Allergy season may lengthen due to recent latitudinal warming in Central North America, which has increased the length of the ragweed (Ambrosia spp.) pollen season, according to a study published in Proceedings of the National Academy of Sciences on Monday, Feb. 21.
Ragweed pollen is a major allergen. Of the Americans allergic to pollen-producing plants, 75 percent are sensitive to ragweed, according to the Asthma and Allergy Foundation of America (AAFA).
Mike Tringale, vice president of AAFA, said this equates to 35 million hay fever sufferers out of the 50 million Americans with allergies, according to Scientific American.
In the new study, the team of North American researchers found that higher latitudes are warming faster than middle latitudes in North America, causing a proportionate increase in the duration of the ragweed pollen season.
Season length mainly increased with the delay in first frost of the fall season and a longer frost free period due to latitudinal effects.
"Overall, these data indicate a significant increase in the length of the ragweed pollen season by as much as 13–27 d at latitudes above 44°N since 1995," the study abstract reads. "If similar warming trends accompany long-term climate change, greater exposure times to seasonal allergens may occur with subsequent effects on public health."
"It's not just theoretical," said lead researcher Lewis Ziska, a plant physiologist at the U.S. Department of Agriculture's crop system and global change laboratory, according to Scientific American. "We are seeing a signal based on what in fact the [U.N. Intergovernmental Panel on Climate Change] is predicting."
Tringale said a longer season is dangerous because it can tax hay fever sufferers' immune systems. Allergies can sometimes also trigger asthma attacks.
"With the longer season, with the creeping breadth of the geographic footprint of the season, and with more powerful plants producing more pollen, it's a triple threat," Tringale said, according to Scientific American. "Now you've got yourself a much wider population that could potentially be affected that might not have been affected before."