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Silver Lining? Climate Change Could Make Americans More Fit
Credit: Beach exercise photo via Shutterstock

Even the biggest fitness fanatics have at some point checked the day's weather and then opted against a daily run. As the planet warms, that will happen less frequently, at least in the United States, a new study said.

Researchers in the new study looked at information on people's physical activity along with historical weather data, making note of associations between weather and overall exercise levels. The scientists then applied those patterns to predictions for the future climate in the U.S. They concluded that although more days of extreme heat will discourage exercise, this will be overshadowed by the boost in American's physical activity levels that will come with the increase in warm days.  

The findings mean that even though global warming is predicted to unleash flooding, frequent typhoons, economic hardship and global conflicts, Americans may at least get more exercise as the planet warms, according to the study, published today (April 24) in the journal Nature Human Behavior.

"We have uncovered a climate effect — a small, tiny, little silver lining — that is dwarfed, by comparison, to some of the other climate impacts that we're identifying in this field," said study lead author Nick Obradovich, a postdoctoral fellow in the Science, Technology and Public Policy program at Harvard University's John F. Kennedy School of Government. "There is a robust link between higher temperatures and increased physical activity in the United States." [5 Ways Climate Change Will Affect Your Health]

In the study, Obradovich and his colleagues used data on reported physical activity levels from over 1.9 million Americans collected between 2002 and 2012 by the Centers for Disease Control and Prevention. The researchers overlayed those reports with daily weather data and found that very cold and very hot temperatures, as well as rain, corresponded to a decrease in physical activity.

Among those factors, cold weather was the most significant deterrent, the researchers found.

"One of the main ways Americans engage in physical activity is by going outside and going for a walk, spending time in the park and things like that," Obradovich told Live Science. "It makes sense that when it's warmer out, people are more likely to go outside."

Obradovich then combined the historical data linking exercise to weather with data sets from NASA Earth Exchange (NEX). These data sets collate historical records and climate models to produce high-resolution forecasts for the end of the century. The modeling showed that as temperatures warm, overall exercise rates are expected to rise across the United States, particularly during winter months, the study said.

It was, in fact, the opposite of what Obradovich had predicted before he set about crunching data, he said. The idea to do the study struck him as he labored through an afternoon run in nearly 100-degree Fahrenheit (38 degrees Celsius) heat in San Diego one day last October, he said.

"The heat wave really messed up my running routine," he said. "So my initial layman's intuition was that as it gets hotter outside, people will be less inclined to do their exercise."

Since southern states already experience higher temperatures than the rest of the country, Obradovich broke out how a projected increase in temperature might affect different parts of the country. The analysis showed that while most of the country would be expected to show a net increase in physical activity, southern states would see a slight net decline. Hotter weather was most likely to discourage the elderly and the obese from being physically active, according to the study. [Map Shows How Climate Change Will Affect Health Across US]

Overall, however, Obradovich said the data linking a decrease in physical activity with hot weather was "less statistically significant" than the data linking an increase in physical activity with warmer weather.

Part of the reason, he said, could be that even in hot weather, most Americans can get out in the early morning before temperatures become unbearable and then retreat for the rest of the day in their air-conditioned homes and offices.

The results, Obradovich emphasized, are limited and apply only to the United States. People living in poorer countries with hotter climates, such as in sub-Sahara Africa, he said, would not be predicted to fare so well.

"Really hot temperatures in those countries will cause heat stress and could impact not only exercise, but also occupational activities," he said. "Plus, in these poorer nations, getting water and food is much more of a priority than exercise."

"The litany of effects of climate change is overwhelmingly negative and quite scary, frankly," he said. "But when you look at all the possible complex human behaviors and how they're affected by climate change, occasionally you see something that is slightly positive."

Originally published on Live Science.