Death Valley on Thursday scorched in 40C, while the often cool and foggy San Francisco tied its historic March record at 29C and skiers in Colorado were hitting the slopes shirtless.
The National Weather Service issued extreme heat warnings on Friday for much of the southwest, ranging from Los Angeles and coastal southern California to the desert gambling capital of Las Vegas.
Warnings were also issued against leaving children or pets in cars.
The phenomenal heat when winter is only just ending alarmed climate watchers.
“This heatwave would be virtually impossible for the time of year in a world without human-induced climate change,” the World Weather Attribution network of climate scientists said in a report.
They described the event as being so rare that despite overall rising temperatures, something this serious is only “expected to occur about once every 500 years”.
“These findings leave no room for doubt. Climate change is pushing weather into extremes that would have been unthinkable in a pre-industrial world,” said one of the study’s authors, Friederike Otto, a professor at Imperial College London.
“In the US west, the seasons that people and nature were used to for centuries are disappearing, putting many, including outdoor workers and those without air-conditioning, in danger,” she said.
“The threat isn’t distant – it is here, it is worsening, and our policy must catch up with reality.”
‘This is global warming’
Scientists say there is overwhelming evidence that today’s heatwaves are a clear marker of global warming, a process driven chiefly by the burning of fossil fuels.
With the Northern Hemisphere officially exiting winter on Friday – the first day of astronomical spring – the soaring temperatures were wreaking havoc on wildlife in the west.
Many plants and trees are already blooming, and vegetation is growing at a fantastic clip, fuelled by heavy rains in December and January.
Terry Salas, who was out and about in Los Angeles on Thursday, told AFP the climate across the United States in recent weeks had been crazy.
“This is very unusual. We’re still in winter,” she said. “But this is global warming. The East Coast is just tornadoes and snow, and here we are, we’re sizzling.
“We’re having summer temperatures that we never, ever had in March.”
– Agence France-Presse