Climate change creates longer ragweed season

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Climate change creates longer ragweed season

By Deborah Zabarenko – Mon Feb 21, 5:44 pm ET

WASHINGTON (Reuters) – A changing climate means allergy-causing ragweed pollen

has a longer season that extends further north than it did just 16 years ago,

U.S. scientists reported on Monday.

In research that gibes with projections by the U.N. Intergovernmental Panel on

Climate Change, plant and allergy experts found that ragweed pollen season

lasted as much as 27 days longer in 2009 than it did in 1995. The further north

in the Western Hemisphere, the more dramatic the change in the length of pollen

season.

Ragweed pollen can cause asthma flare-ups and hay fever, and costs about $21

billion a year in the United States, according to the study published in the

Proceedings of the National Academy of Sciences.

" This is not something that's hypothesized, this is not something that's

modeled, this is not something that may or may not occur depending on the math

that you do, " said study author Ziska of the U.S. Department of

Agriculture. " This is something that we're actually seeing on the ground in

recent years. "

Even in places where ragweed season didn't lengthen or even shortened slightly

-- such as Texas, Oklahoma and Arkansas -- there was lots more pollen, which

caused more intense symptoms, said co-author Dr. Jay Portnoy of the Allergy,

Asthma and Immunology Section at Children's Mercy Hospital, the University of

Missouri-Kansas City School of Medicine.

Ragweed is probably not the only pollen likely to have a longer season as the

planet warms, Portnoy said in a telephone interview.

LATER FROST, MORE POLLEN

" We used ragweed as a marker but it's probably true for other pollens too, " he

said, including tree pollen that causes allergy symptoms in the U.S. spring.

Ragweed pollen was a reasonable marker because its season is naturally easy to

track.

It's what's known as a short-day plant, which begins blooming when the days

start getting shorter, that is, after the Northern Hemisphere summer solstice

around June 21. It stops flowering with the first frost.

As global average temperatures have warmed, the first frost has been delayed,

especially at higher latitudes, which has meant a longer season for ragweed.

Because warming is greater at these high latitudes, the length of the season has

been more pronounced.

For example, in town, Texas, the ragweed season actually shrank by 4 days

between 1995 and 2009. But further north in Papillion, Nebraska, it got 11 days

longer; in Minneapolis, it was 16 days longer, and in Saskatoon, Saskatchewan in

Canada, the season was 27 days longer.

Ziska said he was surprised by how big the change was in such a relatively short

period of time: " I thought maybe 10 days, or a couple of weeks, but to see it up

to almost 4 weeks was kind of interesting. "

This could mean a change in the way ragweed-triggered allergies are diagnosed

and treated. Clinicians who are unaccustomed to checking their patients for

ragweed-related symptoms will likely have to start doing this.

" Things that used to be a fairly minor disease are now going to be a much more

significant problem, " Portnoy said.

SOURCE: http://bit.ly/S1eCH Proceedings of the National Academy of Sciences,

online February, 2011.

http://news./s/nm/20110221/hl_nm/us_climate_ragweed