The next time you feel a sharp, cramping pain in your lower abdomen, spare a thought for your personal carbon footprint.

That's the message from Dallas scientists who predict that as the planet warms during the coming century people will sweat more, not drink enough water to compensate, and therefore develop more kidney stones.

The prevalence of kidney stones may rise by 30 percent or more in some U.S. areas if global temperatures rise as forecast by the Intergovernmental Panel on Climate Change, the scientists found.

"This is really the first direct human health impact of climate change that has been demonstrated," said the study's lead author, Tom Brikowski, a University of Texas at Dallas professor of geosciences.

The study, published in Proceedings of the National Academy of Sciences, has some caveats.

It assumes the world will indeed warm, a trend contested by at least a handful of scientists. It also assumes that computer model predictions for regional warming, such as a 4-degree average temperature increase for the southeastern United States by 2050, are reliable. More scientists question the validity of such regional predictions.

Some global warming skeptics also note that the U.S. southeast has actually cooled during the last century.

"I am immediately suspicious of the assumed severe temperature change in the next decades, which is a multiple of what we have seen in the last half-century, man-made or not," said Rob Bradley, chairman of the Houston-based Institute for Energy Research.

More for you News Global warming will bring more kidney stones, study warns

However, a leading expert on global warming's impact on human health, Dr. Paul Epstein, of Harvard Medical School, called the new study "an elegant piece of work."

Epstein says that as more physicians consider the impact of global warming — doctors from the University of Texas Southwestern Medical Center collaborated on the new study — he expects more studies of this kind will highlight unknown perils of a warming world.

"We can probably expect more unexpected findings like this," said Epstein, associate director of Harvard's Center for Health and the Global Environment.

Many scientists already believe global warming will increase the reach of tropical diseases such as malaria.

Kidney stone disease occurs in about 12 percent of U.S. men and 7 percent of women. The disease is as much as 50 percent more prevalent in the Southeast than the Northwest, a difference scientists say is largely due to the fact that average temperatures in the south are about 14 degrees warmer.

Low urine volume increases the risk of kidney stones because the lower flow raises the likelihood that salt will clump together and form stones.

Scientists have found that the annual risk of kidney stone disease rises sharply when the average temperature of a location exceeds 57 degrees. The new work, therefore, suggests the highest growth in kidney stone risk will be found in middle America, from Kentucky to California, where average temperatures are forecast to rise above that threshold.

Rising temperatures would have less of an effect in a city such as Houston, where the average annual temperature is already nearly 70 degrees.

"The take-home message from this, with the caveat that you have to believe their models and that global warming will continue, is that stone disease is a big problem in the United States, and it's only going to get bigger," said Dr. Richard Link, a professor of urology at Baylor College of Medicine.

The problem could also be eased, he said, if Americans in warm climates drank about eight cups of water a day to ensure a healthy urine flow.

"The solution to this problem sounds simple, for people to monitor their fluid intake," said Brikowski, the lead author. "I know people will continue to drive their Hummers and just tell others to drink more water.

"But with global warming it's not going to be any single thing that is a crisis or will destroy society. It's kind of like living in an old house where everything slowly stops working over time. At some point you're living in a crumbling home."

eric.berger@chron.com