As the planet has heated, hotter-than-usual spells have become more intense and now last on average about 24 hours longer than 60 years ago, according to data from the National Oceanic and Atmospheric Administration. Noaa data from the 50 most populous cities in the US shows the heatwave season is 49 days longer now compared with the 1960s.
“Extreme heat is killer heat, and multiple-day heatwaves – and early-season ones – are the biggest threat, because people can’t get a break and the body can only sustain it for so long,” said Brenda Ekwurzel, the director of climate science for the climate and energy programme at the Union of Concerned Scientists in the US. “These are not isolated heat events; this is what the turbo-charged climate change world looks like.”
In Phoenix, Arizona, the National Weather Service has issued a “very dangerous long-duration heat” alert for the second consecutive week, with daily temperatures expected to fluctuate between 29C (85F) and 47C (118F).
Temperatures in Europe are about 10-15C hotter than usual, and the heatwave is lasting a long time, as an established high-pressure system across the region is causing temperatures to climb every day. Clouds of Saharan dust are also making conditions worse.
“Unusually high sea surface temperatures are also occurring across the region, with many parts of the Mediterranean seeing surface temperatures as high as 25-28C,” said Rebekah Sherwin, a meteorologist from the Met Office’s global forecasting team. “This will exacerbate the effects of the heat over surrounding land areas, as even in coastal regions overnight temperatures are unlikely to drop much below the mid-20s celsius.”