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Allergy season growing longer in many Mountain West cities

A map of the U.S. shows the change in growing season days in 203 cities across the country. The majority of cities saw an increase in freeze-free days, which is represented by green circles of varying diameters to demonstrate total increase.
Courtesy Of Climate Central
Since 1970, the growing season lengthened the most in the West by 27 days, measured by the number of consecutive days between the annual last and first occurrences of 32 degrees Fahrenheit temperatures.

A new report shows that allergy season is starting earlier and lasting longer across much of the U.S., including many parts of the Mountain West.

The time between the last freeze of spring and the first freeze of fall is called the “growing season.” That’s when plants grow, flower and release pollen.

Since 1970, the growing season in the West has lengthened by nearly a month on average, according to research group Climate Central. In Reno, Nev., the growing season is now 99 days longer – the largest increase in the nation. Las Cruces, N.M., has experienced the third-biggest increase at 72 days and Boise, Idaho, ranks fifth at 52 days.

Other Mountain West cities have also seen allergy seasons expand significantly over the past 50 years. They include Missoula, Mont. (42 days), Albuquerque, N.M. (39 days), Helena, Mont. (34 days), and Salt Lake City, Utah (24 days). In Cheyenne, Wyo., it’s increased by three days.

Lauren Casey, a meteorologist at Climate Central, said the rise of carbon dioxide in the atmosphere is not only increasing the length of allergy season but also its intensity.

“Plants use carbon dioxide for energy in the photosynthesis process,” she explained. “So if you have more carbon in the atmosphere, you’re going to have healthier plants and healthier plants produce more pollen.”

But that hasn’t happened in all areas of the Mountain West. In Colorado Springs, Colo., the growing season has not increased a single day since 1970. In Denver, it has decreased by 15 days.

Casey said factors like being downwind of mountain ranges can cause some cities to be outliers.

Nationwide, 85% of cities saw an increase, and the growing season lengthened by 15 days on average.

According to the Centers for Disease Control and Prevention, 26% of adults and 19% of children in the U.S. have seasonal allergies.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Kaleb is an award-winning journalist and KUNR’s Mountain West News Bureau reporter. His reporting covers issues related to the environment, wildlife and water in Nevada and the region.
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