The climate change story has plenty of villains; seniors are hardly wrecking the environment on their own. Still, the demographic trends do not bode well.

“There will be more warm days in most areas because of climate change,” Dr. Estiri said. “There will be more energy use by the older group. And because of the population aging, there will be more people in that age group. These trends will amplify each other.”

But in a world that is both warming and graying, older adults suffer disproportionately from climate change.

Consider extreme heat. “It puts a stress on anybody’s body, but if you’re old and frail, it’s harder,” said Patrick Kinney, who studies the effects of climate on health at the Boston University School of Public Health. In addition, he said, “certain medications older people take, for blood pressure or cholesterol, reduce the body’s ability to thermo-regulate.”

The risk of heat stroke, which is potentially fatal, increases because older adults may be less mobile, and thus less able to reach cooler locations in a heat wave. They also may be socially isolated and less able to seek help.

With impaired cognitive function, “you might be less able to judge what to do,” Dr. Kinney said. The air pollution often associated with heat waves intensifies the problems. The Chicago heat wave of July 1995, for instance, caused 514 heat-related deaths; people older than 65 accounted for 72 percent of the fatalities.

Humans can adapt to these extremes, of course. Dr. Kinney and his colleagues found that the risk of dying from heat in New York City declined 65 percent from the early 1970s to 2006 as the proportion of households with air-conditioning surged. But air-conditioners also contribute to climate change.