It will be extremely dangerous. Heat waves kill more Americans, on average, than any other type of weather event. Excessive heat and humidity can damage internal organs, including the kidneys and the brain, and they can prompt heatstroke or even heart failure. And heat waves like this one—multiday episodes during which temperatures barely budge overnight—can be especially deadly, because people without air conditioning at home can’t open their windows and cool off while they sleep.

Perhaps in an earlier era, a blistering heat wave at the hottest time of the year would have seemed normal. Perhaps it would have just felt like Summer. But we know from the National Climate Assessment that human-caused climate change is making heat waves hotter, more frequent, and longer-lasting. And this heat wave in particular will help cement a very likely exceptional record: the warmest month in modern human history.

“July is shaping up to be the warmest July on record—and probably the warmest month ever measured, since July is the hottest month of the year,” Zeke Hausfather, a climate scientist at Berkeley Earth, told me. “Obviously, we still have half the month to go. But so far, it’s on track.” (Since most of the planet’s land surface is north of the equator, and since land heats up faster than the ocean, the Northern Hemisphere’s summers are the hottest months of the year for the whole planet.)

If that mark is realized, then two months in a row will be the hottest of their type ever measured, since last month was the hottest June ever recorded. And the odds are good that 2019 will be the second-warmest year on record, Hausfather told me. Either way, it’s a near-certainty that the past six years, including this one, will be the hottest six years ever measured.

And if you want to find an unusually chilly span of time, you have to go even further back. “The last time the planet had a cooler than average month, Ronald Reagan was president,” remarked the Washington Post meteorologist Andrew Freedman on Twitter yesterday.

The Bad Season means millions of people will stay inside on what could be one of the most brilliant weekends of the year. But it also means that this American scorcher comes on the heels of a record-breaking heat wave in western Europe, where France recorded temperatures above 113 degrees Fahrenheit (or 45 degrees Celsius) for the first time ever. It means summertime forest fires in California are eight times as large now as they were in the early 1970s. It means Chennai, India, a city of 10 million, is nearly out of water. It means even Arctic ice at the far north of Greenland turns to slush unnavigable by sled dogs.

This is the Bad Season. It means that a heat wave is never just a heat wave, but a symptom of a larger problem and a warning about what’s to come.

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