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Study: Climate change linked to longer pollen season

By Wendy Koch, USA TODAY
Updated

Is your hayfever getting worse each year? Researchers report a link Monday between global warming and a lengthening in North America's ragweed pollen season that may be affecting millions of allergy sufferers.

The ragweed season is now up 27 days longer than in 1995 in the northernmost areas, because the first frost comes later in the fall and thus extends the frost-free period, according to a study by 20 researchers -- mostly U.S.-based -- published in the latest journal of the Proceedings of the National Academy of Sciences.

"We knew already that springtime was coming 10 to 14 days earlier than it did 20 years ago. But this new work measures the length of the ragweed pollen season in the US for the first time, and finds it's getting longer as temperatures rise," writes study co-author Kim Knowlton, a scientist at the Natural Resources Defense Council and a professor at Columbia University's Mailman School of Public Health.

"The effect is greater the farther north one goes," she says. "If these warming trends continue (as they're projected to) under a changing climate, the health of people with severe allergies or asthma could really suffer."

At least 10% of the U.S. population is sensitive in the summer and fall to ragweed, which along with tree and grass pollen can cause hayfever and asthma, and many of those people can expect more uncomfortable days, the report says.

The researchers analyzed U.S. and Canadian data on ragweed and daily temperatures at 10 different latitudes. They found that in eight of the areas, and in all seven of those north of 40 degrees latitude, the number of days in the ragweed pollen season increased between 1995 and 2009. In all but one case (Oklahoma City), the further north, the longer the season.

For example, the area studied that was furthest south -- Georgetown, Texas -- the season was actually four days shorter and in Rogers, Ark., it was three days shorter. Yet in Oklahoma City, Okla, it was one day longer. Further north, in Papillion, Neb., it was 11 days longer; in Madison, Wis., it was 12 days; in LaCrosse, Wisc, 13 days; in Minneapolis, Mn., and Fargo, N.D., 16 days. In Canada's Winnipeg, it was 25 days longer, and in Saskatoon, 27 days.

"There was a highly significant correlation between latitude and increase in the length (days) of the ragweed pollen season over the period from 1995 to 2009," concluded the report, whose lead authors include Lewis Ziska of the U.S. Department of Agriculture and Christine Rogers of the University of Massachusetts, Amherst.

Knowlton advises allergy sufferers like herself to check local pollen conditions before heading outside, and after spending time outdoors, to change clothing and wash hair as well as bedding to minimize contact with pollen.

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