Warming may spark killer heat waves

JOHNS HOPKINS (US) — Hundreds to thousands more city residents could die by the end of the century because of longer, more frequent heat waves brought on by global climate change.

From 1987 to 2005, the city of Chicago experienced 14 heat waves lasting an average of 9.2 days, which resulted in an estimated 53 deaths per year more than if there had been no heat waves.

According to a new study, published in the journal Environmental Health Perspectives, global climate change could, by 2081 to 2100, drive that average number of heat wave-related deaths to between 166 and 2,217.

“Our study looks to quantify the impact of increased heat waves on human mortality,” says lead author Roger Peng, associate professor of biostatistics at Johns Hopkins University. “For a major U.S. city like Chicago, the impact will likely be profound and potentially devastating.”

Efforts to control global warming could change the outcome, Peng says. “We would expect the impact to be less severe with mitigation efforts, including lowering CO2 emissions.”

Peng and colleagues developed three climate change scenarios, based on estimates from seven global climate change models and from mortality and air pollution data for Chicago from 1987 to 2005.

The data were limited to the warm season from May to October of each year. They adopted the definition of a heat wave used in a 2004 study from the National Center for Atmospheric Research.

The results suggest that the number of Chicago heat waves from 2081 to 2100 could multiply by a factor of anywhere from 1.1 to 31.7, while the average length of the waves could remain about the same or multiply by up to 3.9 times.

Projected length and frequency of heat waves both increased in all but one of the 21 combinations of the three scenarios and seven models.

The increased projections of excess deaths could not be explained by projected increases in city population alone. The exact change due to global warming in annual mortality projections, however, is sensitive to the choice of climate model used in analysis.

“It’s very difficult to make predictions, but given what we know now—absent any form of adaptation or mitigation—our study shows that climate change will exacerbate the health impact of heat waves across a range of plausible future scenarios,” Peng says.

Researchers from Yale University, Harvard University, and the University of British Columbia contributed to the research, which was supported by grants from the National Institute of Environmental Health Sciences and the Environmental Protection Agency.

More news from Johns Hopkins University: http://releases.jhu.edu/