It can be difficult to connect a certain amount of average global warming to everyday experience, so MIT researchers have devised a different approach to quantifying the direct impact of climate change. Instead of focusing on global averages, they came up with the concept of “outdoor days”: the number of days per year in a given location when the temperature is not too hot or cold to enjoy normal outdoor activities. , such as going for a walk, playing sports, gardening, or dining outdoors.
In a study published earlier this year, researchers applied this method to compare the impact of global climate change in different countries around the world, showing that much of the global south would suffer significant losses in the number of days outdoors, while Some northern countries could see a slight increase. Now, they’ve applied the same approach to compare results from different parts of the United States, dividing the country into nine climate regions and finding similar results: Some states, especially Florida and other parts of the Southeast, should see a significant drop. on outdoor days, while some, especially in the Northwest, should see a slight increase.
The researchers also looked at correlations between economic activity, such as tourism trends, and changing climate conditions, and examined how the number of days outdoors could lead to significant social and economic impacts. Florida’s economy, for example, depends largely on tourism and people who travel there for its pleasant climate; A significant drop in days when it is comfortable to spend time outdoors could make the state less attractive.
The new findings were published this month in the journal. Geophysical research lettersin a paper by researchers Yeon-Woo Choi and Muhammad Khalifa and civil and environmental engineering professor Elfatih Eltahir.
“This is something very new in our attempt to understand the impacts of climate change, in addition to extreme changes,” says Choi. It allows people to see how these global changes can affect them on a very personal level, rather than focusing on global temperature changes or extreme events like powerful hurricanes or an increase in wildfires. “To my knowledge, no one else takes this same approach” to quantifying the local impacts of climate change, he says. “I hope many others will follow our approach to better understand how climate can affect our daily lives.”
The study looked at two different climate scenarios: one in which maximum efforts are made to curb global greenhouse gas emissions and a “worst-case” scenario in which little is done and global warming continues to accelerate. They used these two scenarios with all available global climate models, 32 in total, and the results were broadly consistent across all 32 models.
Reality may be somewhere in between the two modeled extremes, Eltahir suggests. “I don’t think we’re going to act as aggressively” as the low-emissions scenarios suggest, he says, “and we may not be as careless” as the high-emissions scenario. “Maybe reality will emerge in the middle of the century, towards the end of the century,” he says.
The team looked at the difference in temperatures and other conditions over several ranges of decades. The data already showed some slight differences in outdoor days from the 1961-1990 period compared to the 1991-2020 period. The researchers then compared these most recent 30 years to the last 30 years of this century, as projected by the models, and found much larger differences in the future for some regions. The strongest effects of the model were observed in the southeastern states. “It appears that climate change is going to have a significant impact in the Southeast in terms of reducing the number of days outdoors,” says Eltahir, “with implications for the quality of life of the population, and also for the attractiveness of tourism and for people who want to retire there.”
He adds that “surprisingly, one of the regions that would benefit a little is the Northwest.” But the gain there is modest: About a 14 percent increase in days outdoors is projected for the last three decades of this century, compared with the period from 1976 to 2005. By comparison, the American Southwest faces an average loss of 23 percent of its days outdoors.
The study also delves into the relationship between climate and economic activity by looking at tourism trends from US National Park Service visitation data and how they align with differences in climate conditions. “By taking into account seasonal variations, we found a clear connection between the number of days outdoors and the number of tourist visits in the United States,” says Choi.
According to the study, in much of the country there will be little overall change in the total number of annual days outdoors, but the seasonal pattern of those days could change significantly. While most of the country now has the most days outdoors in the summer, that will change as summers get hotter, with spring and fall becoming the preferred seasons for outdoor activity. .
In a way, Eltahir says, “what we’re talking about will happen in the future.” [for most of the country] It’s already happening in Florida.” There, he says, “the really nice time of year is spring and fall, and summer is not the best time of year.”
People’s comfort level with temperatures varies somewhat between individuals and between regions, so researchers designed a tool, now freely available online, that allows people to set their own definitions of the lowest and highest temperatures. highs they consider suitable for outdoor activities, and then see what the climate models predict would be the change in the number of days outdoors for their location, using their own comfort standards. For their study, they used a widely accepted range of 10 degrees Celsius (50 degrees Fahrenheit) to 25 C (77 F), which is the “thermoneutral zone” in which the human body requires neither metabolic heat generation nor evaporative cooling to maintain your core temperature; In other words, in that range there is generally no need to shake or sweat.
The model focuses primarily on temperature, but also allows people to include humidity or precipitation in their definition of what constitutes a comfortable day outdoors. The model could be expanded to incorporate other variables such as air quality, but the researchers say temperature tends to be the main determinant of comfort for most people.
Using their software tool, “if you don’t agree with how we define an outdoor day, you can define one yourself and then you’ll see what the impacts are on the number of outdoor days and their seasonality,” Eltahir says.
This work was inspired by the realization, he says, that “people’s understanding of climate change is based on the assumption that climate change is something that is going to happen at some point in the future and that it is going to happen to them.” to someone else. It’s not going to affect them. directly. And I think that contributes to the fact that we’re not doing enough.”
Instead, the concept of days outdoors “brings the concept of climate change home, brings it to everyday personal activities,” he says. “I hope people find it useful in bridging that gap and providing a better understanding and appreciation of the problem. And I hope that helps drive strong science-based policies around climate change.”