MIT researchers identify "Outdoor Days" when temperatures just right for outdoor activities

MIT researchers develop new way to describe the number of days per year that outdoor temperatures are just right for normal outdoor activities.

Outdoor days: not too hot nor too cold
The new study, which allows users to define too hot or too cold temperatures, defines how many days are just right for normal outdoor activities. Photo by Jessica Rockowitz on Unsplash

Researchers at MIT have developed a new way to quantify the impact of rising temperatures caused by climate change. Dubbed “Outdoor Days”, it 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 in reasonable comfort.

The measure provides a tangible way to describe what global climate change patterns, in specific regions around the world, will mean for people’s daily activities and their quality of life. It also reveals some significant global disparities, the researchers say in the Journal of Climate.

User defined

The idea for Outdoor Days was prompted by Elfatih Eltahir, professor of civil and environmental engineering at MIT, and his hourlong daily walks in the Boston area: “That’s how I interface with the temperature every day.”

Recently, Eltahir noted there had been more winter days when he could walk comfortably than in previous years, but the opposite was true when he visited his native Sudan. The weather in winter is usually relatively comfortable, but the number of these clement winter days has decreased. “There are fewer days that are really suitable for outdoor activity,” Eltahir says.

Outdoor days: not too hot nor too cold
These two maps show the projected change in annual outdoor days in the United States in 2071-2100 with respect to 1976-2005. The two maps are based on two versions of the Coupled Model Intercomparison Projects (CMIP). The hatch-marked areas indicated that more than 80% of models agree on the sign of the change. Credit: Courtesy of the researchers

For this study, researchers developed a website which allowed users to select their country within a world map (or state within the US) and obtain a forecast of how many acceptable Outdoor Days the area would see between now and the end of this century. However, unique to this research is that users could define the highest and lowest temperature they considered comfortable for their outside activities.

“This is actually a new feature that’s quite innovative,” Eltahir 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.”

North-South divide

Once they established this as a useful way of looking at climate change, the researchers studied the data and “made several discoveries that I think are pretty significant,” Eltahir says. Firstly, there will be winners and losers, with the latter likely 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.”

Although this North-South inequality in exposure and vulnerability is well known, this way of quantifying the effects on the change in weather patterns helps to illustrate how strong the uneven risks from climate change on quality of life will be, Elthair says. The same kind of disparity is also illustrated in travel patterns in Europe: “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 adds.

Eltahir says by giving people this level of detailed and localised information “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. Hopefully that will help society make decisions about what to do with this global challenge.”