Learning to Take the Heat: Declines in U.S. Heat-Related Mortality

Americans are learning to take the heat, literally, according to new research in this issue of EHP. Overall, the authors of the new study estimate that the risk of heat-related mortality on hotter-than-usual days was 63% lower in 2005 than it was in 1987. 1 This may indicate the U.S. population, over time, has become more resilient to temperature changes, although some cities showed greater decreases in risk than others. However, climate change could contribute to additional deaths in the future, according to lead author Jennifer Bobb of the Harvard School of Public Health. " Heat-related mortality is down, but more extreme heat exposures will lead to higher risk, " she says. " I think it is likely that we will continue to adapt, but the rate of adaptation might change moving forward from what we observed in our data from 1987 to 2005. " Bobb and colleagues projected that a 5°F increase in average daily temperatures across the United States would lead to 1,907 additional deaths each summer. (The National Climate Assessments projects average U.S. temperatures could increase by 3–15°F by 2099, depending on future emissions of greenhouse gases. 2) The researchers did not account for continued adaptation beyond 2005 in this estimate. To assess how day-today changes in temperature related to changes in daily numbers of deaths, the researchers compared daily summertime weather data for the years 1987 through 2005 with daily deaths reported in 105 U.S. cities (excluding deaths due to external causes, such as accidents and homicides). Their analysis covered about 106 million people. When they compared mortality on average-temperature days and days with higher-than-average temperatures, the researchers found that the number of excess deaths declined from 51 per 1,000 in 1987 to 19 per 1,000 in 2005. In a sensitivity analysis, they accounted for air pollution levels, which have been linked to increases in same-day mortality risks. 3 Adults over age 75 and those living in northern cities and cooler climates saw the greatest decrease in estimated heat-related mortality. Previous studies on heat-related mortality have largely assumed that mortality risk stayed constant over several years. Fewer studies have investigated how heat-related mortality risk may be changing. 6 " This study shows that the effect of temperature on deaths isn't constant over time, " says Patrick Kinney, director of Columbia University's Climate and Health Program. Kinney was not involved in the study. A number of factors …