The US hasn’t seen anything quite like this. Over the weekend, temperatures soared to new triple-digit heights across the American West. The immediate cause was a “heat dome,” a mass of high-pressure air trapping heat beneath it, one far stronger and larger than normal.
But what we saw this weekend is what climate scientists have been predicting for decades. And it’s a taste of what’s to come. “It’s surreal to see your models become real life,” Katharine Hayhoe, climate scientist and chief scientist at the Nature Conservancy, says in the Guardian.
Records fell across the region. On June 17, California’s capital of Sacramento hit 110°F (43°C), smashing the last record of 102°F set in 1976. Similar all-time highs fell in Las Vegas, Denver, Phoenix, and other cities thousands of miles apart. In Death Valley National Park, where temperatures soared to 128°F, just one degree off the record, nighttime temperatures stayed above 111°F (44°C) well past midnight, among the hottest nights ever recorded in North America.
It’s hard to argue with climate models
What climate models predicted is coming true. Scientists forecast global warming would fuel higher temperatures, falling humidity, dwindling snowpack, and intensifying drought. So far, this is coming to pass, despite some uncertainty about how this will play out in the coming century.
Extreme heatwaves are now an estimated 3 to 5 degrees Fahrenheit warmer across the US, estimates Michael Wehner, a senior scientist at Lawrence Berkeley National Laboratory. In the West, the hottest days have gotten about 33% drier in Nevada and California over the last 40 years, according to the University of California, Los Angeles (UCLA) climate scientist Karen McKinnon. A “megadrought” now engulfing the region is eclipsing any period for the last 1,200 years.
Little of this is surprising for scientists who run supercomputers modeling the planet’s atmosphere. In 2019, climate scientist Zeke Hausfather analyzed 17 climate models run between 1970 and 2007 and found more than half predicted outcomes “indistinguishable from what actually occurred.” More than 80% correctly analyzed how the atmosphere would respond to rising greenhouse gases level after controlling for models that overestimated humans’ GHG emissions.
When will the heatwave be over?
The West’s drought appears to be without precedent in recorded history. From Oregon to the Mexican border, drought intensity has reached “exceptional” levels. Decades of low rainfall, and two especially dry years, have turned the region into a tinderbox with 100 million dead trees in California alone, and millions more ready to burn. With the hottest, and driest, period of the year still ahead, conditions are “as bad as they can be,” says Daniel Swain, a climate scientist at UCLA.
Last year, similar (but not as dry) conditions led to an apocalyptic fire season that killed 33, burned 4% of the state (4.4 million acres), and left the entire coast languishing under blood-red skies. Fires are breaking out again in California more than a month early. Ranchers and farmers are starting to talk about shrinking their herds, or ending their livelihoods, as the wells dry up: 20% of California’s prime farmland in the San Joaquin Valley has been fallowed.
On the surface, water is vanishing as well. For the first time, the massive reservoir behind the Hoover Dam, Lake Mead, registered just 37% full. That’s threatening power and water supplies for seven states (Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming) in the Colorado River basin (the dam’s generation is already down 25%). In California, the loss of snowpack means that power generation is forecast to drop 70% below the 10-year average, while some power-producing dams, such as the one on Lake Oroville, could stop generating power for the first time since they were built more than 50 years ago.
This week’s misery won’t go on forever, and some relief is in sight for the West this week. Temperatures will ease as the heat dome begins to dissipate over the Southwest. But a new heatwave is already gaining steam, this time in northern California and up along the Pacific coast. “Additional records may be set, once again,” writes Swain.