weather Attribution found that the ongoing Southwest heat wave — as well as concurrent heat waves in Europe and China — would not have been possible without climate change.
Climate change made the European heat wave 4.5 degrees hotter, the U.S. and Mexico heat wave 3.6 degrees hotter, and the China heat wave 1.8 degrees hotter, the study found.
“Unfortunately, what we have is this moving base line where warming is very likely going to continue, and the extreme warmth that we see this decade is going to become more commonplace three decades from now,†said Daniel Cayan, a research meteorologist with the Scripps Institution of Oceanography at UC San Diego.
He said that model projections indicate that the number of heat wave days could double by 2050, and that such events will become more extreme and longer lasting.
“We’re getting a sort of flavor of that this summer, but if you’re writing this article in 2047, you’ll probably be remarking about how unusual it is compared to what it was in 2023,†he said.
Huge swaths of the U.S., including California, are expected to see warmer-than-average temperatures in August, government forecasters say.
The current heat wave has already made life miserable for millions of people.
In California’s Central Valley, temperatures have lingered at or above 100 degrees for the majority of the month, including a consecutive run of 14 triple-digit days in Fresno. Bakersfield has seen 15 days of triple-digit temperatures this July, with a 10-day streak ending Tuesday when it dropped to 99 degrees.
“We are super duper busy,†said Mary Lisa Russell, a spokesperson with the Community Regional Medical Center in Fresno. Though she could not provide the hospital’s specific intake numbers for heat-related illnesses, she said that “whenever you have heat, you have more people coming into a trauma center.â€
In Phoenix, temperatures are so high that people are suffering pavement burns from sidewalks, which are sizzling at temperatures of up to 170 degrees.
Phoenix continues to shatter record after record as the heat wave refuses to let up. The city has seen 26 consecutive days of temperatures of 110 degrees or higher — obliterating the previous record of 18 days set in 1974. Wednesday was expected to be the 27th day, said Austin Jamison, a meteorologist with the National Weather Service there.
“It’s so many days, it’s kind of blurring one into the next,†Jamison said.
But while so many hot days are cause for concern, hot nights are also dangerous.
“Heat waves are measured both in terms of intensity and duration, and I think this particular one is breaking records in both categories,†said Jacobs, of the University of Arizona. “And particularly, it’s concerning because the nighttime temperatures are so high, and that makes it very difficult for people to recover at night from all that heat during the day.â€
Unusually strong heat waves are becoming more common due to the buildup of greenhouse gases in the atmosphere, researchers say.
It has been 16 days since Phoenix saw its low temperature drop below 90 degrees. The previous record was seven days set in 2012 and 2020.
Cayan, of Scripps, said such trends are also likely to increase.
Nighttime heat waves “carry a lot of consequence because it means that households don’t cool off as much, and it means that ecosystems don’t enjoy that break,†he said. “It’s something that bears watching, and of course it has a lot of human health impacts as well as demand for energy and cooling.â€
There are other factors that may be behind July’s simmering heat, UCLA climate scientist Daniel Swain said. They include the Hunga Tonga volcano eruption of 2022, which shot record-breaking amounts of heat-trapping water vapor into the stratosphere.
During a briefing this week, Swain said that the effects of the eruption are still being studied, but that it is conceivable it may have led to temporary planetary warming.
There is some relief on the horizon, with conditions expected to be somewhat closer to normal in many parts of the Southwest beginning next week. But the relief may be short-lived, as seasonal forecasts from the National Oceanic and Atmospheric Administration indicate more heat is on the way in August.
NOAA officials also said the odds are growing that 2023 will be among Earth’s hottest years on record — if not the hottest — and that 2024 will probably be even hotter.
“The reason why this is the warmest year on record globally — and so much warmer than anything we observed in the 20th century — well, that pretty much comes down to climate change,†Swain said.
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