Climate change is bad news for people with allergies: a warmer climate means a longer pollen season. In just 15 years, the pollen season of one common allergen has lengthened by as much as 27 days in some parts of North America.

The prevalence of allergies is increasing in the United States, but linking this increase with climate change has been a stretch. A team led by Lewis Ziska at the US Department of Agriculture in Beltsville, Maryland, compared readings of ragweed pollen (pictured) since 1995 at 10 stations across North America with changes in temperature and first frost. They found a clear link between recent warming and the length of the pollen season. What's more, the farther north they looked, the greater the extension to the season — so allergy-prone Canadians should consider buying tissues in bulk.


Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1014107108 (2011)