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Scientists devise a new, relatable measure of climate change: "outdoor days”


Scientists devise a new, relatable measure of climate change: “outdoor days”

Their climate forecast: The Global North will gain outdoor days, while the the Global South will lose them.
March 26, 2024

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Climate change will bring more days of pleasant weather to the Global North while subtracting from the tally of nice days in the Global South, according to a new study. The analysis features a new measure of climate change’s impact on daily life in the form of “outdoor days,” denoting days when the weather is mild enough for outdoor work and recreation activities.

Many studies of climate change impacts focus on changes in mean temperature – a measure that has little intuitive meaning for most people – or extreme weather events – which only occur occasionally. The new approach instead emphasizes the quotidian.

“Our findings have important implications for the future of quality of life in different climate regions across the world,” says study team member Yeon-Woo Choi, a postdoctoral researcher at the Massachusetts Institute of Technology.

Choi and his collaborators gathered historical temperature data and projections from nearly 50 different climate models, as well as economic data and global population projections through the year 2100 from existing databases. They calculated the number of days per year that any given point on the globe will experience temperatures between 10 and 25 °C (50-77 °F), now and in the future.

The work is one of only a few studies to consider changes in mild weather at a global scale, and the first to do so using a comprehensive array of climate models.

Today, the populated areas of the world experience an average of about 165 days of mild weather annually (45% of the year), the researchers report in the Journal of Climate. Generally countries in the Global South enjoy more outdoor days than countries in the Global North.

But climate change is altering these patterns. In tropical areas, “outdoor days have decreased by about 13% in the last three decades compared to the period 1961-1990,” the researchers write. “Meanwhile, high-latitude countries have experienced a 13% increase in the number of outdoor days.”

These changes are likely to magnify if high greenhouse gas emissions continue. Countries in the Global South like Brazil, Nigeria, and India will experience a steep loss of outdoor days during the warmest parts of the year.

“Among all countries considered, Bangladesh stands out with a particularly striking reduction of exposure to outdoor days, which may decrease quality of life and cause substantial loss of labor productivity in this country where most of the population primarily depend on agriculture for their livelihood,” the researchers write.

Meanwhile, countries in the Global North will see more mild days in winter albeit fewer in summer. In the European Union this will net out into a small overall increase in outdoor days, while in some countries such as Russia and Canada the overall increase in outdoor days will be quite large.

“This study provides significant evidence of a sharp north-south disparity in observations of outdoor days that is likely to deepen in the future due to climate change under high-emission scenarios,” Choi says.

The idea of outdoor days doesn’t account for the loss of snow in northern climes – which can be a driver of valuable tourism, as well as important culturally.

Still, the findings are consistent with a well-known pattern where countries that have contributed least to climate change in the form of past greenhouse gas emissions suffer most and countries that have contributed most suffer less or even benefit.

One remaining question is how exactly to define ‘mild weather.’ Past studies have done so in somewhat varying ways. But using slightly different temperature ranges in the analysis doesn’t alter the overall pattern of the results, the researchers report.

Since people have different temperature preferences, the researchers also set up a website where users can define outdoor days according to their own preferred temperature range and see how the number of such days will change in their area by the end of the century.

“We are now interested in how climate change will alter the spatial and temporal distribution of outdoor days at local and regional scales,” Choi says. The researchers also plan to investigate the potential effects of shifts in outdoor days on tourism in developing countries in tropical areas.

Source: Choi Y.-W. et al.North-South disparity in impact of climate change on ‘outdoor days’.” Journal of Climate 2024.

Image: Egor Komarov via.

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