This story was originally published by the Guardian and is reproduced here as part of the Climate Desk collaboration.

On a recent August day in the subterranean furnace of New York City’s subway, one bearded, curly haired man was studying his phone for different reasons than the other wilting passengers—to track the soaring temperatures and ponder how underground train stations can cool down in an era of climate crisis.

Jack Klein, a 31-year-old construction site manager, has in the past two years taken it upon himself to become a sort of guerrilla subway heat operative, sticking teardrop-shaped thermometers to steel beams in seven of the hottest Manhattan stations and posting social media videos of the Hades-like summer temperatures that commuters have to endure.

“This line must be cursed,” Klein said on the 4/5 line platform at 14th Street-Union Square, one of the city’s most blistering stations, as he dangled another of the monitors and saw the digits climb to 99 Fahrenheit, a good 10 degrees hotter than aboveground.

The heat index, which combines the temperature with New York’s clinging humidity, rose to 116 F, well above the level at which heatstroke can set in. “It’s been worse—I’ve seen it get to 120,” said Klein, as two nearby police officers shifted uneasily in their heavy bulletproof vests. “But this is definitely uncomfortable.”

Shortly afterward, it did indeed get worse. The monitor’s temperature reading, which displays on Klein’s phone, climbed to 101 F, with the “real feel” heat index hitting a delirious 132 F. “It’s just too hot, it’s terrible, too much,” said one Italian tourist, named Leo, on the platform.

Another passenger, a woman fanning herself, likened the heat to an oven. “I just want to get outta here,” she said. The heat’s biggest impact is upon subway staff—such as maintenance workers and cleaners—who have to toil for hours in these temperatures, a situation that their union describes as dangerous.

Most of Klein’s in situ magnetized thermometers have disappeared, either removed or fallen, but he has now switched to helping relieve the heat by heaving large dispensers of water down to platforms and agitating for better seating and proper fans. “I mean, what the hell is that even doing?” Klein grumbled about a dust-clogged overhead fan in the 14th Street-Union Square........

© Mother Jones