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Climate Change Extends Allergy and Asthma Season


If you suffer from ragweed pollen allergy or asthma, you have probably noticed over the last several years that your symptoms seem to last longer. It’s not your imagination – the ragweed pollen season lasts longer today than it did just 16 years ago due to climate change and global warming.

Pollen Season Has Extended by Almost a Month in Some Areas

Lewis Ziska, a plant physiologist with the US Department of Agriculture, and his team of researchers identified 10 locations along a north-south transect from Austin, Texas to Saskatoon Canada that had at least 15 years of data. They compared pollen data, the number of frost-free days, and the delays in the onset of the first fall frost.

They found that the ragweed pollen season lasted as much as 27 days longer in 2009 than it did in 1995. And the further north you are in the Western Hemisphere, the more dramatic the length of the season.

Read: Managing Your Seasonal Allergy Symptoms

Ragweed is most commonly found in the warmer regions of the Northern Hemisphere and in South America. It begins blooming when the days begin getting shorter and warmer and stops flowering with the first frost. As global average temperatures have warmed, the first frost is delayed, especially at higher altitudes, lengthening the amount of time pollen is in the air.

Higher carbon dioxide levels associated with global warming may have also doubled the amount of pollen that ragweed produces, causing more intense symptoms. Pollen production has risen almost 400% over the past four or five decades, according to Ziska’s estimates.

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Ragweed pollen can cause asthma flare-ups and hay fever, but even if you aren’t allergic to ragweed, study co-author Dr. Jay Portnoy says that ragweed is probably not the only pollen to have a longer season.

“We used ragweed as a marker,” Dr. Portnoy said, “but it’s probably true for other pollens too. He notes that tree pollen is another type of allergen that causes spring allergy symptoms.

Read: Asthma Impact on Children Differs by Country

Dr. Portnoy says that this could have a significant impact on the way ragweed-triggered allergies are diagnosed and treated. Currently, one in ten Americans test positive for ragweed sensitivity and allergies cost Americans $21 billion annually, according to estimates by the Centers for Disease Control and Prevention.

But according to Patrick Kinney of Columbia University, pollen exacerbates disease and can cause sensitization in people that aren’t yet allergic.

“Things that used to be a fairly minor disease are now going to be a much more significant problem,” added Dr. Portnoy.

SOURCE: Proceedings of the National Academy of Sciences, online February, 2011.