Climate change will result in more days of mild weather in the Northwest United States and fewer in the South and Southeast, according to a new study. Nationwide, pleasant days are projected to occur less frequently in the summer and more frequently during the spring and fall.
The findings employ a relatively new measure of climate impact known as the “outdoor day,” meaning a day when the weather is moderate enough for people to be outside without sweating or shivering, a good day to work outdoors or enjoy activities like walking, jogging, and bicycling.
The concept captures the impact of climate change on people’s everyday lives better than other commonly investigated measures of climate change, such as changes in mean temperature or extreme weather events, the researchers argue.
Earlier this year, the team published a global-scale analysis of outdoor days, reporting that climate change is likely to reduce the number of pleasant days for much of the Global South, and slightly increase pleasant days in some northern countries.
In the new study, the researchers divided the continental United States into nine regions and used multiple global climate models to project how many outdoor days will occur in different parts of the country in a worst-case scenario of continued high greenhouse gas emissions or a best-case scenario of a dramatic and rapid emissions cuts.
The team defined an outdoor day as one with a temperature ranging from 10-25 °C (50-77 °F). But what constitutes pleasant weather is somewhat subjective, so they also built a website where users can analyze trends in outdoor days defined according to their own personal preferences.
In recent decades, people living in the continental United States have enjoyed an average of 172 outdoor days per year, the researchers report in the journal Geophysical Research Letters. Not surprisingly, a preponderance of outdoor days happen in summer (about 56 days on average), and more southerly states like California and Florida have more outdoor days compared to states in northern regions of the country.
With continued high emissions, climate change will alter the seasonal distribution of outdoor days in the United States. There will be many fewer outdoor days during the summer, late spring, and early fall when conditions become too hot for comfort, and somewhat more during early spring, late fall, and especially winter, the analysis reveals.
Although climate models suggest relatively similar trends in average warming across the United States, the effects of climate change on daily life as seen in outdoor days will be different from region to region. “We project relatively large drops in southeast (− 23%), south (− 19%), and Ohio Valley (− 19%), and a significant increase in northwest (14%) toward the end of the century,” the researchers write.
The researchers also looked at correlations between temperature and National Park visitor statistics, and found that visits are higher on pleasant days. This suggests that changes in the number and distribution of outdoor days could have a real economic impact in tourism-dependent areas, as well as affecting residents’ quality of life, they argue.
However, in the best-case scenario of rapid emissions cuts, which would result in net-zero carbon emissions in the second half of the century, the changes in outdoor days would be relatively minimal, reducing the disruptions to daily life and economic risks.
Source: Choi Y.-W. et al. “Climate Change Impact on ‘Outdoor Days’ over the United States.” Geophysical Research Letters 2024.
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