Temperature variability is a key factor affecting mortality associated with climate change, according to Joel Schwartz, Ph.D., from the Harvard T.H. Chan School of Public Health. Schwartz, who is also the director of the Harvard Center for Risk Analysis, discussed the challenges of studying direct effects of temperature and impacts on different populations.
His March 28 talk, “Who Will Live and Who Will Die: Temperature and Mortality in a Warming World” was part of the NIEHS Keystone Science Lecture Seminar Series.
The need for better models
Current models for studying physical responses to temperature change are not ideal, according to Schwartz. “We need to understand how the relationship between temperature and mortality changes as temperature changes,” he said.
“Temperature isn’t air pollution,” said Schwartz. “The dose-response curve really varies depending on the prevailing weather. People adapt.” Acclimatization, which is the process by which people gradually adjust to more extreme temperatures, is not addressed by most models, he pointed out.
Available temperature data also limits current models. Monitoring stations are frequently located at airports, so they may be far from where most people live and work, and may not account for the urban heat island effect. “I live in Boston,” said Schwartz. “The airport is on a peninsula sticking out into the Atlantic Ocean, where it is a lot warmer than I am in the winter, and cooler than I am in the summer.”
Furthermore, rural populations are under-studied, he said, because they live away from monitoring stations and away from the populous cities studied most frequently.
Certain populations will be especially vulnerable
Another challenge Schwartz highlighted is accounting for how temperature changes affect populations differently. Medical conditions such as Alzheimer’s disease, atrial fibrillation, or diabetes are associated with higher heat mortality. Schwartz also pointed to studies showing that socially disadvantaged populations face higher cardiovascular mortality on hot days.
Effects also vary by geographic region. Acclimatization depends on consistency, so in areas with variable temperatures people are less able to acclimate, compared to regions with consistently warmer or colder temperatures. “People adapt, but there’s probably some limit,” he said, explaining that beyond an annual summer mean temperature of about 77 degrees Fahrenheit, it appears that people do not acclimate.
For this reason, Schwartz explained, as temperatures in the U.S. increase, residents of the Northeast and Midwest may acclimate, and fewer people will die in heatwaves. However, the Southern U.S. may fare worse, with more heat-related mortality.
Key actions may help people adjust
Schwartz shared dose-response curves from studies showing that more people die during moderate heat days in cooler months than extreme heat days in summer months. “Our public health interventions for dealing with heat are focused on dealing with heatwaves, which is not where most of the deaths are,” said Schwartz. Adjusting heat warnings to account for this may reduce mortality, he suggested.
Another promising option is to increase the number of trees and the amount of green space, especially in urban areas. Schwartz pointed to data showing that such areas are associated with lower mortality, perhaps because green spaces help reduce high temperatures.
(Samantha Hall is a postbaccalaureate Cancer Research Training Award fellow in the National Cancer Institute Center for Cancer Research Laboratory of Toxicology and Toxicokinetics.)