Summer heat is about to go from bad to worse, as multiple regions around the world face another round of record-breaking temperatures.
The heat will be fueled by unusually hot ocean waters and El Niño as well as changes to the jet stream that lock high temperatures in place—and man-made climate change, of course.
Western Europe endured its hottest June on record and record-breaking wildfires in July. Now, it’s facing another round of blistering temperatures. On Tuesday, French president Emanuel Macron said the one-two punch of high heat and intense wildfires are creating a dangerous situation, which he called “the toughest since the Second World War.” Hundreds of heat records are falling across other parts of Europe, from Spain to Germany.
The western US is also bracing for high heat from the California coast to the Rockies this weekend. Temperatures in Phoenix are expected to reach up to 115 degrees Fahrenheit (46 degrees Celsius), while Salt Lake City could see a record-breaking high of 106 Fahrenheit. Montana is also under an extreme heat watch, with parts of the state expected to see temperatures as high as 110 Fahrenheit. The hot and dry conditions have the potential to supercharge some of the fires already burning across that state.
“All of these interior Western cities will be at our near record temperatures for early August, which is saying something—it’s a pretty hot time of the year to begin with, so it’s a fairly high bar,” says Daniel Swain, a climate scientist at the University of California Agriculture and Natural Resources. Overnight temperatures in some of these places are forecast to be unusually high. In Phoenix, “temperatures won’t drop much below 100 degrees,” Swain says. “That’s extremely, extremely hot, even for a place that is infamous for being very hot.” (The city tied the record for its highest low temperature last Thursday, with temperatures bottoming out at 97 degrees Fahrenheit.)
Parts of Asia are also dealing with searing heat, including South Korea and Japan. In short, large swaths of the weather map have been painted red.
The sweltering temperatures are being driven in part by a series of heat domes, or areas of high pressure that lock in sunny skies and warmth. The reason so many areas of high pressure are locked in place is due to the shape of the jet stream. The band of air that blows from west to east around the northern hemisphere “creates and steers most of the weather we experience,” says Jennifer Francis, a senior scientist at the Woodwell Climate Research Center.
When the jet stream becomes wavy, that can allow tropical air to push northward and get locked in place over areas that are usually more temperate. In Europe’s case, the jet stream is bringing extra heat from abnormally warm ocean waters around the continent.
“The seas all around Europe are running a fever,” Francis says. “These feverish ocean temperatures are directly linked to the extra heat-trapping carbon pollution we’ve been dumping into the atmosphere for decades. About 90 percent of that trapped heat goes into the ocean, and we’re feeling the consequences this summer.” Francis also points out that the oceans around Japan and China are also unusually warm, helping to fuel the heat waves there.
A recent analysis found that the heat wave that hit Europe in June and left more than 1,000 people dead would not have been possible without the extra heat that burning fossil fuels has added to the atmosphere.
Regional weather is also playing a role. The western US heat wave is due in part to downwind effects of Hurricane Genevieve, a Category 5 hurricane that built up over warm ocean waters off the coast of Mexico this week. The storm is essentially shooting a pulse of heat and energy into the atmosphere. (If you want to go deep, Swain gets into the complex mechanics on his blog.)