A PAINFUL TRUTH: GLOBAL WARMING TO INCREASE KIDNEY STONE DISEASE

An unanticipated consequence of global warming will be northward expansion of the present-day southeastern kidney stone "belt" in the U.S. Current risk of stone disease in the Southeast is up to 50% higher than for the Northwest, and this geographic variation correlates most closely with differences in mean annual temperature (MAT). The quantitative form of the relationship between MAT and stone disease incidence is uncertain; physiologically it is mediated by urine volume and therefore urinary saturation of stone-forming salts. Analysis of kidney stone incidence as indicated by Veteran's Administration office visits for urolithiasis indicates a linear 4% increase in prevalence for every 1°C increase in MAT. Published non-linear urolithiasis risk models indicate a similar trend, with slightly declining risk for MAT ≥ 17.2°C. Models of future climate consistently indicate warming, ranging over 1-6°C for this century in the U.S. Conservative warming estimates based on an average of MAT departures extracted from IPCC intermediate severity models (SRESa1b) indicates 1-2°C warming by 2050 for much of the U.S.

Future climate-related changes in urolithiasis can be predicted by combining these warming and urolithiasis temperature-dependence models. Based on the linear model, the fraction of U.S. population living in high risk zones will grow from 40% in 2000 to 50% by 2050, and to 66% by 2095. By 2050 the U.S. will experience a climate-related increase of at least 1-2 million lifetime cases of nephrolithiasis, representing a nearly 30% increase in some climate divisions. Nationwide, the cost increase associated with this rise in nephrolithiasis prevalence would approach $1 billion annually (Y2K dollars), representing a 10-20% increase over current expenditures. The spatial distribution of these increases depends on the form of the temperature-dependence model. The linear model predicts these increases will be concentrated in warm high-population states including California, Texas, Florida and the Eastern Seaboard; the non-linear model predicts concentration in a mid-latitude band stretching from Kansas to Kentucky and Northern California. A less well-defined kidney stone belt in Africa, the Mideast and South Asia will experience similar changes, with a greater impact on morbidity in developing nations.