Scientists predict that global climate change will generate more heat waves in the decades ahead, but few studies have quantified the negative health effects of heat waves. In a new study that looked at how heat waves may impact people living in a major U.S. city, researchers at Harvard School of Public Health (HSPH) and Johns Hopkins Bloomberg School of Public Health estimate that the city of Chicago, Ill., could have 166 to 2,217 additional deaths annually due to heat waves in the years 2081–2100.The study, based on three different climate change scenarios, was published in the May 2011 issue of Environmental Health Perspectives. “Our results show that for a major U.S. city, the impact of future heat waves on human health will likely be profound,” said senior author Francesca Dominici, professor of biostatistics and associate dean for information technology at HSPH, who conducted the research at both Johns Hopkins and HSPH. The study results are an incentive for the public to take steps now to reduce future carbon dioxide emissions to help reduce the risk of climate change and severe weather, she and her colleagues wrote.According to the American Red Cross, heat waves – or prolonged periods of heat about 10 degrees above a region’s usual high temperature during the summer and often accompanied with high humidity – have caused more deaths than all other weather events, including floods. In 1995, for instance, Chicago experienced a severe summer heat wave that caused nearly 700 excess deaths in the city in one week.In the new study, Dominici and her colleagues used 1987-2005 data on mortality and air pollution in Chicago collected in the National Morbidity, Mortality, and Air Pollution Study, along with various climate models, to predict the future excess mortality from heat waves for the years 2081 to 2100. The researchers tracked nonaccidental deaths from May to October each year of the study and paired this data with levels of particulate matter and ozone, temperature, and dew point temperature for the city.The researchers found Chicago had 14 heat waves from 1987 to 2005 that lasted an average of nine days, resulting in about 53 excess deaths annually. The projected excess deaths cannot be explained by population increases, the researchers report.