Kidney stones will become more prevalent in the 21st century as the world warms up, according to Tom H. Brikowski of the University of Texas at Dallas and his colleagues. A crystallization of minerals dissolved in urine, a stone can form with the help of fluid loss. Such dehydration is more common in hotter conditions; the incidence in the southeastern U.S. is 50 percent greater than in the northwestern region of the country, for instance, and some U.S. soldiers shipped to desert conditions developed stones just 90 days after deployment. Factoring in the expected rise in mean temperature in the U.S.—upward of two to five degrees Celsius this century—the researchers figure that the nation will see 1.6 million to 2.2 million more kidney stone cases by 2050. This 7 to 10 percent increase could exact $1.3 billion in medical costs. The findings are crystallized in the July 15 Proceedings of the National Academy of Sciences USA.