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Last updated on April 18, 2014 at 1:21 EDT

Allergy Season Longer Due To Climate Change

February 22, 2011

Warmer temperatures and later autumn frosts have been the main sources for why the ragweed allergy season in North America has grown two to four weeks longer than usual, according to researchers.

Northern regions of the United States and Canada have seen a dramatic rise in the length of the allergy season between 1995 and 2009, said researchers, who published a report in Tuesday’s issue of the Proceedings of the National Academy of Sciences.

Saskatoon, in Saskatchewan, Canada had the longest pollen season on record, adding 27 days in 2009 compared to 1995. Winnipeg, Manitoba had a 25-day increase in the same period. And in Fargo, North Dakota and Minneapolis, Minnesota, both saw allergy seasons that extended 16 days.

But further south, in Rogers, Arkansas and Georgetown, Texas, allergy seasons decreased by several days.

The increased period for pollen seasons in the northern latitudes were consistent with the UN’s Intergovernmental Panel on Climate Change projections of increased warming in areas closer to the Arctic, according to the study.

“Latitudinal effects on increasing season length were associated primarily with a delay in first frost of the fall season and lengthening of the frost-free period,” said the study. “Overall, these data indicate a significant increase in the length of the ragweed pollen season by as much as 13-27 days at latitudes above 44 degrees north since 1995.”

For the study, scientists used pollen measurements from the US National Allergy Bureau and Canada’s Aerobiology Research Laboratories. They also took data from US weather stations, Environment Canada and the Canadian National Climate Data and Information Archive.

As many as 30 percent of Americans suffer from ragweed allergies, mostly during warmer seasons. The cause of the allergies comes from a family of plants in the genus Ambrosia, whose flowers send off tiny particles of pollen that the body treats as a threat.

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