We already know that heat waves can have deadly consequences -- but a new study shows that even small temperature increases -- like those linked with climate change -- can increase deaths.
Researchers from the Harvard School of Public Health found that even a 1 degree Celsius increase (1.8 degrees Fahrenheit) in temperature during the summer can increase death rates for elderly people who have a chronic health condition.
"The effect of temperature patterns on long-term mortality has not been clear to this point. We found that, independent of heat waves, high day to day variability in summer temperatures shortens life expectancy," study researcher Antonella Zanobetti, senior research scientist in the Department of Environmental Health at Harvard, said in a statement. "This variability can be harmful for susceptible people."
The study, published in the journal Proceedings of the National Academy of Sciences, included health data from 3.7 million people with chronic illness, who are over age 65, between 1985 and 2006. These people lived across the U.S. in 135 different cities.
In general, the study showed that death risk was higher in the cities that were just generally hotter. Researchers found that death rates were higher in each city when there were larger temperature swings, compared with smaller temperature swings. For example, an increase in temperature of 1 degree Celsius upped the death rate by 2.8 to 4 percent for the people in the study.
Specifically, death risk increased by 4 percent for elderly people who had diabetes and 3.8 percent for people who'd had a heart attack before. The death risk increased by 2.8 percent of those who had heart failure, and 3.7 percent for those who had a chronic lung disease condition, the researchers found.
The death risk also seemed to be 1 to 2 percent higher for African American people and for people with fewer means, while the risk was 1 to 2 percent lower for people whose cities had more green areas.
"People adapt to the usual temperature in their city. That is why we don’t expect higher mortality rates in Miami than in Minneapolis, despite the higher temperatures," study researcher Joel Schwartz, professor of environmental epidemiology at Harvard, said in the statement.
"But people do not adapt as well to increased fluctuations around the usual temperature," he added. "That finding, combined with the increasing age of the population, the increasing prevalence of chronic conditions such as diabetes, and possible increases in temperature fluctuations due to climate change, means that this public health problem is likely to grow in importance in the future."