Study links longer allergy season to climate change

Allergy sufferers are suffering a bit longer each year in the Red River Valley due to climate change, according to a new study. The U.S.

Allergy sufferers are suffering a bit longer each year in the Red River Valley due to climate change, according to a new study.

The U.S. Department of Agriculture study tracked weather and pollen data from 1995 to 2009 at 10 sites across central North America, including Fargo, Minneapolis and Winnipeg.

Researchers crunched the numbers and came to a surprising revelation: the ragweed pollen season has been extended by 16 days in Fargo and Minneapolis and by as much as four weeks in Winnipeg and Saskatoon, Sask.

All tracking sites at latitudes above the 44th parallel north, a line that cuts through South Dakota and southern Minnesota in the Midwest, showed significant increases. But the reverse was true the farther south researchers went. Spots in Texas and Arkansas saw their allergy seasons decrease by three or four days.

It's an important trend to watch, analysts say, because surveys show at least 10 percent of U.S. residents are ragweed sensitive and the plant is believed to cause more hay fever than all other plants combined.


Dan Dalan, allergist and owner of Allergy and Asthma Care in Fargo, has tracked ragweed pollen counts since 1995 and provided data for the study. He said the new findings are "amazing" because they show the allergy season is getting longer, a fact that's hard to notice from year to year.

The study tracked seasonal changes in temperature, including the number of frost-free days each spring and summer and delays in the first frost of the fall, and found a link between weather shifts and the extended ragweed season.

The first frost marks the beginning of the end of the ragweed pollen season in North Dakota, but Dalan said allergy sufferers have to wait until "everything's covered up" by snow before they get complete relief from the troublesome powder.

Mark Ewens, data manager with the National Weather Service, tracked more than 100 years of weather data for Grand Forks and Fargo to determine the amount of consecutive spring and summer days above 38 degrees, the temperature that frost can form.

His analysis shows the frost-free season is now much longer on average than it was in the late 1800s, the start of the cities' weather records.

From 1900 to 1920, Grand Forks' average frost-free season was 74.6 days. That average jumped to 95.9 days from 1950 to 1970 and was extended again to 105.4 days from 1990 to 2010.

The same is true in Fargo, which saw its average frost-free season increase from 136.9 days in the 1970s to 146.3 days from 1990 to 2010.

Dalan said there isn't much allergy sufferers in the region can do about the longer season.


"We can't control Mother Nature, but we can at least know Mother Nature. You just might have to use your medications for a couple of weeks longer."

Ryan Johnson writes for the Grand Forks Herald

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