If you've ever had a kidney stone, you know that the pain is excruciating. If you haven't yet, your chances are getting better all the time—thanks to global warming.
"Once you've had one, you will make all your efforts to not get another," Ketan Badani, a urologist at Mount Sinai hospital in New York City, told me. The solidified mass of calcium must travel from your kidney down a narrow tube called a ureter to your bladder.
This process could take a few days or a few hours, but the pain is often compared to being in labor: it comes in contraction-like waves, centered below your rib cage on your back, and it can't be ameliorated by changing position. The nausea is crippling and often induces vomiting. If the stone is smaller than five millimeters, you can probably pass it. If not, after a few days of pain, you'll have to get it surgically removed.
Lots of factors determine whether you will get a kidney stone, such as your diet and the speed of your metabolism. One surprising factor is where you live. The medical community refers to the south and southwest as the "kidney stone belt," and it's no joke—in 2000, it was home to over 40 percent of the Americans who were up to twice as likely to have kidney stone disease than those in the west or east.
One 2008 paper has predicted that rising temperatures will expand the kidney stone belt, putting 70 percent of the population at a higher risk by the end of the century.
I see what they're like, and I try my hardest to not to get them.
So far, the circumstantial evidence supports this theory; the number of people who get kidney stones has doubled in the past two decades, and the top ten hottest years on record fell within the same period. And even though the correlation may be unexpected, another recent study focused on kidney stones' prevalence in children came to the same conclusion.
The location of the kidney stone belt isn't a coincidence; people in hot places tend to spend more time dehydrated. "The most common cause of kidney stones worldwide is dehydration, and usually that's because of heat," Badani said. In hot places, you need more water just to go about your daily business, and people often forget to replenish their fluids, which means the calcium in their bodies is less diluted (most kidney stones are comprised of crystalized calcium oxalate). But the stones take a while to take shape.
"After a climactic event happens, you usually see all the stones forming two or three months later," Badani said. Right now, urologists like Badani see the most kidney stone patients in October and November, after the summer heat has largely subsided. "But if you're constantly in a hot environment, like Texas or California, there may not be as much of a seasonal variation," he added. This means that the average cost of care, the paper's authors wrote, will increase drastically—bad news for an already beleaguered health care system.
The 2008 paper used climate prediction models to anticipate where people's risk for kidney stones will increase the most:
The areas with the greatest risk by 2050 are places that aren't currently part of the kidney stone belt, but where the temperature is rising fastest. This is mostly in the Midwest, where there are no nearby oceans to moderate the temperature increase. Based on population distribution from 2000, this would mean that over 50 percent of the US population would be inside the belt by 2050. Meanwhile, heat waves and droughts like the one afflicting California this summer are expected to become more common, increasing the risk of kidney stones further.
Of course, increasingly limited access to water doesn't necessarily mean that people are drinking less of it.
"Even if there's a higher temperature at a certain time of year, as long as you stay hydrated you'll minimize your risk," Badani said. Plants may not get watered as much, he continued, but people are going to find a way to keep drinking water. However, they do have to be more careful and conscious of not getting dehydrated, and heat exhaustion can have many other, more lasting effects than a painful (but ephemeral) kidney stone.