For four out of five people on the planet, climate change made July, the globe’s hottest month on record, even hotter. And in the United States, nowhere has been more consistently hot this summer than Phoenix, which endured 31 consecutive days at 110 degrees Fahrenheit or above — the hottest month, on average, in any U.S. city on record. For 16 days, nighttime temperatures in the metropolis of 1.6 million people didn’t dip below 90 degrees, a telltale sign of climate change.

Extreme heat comes with serious public health consequences. Heat causes more deaths in America than any other weather-associated hazard. More than 11,000 people have died from heat since 1979, which is almost certainly an underestimate. Officials suspect seven people may have died due to heat in state and national parks in the Southwest this summer — an unusually high number for June and July.

In Arizona, one of the states where heat-related deaths are most common, the number of fatalities in metro-area Phoenix — 39 deaths connected to heat so far — could surpass last year’s total, potentially by a large margin. The Maricopa County Department of Public Health reported that there may have been 312 more deaths connected to heat in the county this year, all of which are under investigation.

Emergency room doctors in Phoenix are on the front lines of this challenge. This summer, physicians in Arizona have been inundated with patients suffering from heat-related illnesses, but they’ve also been seeing higher volumes of patients with chronic diseases exacerbated by heat. And burn units in the state are tending to people with severe contact burns from blazing asphalt and other hot surfaces.

All summer, Kara Geren and Frank Lovecchio, two emergency medicine physicians in Phoenix, have noticed that no matter what a patient comes in for — whether it’s chest pain or a chronic health condition such as diabetes — they also likely need fluids. “What surprised us is, even people that came in for completely unrelated things are dehydrated,” said Geren, who works at Valleywise Health Medical Center in central Phoenix. “It’s just so hard to stay hydrated.”

The patients presenting with dehydration add to the considerable number of people coming to the ER with symptoms consistent with heat-related illness: heat rashes, cramps, vomiting, diarrhea, and the most severe form of heat sickness, heat stroke.

Read the full article about extreme heat by Zoya Teirstein at Grist.