Earlier this year, over 2,000 people died in India—and over 800 in Pakistan—as a result of an intense and unrelenting heat wave, where for months temperatures consistently hovered well above 100 degrees Fahrenheit, leaving melted pavement in their wake. While scientists have hesitated to directly link this heat wave to climate change, there is a strong consensus that as the effects of global warming become more pronounced, extreme summer seasons will, in turn, become more lethal. The assumed silver lining, though—if it can be called that—is the commonly held assumption that this increase in heat-related deaths would lead to a resulting decrease in winter-related deaths, as the usually cold months become less intense. A group of international researchers, however, have challenged that notion, showing that temperature alone doesn't have a major effect on seasonal mortality rates.
Previous studies on seasonal deaths have, the authors claim, done a poor job at separating the related but distinct factors of temperature effects (cold) and seasonal effects (more time spent inside, lack of exercise). This latest study thus sought to explore the singular issue of temperature effects. "If cold is responsible for a substantial fraction of winter mortality, then future warming would be expected to lead to substantial reductions in winter mortality," the researchers, led by Columbia University's Patrick Kinney, write in Environmental Research Letters. "However, if seasonal factors other than temperature are mainly responsible for winter excess mortality, then climate warming might have little benefit."
"Among 39 cities in the US and France, there was no evidence that cities that have acclimatized to warm temperatures experience any less winter mortality than do cooler cities."
With that question in mind, the researchers looked at 39 cities with varying climates in France and the United States, controlling for the effects of seasonality, such as storms, snowfall, and ice. What they found was that cold temperatures do not, in fact, drive excess mortalities in winter. "Among 39 cities in the US and France, there was no evidence that cities that have acclimatized to warm temperatures experience any less winter mortality than do cooler cities," the researchers write.
So what exactly does this mean? Well, it stands in direct contrast to the previous notion that future global warming would decrease temperature-caused winter deaths, and points toward seasonal factors other than temperature as the main culprit for excess winter mortality. These seasonal factors, the authors suggest, could include "lack of exercise, time spent indoors, school schedules, holiday gatherings, and air moisture content, [which] may lead to increased risks of respiratory infections during winter months." That last point—the lack of humidity—might play a very large role in winter-related deaths: Dry air increases the risk of influenza, and has been linked to cardiac arrhythmias in adults.
As the effects of climate change become increasingly pronounced, it's more important than ever to understand future mortality impacts, the authors note, for both economic assessments and adaptation planning.
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