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Is Our Allergy Season Changing?

Pollen season is upon us but are changes in our climate changing the allergy season?


Winter sniffles will soon be no more, but that’s small consolation to allergy sufferers around the country. Pollen counts are about to climb upward as plants unfurl their leaves. Climate change has increased pollen counts and the length of the pollen season, trends that are expected to continue through mid-century.

Carbon dioxide plays a big role in pollen production, acting as food for plants. One of the most straightforward ways to analyze its impact on pollen production is to isolate plants in a growing chamber and pump in specific amounts of carbon dioxide. Researchers have done just that, and as this week’s graphic shows, the changes are dramatic.

Although of allergens vary from spring to fall, most of the data in published literature exists around ragweed because of the ability to isolate the effects of carbon dioxide around this species. And with the data, researchers have found that pollen production more than doubled when comparing 1999 carbon dioxide levels (around 370 ppm) to pre-Industrial times when carbon dioxide was much lower (about 280 ppm). In the future, if we continue to emit more carbon dioxide from human activities, pollen counts are likely to rise even higher. The research depicted in the graphic shows a near doubling of pollen counts if carbon dioxide rises to 720 parts per million - a level that projections show could be reached around the year 2075, absent any significant mitigation of emissions.

Pollen season is also lengthening in much of the Midwest according to other research. In the Upper Midwest, ragweed pollen season increased by up to 24 days from 1995-2011. The only locations studied that show a shortening of the season are in the Southern Plains, but the decrease is only by a day, offering little respite for allergy sufferers.

In addition to rising carbon dioxide, higher temperatures are also driving these changes. It might not be the case for parts of the country this year, but the overall trend for warmer early spring temperatures allows plants to get a head start growing and a later first frost allows them to hang on longer. Those trends are expected to continue into the future, and will contribute to a further lengthening of pollen season.

For the more than half of all Americans who have at least one allergy, that's bad news that might bring a tear to their eyes.

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