Scientists have studied how the number of ‘outdoor days,’ or days with comfortable weather for outdoor activities, will change across different regions in the U.S. as the climate warms. The Southeast is expected to see a considerable decline in these outdoor days, while the Northwest may enjoy a slight increase.
Understanding how global warming affects daily life can be challenging. That’s why researchers from MIT have created a new way to evaluate the immediate effects of climate change. Instead of looking at global averages, they introduced the idea of “outdoor days.” This term refers to the number of days in a year where people can enjoy normal outdoor activities—like taking walks, playing sports, gardening, or dining outside—because the temperatures are just right.
In their recent study, the researchers applied this concept globally, discovering that many regions in the global south would face significant reductions in outdoor days, while some countries in the north might see a slight increase. Now, they’ve taken the same concept and examined its effects in various U.S. regions, dividing the nation into nine climate zones. Their findings echoed the global results: Florida and other southeastern states are likely to experience a notable decrease in outdoor days, whereas some areas in the Northwest could witness a minor rise.
The team also explored the connections between economic activities—like tourism—and changing climate conditions, investigating how shifts in outdoor days could have meaningful social and economic impacts. For instance, Florida’s economy heavily relies on tourism and attracting new residents for its pleasant climate; a significant reduction in days suitable for outdoor enjoyment could diminish Florida’s attractiveness.
This research was recently published in the journal Geophysical Research Letters, co-authored by Yeon-Woo Choi, Muhammad Khalifa, and Elfatih Eltahir, a professor of civil and environmental engineering.
“This approach provides a fresh perspective on understanding climate change impacts, alongside changing weather extremes,” Choi explains. It allows individuals to grasp how global changes might directly affect their daily lives, instead of solely focusing on global temperature shifts or extreme weather events like hurricanes or wildfires. “As far as I know, no one else quantifies the local impacts of climate change in this manner,” he adds. “I hope more people will adopt our approach to better comprehend how climate might influence our everyday experiences.”
The study examined two climate scenarios: one where significant efforts are made to reduce greenhouse gas emissions, and another ‘worst-case’ scenario where emissions continue to rise unchecked. They analyzed these scenarios using all available climate models—32 in total—and found consistent results across all of them.
According to Eltahir, the true outcome might fall somewhere between these two modeled extremes. “I don’t believe we will be as proactive as the low-emission scenario suggests,” he notes, “nor will we be as negligent as the high-emission scenario implies. The reality may land in the middle by the century’s end,” he continues.
The researchers compared temperature variations over several decades. Their data indicated some changes in outdoor days between 1961-1990 and 1991-2020. By comparing the last 30 years of this century—which the models project—against the previous three decades, they found even larger disparities for certain regions. The modeling showed the Southeastern states would feel the most significant reduction in outdoor days. “Climate change will significantly impact the Southeast by reducing outdoor days, affecting both residents’ quality of life and the area’s tourist appeal,” Eltahir explains.
Interestingly, they found that the Northwest might experience slight benefits, with a predicted increase of about 14 percent in outdoor days for the last 30 years of this century compared to the 1976-2005 period. In contrast, the Southwest is expected to face an average loss of about 23 percent of their outdoor days.
The study also explored the link between climate and economic activity by examining tourism trends based on visitation data from U.S. National Parks. They found a clear relationship between outdoor days and annual tourist visits. “Taking seasonal changes into account, we see a strong association between the number of outdoor days and tourist interest in the U.S.,” says Choi.
Overall, the study revealed that most regions would see little change in the total number of outdoor days annually. However, the distribution of these days might shift significantly with summers becoming hotter, leading to spring and fall becoming the preferred times for outdoor activities.
As Eltahir pointed out, “what’s anticipated for the future [in most of the country] is already happening in Florida.” He observes that “spring and fall are the most enjoyable seasons, while summer isn’t ideal.”
People’s comfort levels with temperature can vary widely, so the research team created a freely accessible online tool that enables individuals to define their own temperature preferences for outdoor activities. Users can see projected changes in outdoor days for their area based on their own comfort thresholds. For this study, they used a commonly accepted comfortable temperature range of 10 degrees Celsius (50 degrees Fahrenheit) to 25 C (77 F), which is termed the “thermoneutral zone,” where the human body does not need to exert energy to regulate temperature.
This model primarily focuses on temperature but also allows users to incorporate factors like humidity and precipitation into their outdoor day definitions. While air quality can affect comfort, the researchers believe that temperature is the most crucial factor for many people.
The software serves a dual purpose: if users disagree with the established definition of an outdoor day, they can create their own and examine how that affects the number and seasonality of their outdoor days,” explains Eltahir.
The inspiration for this research came from the realization that “many people’s understanding of climate change is based on the notion that it’s a distant issue that won’t impact them directly. This view can contribute to inaction,” he says.
By framing the issue of outdoor days, the concept aims to bring climate change home and relate it to daily activities, Eltahir concludes. “I hope that this helps bridge the gap in understanding, fostering a deeper appreciation for the problem, and ultimately leading to science-based policies regarding climate change.”
