If allergy season feels like it’s starting earlier and lasting longer in North Carolina, scientists say the data backs that up.
A warming climate is extending the time plants can grow and release pollen, stretching allergy seasons across much of the United States. In the Triangle, the growing season is now more than a month longer than it was in the 1970s.
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Researchers track the “freeze-free growing season,” the period between the last freeze in the spring and the first freeze in the fall. As temperatures warm, that window is expanding.
Climate Central analyzed temperature data from 198 U.S. cities and found the freeze-free growing season has lengthened in 87% of them since 1970. On average, cities have gained about three additional weeks.
In the Raleigh-Durham area, the season has grown by about 41 days.
That can be good for crops and gardens," WRAL meteorologist Elizabeth Gardner said. "But it also means that our pollen season is longer.”
For allergy sufferers, that can mean longer stretches of symptoms.
Raleigh regularly ranks among the most challenging places in the country for seasonal allergies, according to the Asthma and Allergy Foundation of America.
The region’s dense tree canopy contributes to high pollen levels each spring.
“When we get to the springtime, they all release pollen," Gardner said.
Many people associate allergy symptoms with the bright yellow layer of pine pollen that coats cars and sidewalks each spring.
“A lot of people think that yellow pine pollen is the allergen,” Gardner said. “But it’s actually many other trees releasing pollen at the same time.”
Weather patterns can also influence how intense a particular allergy season becomes. Sudden warm spells in late winter or early spring can cause pollen levels to rise quickly.
“Already last week we started to see the tree pollen go to high,” Gardner said. “With several days in the 80s, it’s likely to skyrocket over the next few days.”
Scientists say climate change is not only lengthening pollen seasons but may also make them more intense.
Rising carbon dioxide levels in the atmosphere can increase pollen production in some plants, particularly grasses and ragweed.
“Warming temperatures are helping make allergy seasons start earlier, last longer and really just feel worse,” Climate Central meteorologist Shel Winkley said.
Seasonal allergies affect about one in four adults and one in five children in the United States, according to the Centers for Disease Control and Prevention. Pollen is also a major trigger for asthma, which affects millions of Americans.
Tree pollen typically peaks in North Carolina in early spring, followed by grasses later in the spring and summer and weeds such as ragweed in the fall.
As temperatures continue to warm, scientists say allergy seasons are likely to keep expanding — meaning more days each year when pollen levels are high.