Climate change is fast becoming a major public health issue. Unpredictable summer and winter temperatures last decade have been linked to an increased death rate for people 65 and up living along the northeastern coast of the U.S., according to a new Nature Climate Change study. The findings suggest that temperature swings may have a similar impact to especially sweltering summers and frigid winters. In fact, their impact may be even greater.
Multiple previous studies have linked short-term temperature changes with a rise in daily death tolls, as is the case for sudden heat waves, for example. However, there’s little evidence for the link between annual deaths and changes in seasonal temperature averages.
To investigate the effects of prolonged exposures to variable temperatures, Harvard’s Joel Schwartz and colleagues turned to data from Medicare, a national health insurance program for Americans of 65 and up. These include age, race, sex, and date of death. In order to estimate the impact of changing temperatures on mortality, the team cross-referenced information about 2,740,308 New England residents with records on local average temperature and temperature variability for different zip codes from 2000 to 2008. Nearly a third of the seniors died during the study time frame.
Living in warmer zip codes was associated with reduced mortality in both summer and winter, they found, while living in zip codes with more variable in-season weather was associated with increased mortality rates (it’s important to remember that these correlations are not direct cause-and-effect relationships.)
Additionally, milder winters did not seem to make up for severe summers. A rise of 1 degree Celsius in average summer temperatures killed 1% more people, Science reports, while that same rise in average winter temperatures saved just 0.6%.
Living in places with rapidly fluctuating temperatures makes exercising and other daily activities and behaviors more difficult. By making seasonal weather more erratic, climate change may be creating conditions that our cardiovascular and respiratory systems aren’t used to handling. “People do physically adapt,” Schwartz tells Science. “But if [temperature] bounces back and forth, we don’t.”
The team expects that people living in different climate zones will respond differently to these climate changes. As first author Liuhua Shi of Harvard tells HealthDay: "We plan to do a national study to examine the long-term effects of temperature on mortality in each climate zone."