In early July, when a former government employee accused Dick Cheney's office of deleting from congressional testimony key statements about the impact of climate change on public health, White House staff countered that the science just wasn't strong enough to include.Not two weeks later, however, things already look different. University of Texas researchers have laid out some of the most compelling science to date linking climate change with adverse public-health effects: scientists predict a steady rise in the U.S. incidence of kidney stones — a medical condition largely brought on by dehydration — as the planet continues to warm.
Kidney stones are already more common in the warmer Southern states than in the North. Urologists even talk about a "kidney stone belt," a high-risk zone through the South where populations are more likely to develop stones — crystallized chemicals (usually calcium, phosphates and oxalates from an ordinary diet) that form in the urinary tract, and often cause sharp, intense pain when they pass. The Texas researchers used regional data from the Intergovernmental Panel on Climate Change to predict how this belt might grow, publishing their report this month in the journal Proceedings of the National Academy of Sciences. By 2050, the research suggests, 56% of Americans will live in regions encompassed by the kidney stone belt, compared with 40% in 2000. And by 2095, the belt should expand to 70% of the population.
Scientists have hypothesized other health consequences of climate change before, some better supported by evidence than others: heat waves that kill, new breeding grounds for mosquitoes that spread deadly malaria or dengue fever, and stagnant warm air pockets that trap disease-causing smog. But in this study, says lead researcher Tom Brikowski, he and his colleagues are pretty sure they've traced a direct relationship between human health and temperature — no mosquitoes or air pollution are needed to make the link. Even in the belt region where kidney stones are common and populations have adjusted their lifestyles to the heat, cases still peak seasonally after periods of hot weather. A previous study found that soldiers sent to warm regions see a peak in stone risk 90 days after deployment.
What's not clear, however, is the exact relationship between temperature and kidney stone rates. If each additional degree of heat causes an incremental increase in stones, Brikowski and colleagues predict we'll see new kidney stone cases concentrated in regions with the most rapid temperature changes: California, Texas, Florida and the Eastern seaboard. But if there's a threshold temperature at which risk shoots up — some evidence suggests such a threshold exists at about 13.4 degrees C (56 degrees F) — they expect the hardest-hit regions to be those where mean temperature crosses the threshold: Northern California and the belt running from Kansas to Kentucky.
Of course, if you're in the risk zone, there are easier ways to prevent stones than by slashing greenhouse-gas emissions (though that might not be a bad idea for the heat waves and the smog). Drink plenty of fluids, and your body will be better able to dilute the relevant minerals.
Until this month, Brikowski says he'd barely thought about bigger political implications of his work. "But I did warn my family that if I get a letter from the Vice President to go hunting, they could ignore it," he says.
