Climate Fact: Are Rising Temperatures Extending Allergy Seasons?

If you’re one of the 10-20 percent of Americans who suffer from seasonal ragweed allergies, the latest climate change research won’t be welcome news – especially if you live in the Upper Midwest.Scientists have discovered that today’s ragweed pollen season, which peaks in the summer and fall, is as much as 27 days longer than it was in 1995 in northern parts of the North American heartland. Additionally, the duration of these seasonal extensions has increased from south to north which is consistent with the disproportionate warming trends that scientists have observed at higher latitudes. For example, Papillion, Nebraska’s ragweed pollen season has grown by 11 days, Fargo’s has increased by 16 days and Winnipeg’s has increased by 25 days.

These allergy seasons are getting longer because frosts are occurring less often and beginning later than they did several decades ago. Longer pollen seasons increase the amount of time that people are exposed to allergens, meaning that more people may develop ragweed allergies and symptoms may last for longer periods of time. Additionally, longer ragweed growing seasons could eventually produce more pollen, which could also increase the severity of seasonal allergies.

Photo: Common Ragweed. Jim Pisarowicz, National Park Service.

(Source: Ziska, Lewis et al., 2011. “Recent warming by latitude associated with increased length of ragweed pollen season in central North America.” Proceedings of the National Academy of Sciences, 108:10, 4248-4251.)

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