Add kidney stones to the growing list of possible consequences of global warming. A new study warns that as many as 2.3 million more people may develop these mineral deposits in their kidneys by the year 2050 as the result of a warming world. The reason? There's a greater risk that they will be subject to dehydration in more sultry climes, which is believed to be a major contributor to stone formation, according to research published this week in Proceedings of the National Academy of Sciences USA.

"I think the reality of this study is accurate as temperatures do play a great role in stone diseases," says Stephen Nakada, chair of urology at the University of Wisconsin–Madison.

Most kidney stones form from minerals deposited in the two fist-size organs (located in the lower back on each side of the spine) as they filter urea, mineral salts, toxins and other products from the blood; others form from too much (uric) acid in the urine. Most of the sandlike crystals are tiny enough to exit the kidneys. Larger ones, however, may get stuck in the thread-like ureter that connects each kidney to the bladder, thereby blocking the flow of urine. When blockage occurs, a procedure (usually lithotripsy, which uses a surgical instrument or shock waves) is required to break it into small enough fragments to pass through the thin ureter. Urologists often suggest drinking plenty of water to help flush minerals from the kidneys to prevent stones from forming.

Researchers at the University of Texas Southwestern Medical Center at Dallas, using estimates from the International Panel on Climate Change (IPCC) of temperature swells over the next 40 years, found that the percentage of the U.S. population living in high-risk areas for kidney stones will rise from 40 percent in 2000 to 56 percent in 2050. According to their data, the greatest jump in cases will likely be in the Midwest, with an overall rise in incidence of between 10 and 11 percent.

In the U.S., about 10 percent of men and 7 percent of women will develop a kidney stone during their lifetimes. The rate has been rising in recent decades, increasing from 3.6 percent of the overall population in 1976 to 5.2 percent by the mid-'90s. The study notes that this uptick correlates with an increase of half a degree Fahrenheit (0.28 degree Celsius) during the same period.

Study co-author Yair Lotan, an assistant professor of urology, acknowledges that the study is based on estimates that may change. "This means that things may not get as bad as we predict," he says, "or it could be that there will be even more cases of kidney stones than our models tell us."