Elfatih Eltahir looks forward to his daily stroll. He often checks the forecast first to figure out the best time to head outside.
“I find people walking, jogging, cycling and enjoying the outdoors,” said Eltahir, a professor of civil and environmental engineering at the Massachusetts Institute of Technology. “That’s what motivated me to start looking at how climate change could really constrain some of those activities.”
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He wondered, “Would we be able to do this outdoor activity in the future?” Eltahir and his co-authors set out to measure how shifting weather patterns are likely to affect the number of days when it is comfortable to be active outdoors, a metric they call “outdoor days.”
Their study, published earlier this year, found that toward the end of this century, from 2071 to 2100, the global south will likely lose a significant number of outdoor days while the global north might gain some. In a recent study published in October, the researchers found the same north-south divide will likely occur within the U.S.
This study defined an outdoor day as a day when temperatures fall within a range of 50 to 77 degrees.
Overall, the study suggested there will be minimal changes to the number of outdoor days in many states, but seasonal patterns could shift significantly. Summers, which have previously been the ideal season for enjoying the outdoors, are expected to get hotter. Meanwhile spring and fall will likely become more optimal for outdoor activities, Eltahir said.
Eltahir projects that Florida and surrounding states will suffer a 15% to 20% loss in outdoor days by the end of this century. In New England, the trend could mean a loss of outdoor days in summer, but an increase in winter, spring and fall. Northwestern states could see a 14% increase in outdoor days, the study found, driven by warmer winter temperatures.
The shift could cause changes in economic activity such as tourism. Eltahir pointed to places like Florida, where tourists are drawn to the warmer weather. With a shift in seasonal patterns, he predicted that fewer people would flock to the state in the summer, causing a smaller economic boost.
“There is anecdotal evidence that in Europe, for example, patterns of tourism during summer are already reflecting tendencies where people would prefer to spend their vacations: In the north, in places like Sweden and surrounding countries, as compared to the Mediterranean beaches in Spain and other parts of Europe.”
Eltahir and his team designed a tool that takes personal weather preferences into account when calculating outdoor days. Users can input their ideal weather conditions and navigate through different countries, including the U.S., Bangladesh and Morocco.
Kristina Dahl, vice president for science at the nonprofit advocacy group Climate Central, said the study presents a nuanced view of how climate change will affect various regions and seasons.
“I think it paints a picture of just how much life is going to change in different parts of the country in the decades to come,” said Dahl, who was not involved in the research.
Dahl has previously studied extreme heat in an effort to make climate change more tangible to the public. She said this research achieves a similar goal.
But, Dahl said, the researchers should further investigate the likely impact of climate change on outdoor days for different types of activities. Optimal temperatures for hiking are not necessarily the same as for skiing, she said.
She added that additional factors like wildfire smoke should be examined as well.
“The other thing I would mention is our ability to be comfortable outside is also matched by our ability to be comfortable inside,” said Dahl. “As we think about what it means to be exposed to more and more days with heat, we also need to be thinking about access to cooling in the home, so that if you’re exposed to heat outdoors, you’re able to cool your body down at night.”