Environmental Factor

June 2011

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New study estimates heat wave mortality from climate change

By Melissa Kerr
June 2011

Roger Peng, Ph.D.

In several earlier studies, Peng, above, and Dominici have collaborated with NIEHS Outstanding Young Environmental Scientist (ONES) awardee(https://tools.niehs.nih.gov/portfolio/index.cfm?action=portfolio.grantdetail&grant_number=R01ES015028) Michelle Bell, Ph.D., an associate professor in the Yale University School of Forestry and Environmental Studies, who was also an author on this study. (Photo courtesy of Christopher Hartlove)

Francesca  Dominici, Ph.D.

Dominici gave a talk about her research in June 2010 at NIEHS. She is developing novel models to help solve one of the persistent mysteries of public health - the effects of environmental exposures to complex mixtures. (Photo courtesy of Steve McCaw)

Heat waves have always posed a threat to human health. With global climate change models continuing to predict rising temperatures, the specific implications of rising temperatures compounded by more frequent heat waves are a growing public health concern.

In a new study funded by NIEHS(https://tools.niehs.nih.gov/portfolio/index.cfm?action=portfolio.grantdetail&grant_number=R01ES012054) and the U.S. Environmental Protection Agency (EPA), researchers used climate change models and local historical data to predict the potential impact of warming on human mortality in the Chicago metropolitan area. One of the first efforts of its kind, the study, “Toward a Quantitative Estimate of Future Heat Wave Mortality under Global Climate Change,”(https://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.1002430) appeared in the May issue of Environmental Health Perspectives.

“Our study looks to quantify the impact of increased heat waves on human mortality. For a major U.S. city like Chicago, the impact will likely be profound and potentially devastating,” said lead author Roger Peng, Ph.D.(http://www.biostat.jhsph.edu/~rpeng/cv.html) Exit NIEHS, in a Johns Hopkins University press release. Peng is an associate professor in the Department of Biostatistics at the Bloomberg School of Public Health at Johns Hopkins University. His former colleague at Hopkins, NIEHS grantee Francesca Dominici, Ph.D.(http://www.hsph.harvard.edu/faculty/francesca-dominici/) Exit NIEHS, now a professor in the Department of Biostatistics and associate dean for information technology in the Harvard University School of Public Health, was principal investigator on the study.

Heat waves of the past

According to the researchers, heat waves have a taxing affect on the human body. Prolonged exposure to heat stresses the heart and other aspects of the human body's regulation system. If the temperature remains elevated overnight, the body becomes overwhelmed because it doesn't get the respite that it needs.

Because there is no universally accepted definition of a heat wave currently available, the researchers applied one that uses two threshold temperatures and duration as criteria. To qualify as a heat wave, they said, the high temperature must reach or exceed the 97.5th percentile of daily maximum temperatures recorded in Chicago from 1987 to 2005 for at least three days, with temperatures remaining above the 81st percentile for the entire period.

According to the researchers, Chicago was selected for the study because of its significance nationally and the frequency of heat waves there. During the 19-year period studied, there were 14 heat waves lasting an average of 9.2 days each. A total of 1,007 excess deaths, approximately 53 per year, could be attributed to heat waves.

Heat waves of the future

The research team used seven climate model simulations of temperature from the Program for Climate Model Diagnosis and Intercomparison (PCMDI) as part of the Coupled Model Intercomparison Project (CMIP3) to estimate future heat waves. The analysis examined data from the National Morbidity, Mortality, and Air Pollution Study, the National Center for Health Statistics, and the National Climatic Data Center, as well as the EPA Air Quality System, integrating historical mortality, weather, and air pollution data with climate model output.

“A key advantage of our approach is that it can be easily modified with respect to the various inputs and assumptions about the future to obtain predictions from a wide range of plausible scenarios,” the authors explained.

Based on estimates for 2081-2100, the study predicts that Chicago could expect from 166 to as many as 2,217 deaths per year from heat waves, depending on the climate change model used.

“Even in the presence of [these] large intermodel variations,” the researchers explain, “the results of our analysis suggest that annual heat wave mortality will increase in the future.”

While the researchers concede the limitations of their study, including uncertainty about future trends of human adaptation to extreme temperatures, they remain hopeful that the results of this study can be used to stimulate further research on this important topic and spur efforts to mitigate the effects of climate change.

“The impact of future heat waves on human health will likely be profound, and significant gains can be expected by lowering future carbon dioxide emissions,” they concluded.

Citation: Peng RD, Bobb JF, Tebaldi C, McDaniel L, Bell ML, Dominici F(https://www.ncbi.nlm.nih.gov/pubmed/21193384) Exit NIEHS. 2011. Toward a Quantitative Estimate of Future Heat Wave Mortality under Global Climate Change. Environ Health Perspect 119(5):701-706.

(Melissa Kerr studies chemistry at North Carolina Central University. She is currently an intern in the NIEHS Office of Communications and Public Liaison.)

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