Credit: National Recreation and Park Association

MIT Explores The Science Behind “Outdoor Days”

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Researchers at MIT have devised a new way of looking at the effect global heating has on people’s lives. In the abstract to a study published March 18, 2024 in the Journal of Climate, Yeon-Woo Choi, Muhammad Khalifa, and Elfatih Eltahir write:

Here, we introduce the concept of “outdoor days” to describe how climate change can affect quality of life for different communities and individuals. An outdoor day is characterized by moderate temperature, neither too cold nor too hot, allowing most people to enjoy outdoor activities. The number of “outdoor days” is a non-linear function of the daily surface air temperature. If the latter falls within a specific range describing assumed thermal comfort conditions, then we assign that day as an “outdoor day.”

Using this function, we describe climate change impacts on temperature differently compared to other studies which often describe these impacts in terms of the linear averaging of daily surface air temperature. The introduction of this new concept offers another way for communicating how climate change may impact the quality of life for individuals who usually plan their outdoor activities based on how local weather conditions compare to their preferred levels of thermal comfort.

Based on our analysis of regional variations in “outdoor days”, we present observational and modeling evidence of a north-south disparity in climate change impacts. Under high emission scenarios, CMIP5 and CMIP6 models project fewer “outdoor days” for people living in developing countries, primarily located in low latitude regions. Meanwhile, developed countries in middle and high latitude regions could gain more “outdoor days,” redistributed across seasons.

The reason for the research makes perfect sense, once you think about it. For most people, reading about the difference between a global average temperature rise of 1.5º C versus 2º C doesn’t conjure up a clear image of how their daily lives will actually be affected. The new concept of “outdoor days” makes it easier for non-scientists to appreciate the impact that rising temperatures have on daily life, MIT says.

Outdoor Days Can Lead To A Deeper Understanding

The new “outdoor days” concept describes the number of days per year that outdoor temperatures are neither too hot nor too cold for people to go about normal outdoor activities, whether work or leisure, in reasonable comfort. Describing the impact of rising temperatures in those terms reveals some significant global disparities, the researchers say.

Eltahir says he got the idea for this new system during his hour-long daily walks in the Boston area. “That’s how I interface with the temperature every day,” he says. He found that there have been more winter days recently when he could walk comfortably than in past years. Originally from Sudan, he says that when he returned there for visits, the opposite was the case. In winter, the weather tends to be relatively comfortable, but the number of moderate winter days has been declining. “There are fewer days that are really suitable for outdoor activity,” Eltahir says.

Rather than pre-define what constitutes an acceptable outdoor day, Eltahir and his co-authors created a website where users can set their own definition of the highest and lowest temperatures they consider comfortable for their outside activities, then click on a country within a world map, or a state within the US to get a forecast of how the number of days meeting those criteria will change between now and the end of this century. The website is freely available for anyone to use.

“This is actually a new feature that’s quite innovative,” he says. “We don’t tell people what an outdoor day should be; we let the user define an outdoor day. Hence, we invite them to participate in defining how future climate change will impact their quality of life, and hopefully, this will facilitate deeper understanding of how climate change will impact individuals directly.”

New Discoveries

After deciding that this was a way of looking at the issue of climate change that might be useful, Eltahir says, “we started looking at the data on this, and we made several discoveries that I think are pretty significant.”

First of all, there will be winners and losers, and the losers tend to be concentrated in the global south. “In the North, in a place like Russia or Canada, you gain a significant number of outdoor days. And when you go south to places like Bangladesh or Sudan, it’s bad news. You get significantly fewer outdoor days. It is very striking.”

To derive the data, the software developed by the team uses all of the available climate models, about 50 of them, and provides output showing all of those projections on a single graph to make clear the range of possibilities, as well as the average forecast. When we think of climate change, Eltahir says, we tend to look at maps that show that virtually everywhere, temperatures will rise. “But if you think in terms of outdoor days, you see that the world is not flat. The North is gaining; the South is losing.”

While North-South disparity in exposure and vulnerability has been broadly recognized in the past, he says, this way of quantifying the effects on the hazard (change in weather patterns) helps to bring home how strong the uneven risks from climate change on quality of life will be. “When you look at places like Bangladesh, Colombia, Ivory Coast, Sudan, Indonesia — they are all losing outdoor days.”

The same kind of disparity shows up in Europe, he says. The effects are already being felt and are showing up in travel patterns: “There is a shift to people spending time in northern European states. They go to Sweden and places like that instead of the Mediterranean, which is showing a significant drop,” he says.

Placing this kind of detailed and localized information at people’s fingertips, he says, “I think it brings the issue of communication of climate change to a different level.” With this tool, instead of looking at global averages, “we are saying according to your own definition of what a pleasant day is, [this is] how climate change is going to impact you, your activities.” And, he adds, “hopefully that will help society make decisions about what to do with this global challenge.”

The Takeaway

Being outdoors has several health and wellness benefits, according to the National Recreation and Park Association, which says that as little as 20 minutes a day spent outdoors helps to reduce stress. Nearly all (96%) U.S. adults spend some time outside every day. Age can impact time spent outdoors, with Gen X spending the most time outside and Gen Z spending the least amount of time outdoors. Its research shows that:

  • 58% of U.S. adults spend more than 30 minutes a day outside
  • A third of all U.S. adults spend more than an hour a day outside
  • Gen X (39%) are more likely than adults overall (33%) to spend more than an hour outdoors daily
  • Gen Z (9%) are more likely than adults overall (4%) to not go outside during the day

But of course in order to benefit from being outdoors, temperatures need to be in a range that is comfortable enough for people to enjoy getting outside. The MIT research highlights the disparity between countries in the northern hemisphere and the southern hemisphere. Climate justice is a key consideration in all efforts to counter global warming. This research illustrates how hotter temperatures are putting extra stress on some people but not others.


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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new." You can follow him on Substack and LinkedIn but not on Fakebook or any social media platforms controlled by narcissistic yahoos.

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