Global warming kills.

We're all going to die, but climate change may increase the risk of death, according to a new report by the World Health Organization (WHO). Many important diseases that affect developing countries are sensitive to climate variations, according to the report, and even a proportionally small change in the global incidence of some diseases could result in significant public health impacts far into the future.

The authors of Climate Change and Human Health: Risks and Responses quantified the relative risk of death in 2030 from diarrhea, malaria, cardiovascular disease related to heat and cold, malnutrition, and flooding in several developed and developing regions. They used a WHO-developed methodology that quantifies the disease burden in 2030 based on 26 environmental, occupational, behavioral, and lifestyle risk factors. They also consulted models that forecast climatic variations over long periods in response to likely changes in the composition of atmospheric gases. Calculating from 1990 conditions, they constructed three scenarios for estimating the relative risk of disease burden from climate change: one of unmitigated greenhouse gas emissions, a second of modest emission reductions, and a third representing more rapid emission reductions.

Africa and Southeast Asia bore much of the estimated increased disease burden. The increased risk of diarrhea was as much as 10% higher in some regions than if no climate change occurred. Large increases were estimated for malaria in regions adjacent to areas already significantly affected by the disease. Under the unmitigated emissions scenario, the western Pacific region could expect malaria to increase by as much as 83%. Temperate climates appeared to spare most of Europe from increased risk, and socioeconomic conditions protected most of the southern United States.

The greatest uncertainty in the authors' estimates stems from the lack of long-term data sets on disease rates in most regions of the world. "There are too many other influences acting over the time scale in which climate change operates," notes coauthor D.H. Campbell-Lendrum, a lecturer at the London School of Hygiene and Tropical Medicine. Still, he adds, the indication that climate change may worsen several important diseases makes it even more important to control these diseases now. "For example," he says, "provision of clean water and sanitation not only cuts overall diarrhea rates, but also decreases the importance of the bacterial pathogens that respond positively to temperature, and decreases risks of diarrhea outbreaks following floods."

The study did not include mortality estimates for many waterborne diseases affected by climate variation, broader categories of heat-related deaths, or dengue, notes Jonathan Patz, director of the Program on Health Effects of Global Environmental Change at The Johns Hopkins University. "[The report is] a great start, but I have concerns that it could be an underestimate," he says.

The authors acknowledge that their estimates are conservative. "We have left out many diseases which we would expect to be affected by climate change, usually because there are no quantitative models available," says Campbell-Lendrum. "We would expect that all diseases that show climate-associated patterns in either space or time would be affected."