Global Warming's High Carbon Dioxide Levels May Exacerbate
Ragweed Allergies By Don
August 15, 2000
WASHINGTON, Aug. 15--The U.S. Department of Agriculture released
research results today indicating higher carbon dioxide (CO2) levels associated
with global warming may have doubled the amount of pollen that ragweed
produces--mostly over the past four or five decades. Another doubling could
occur by the end of this century.
"This research may help us better understand the troubling impact
of high carbon dioxide levels on our environment and our health," said
Agriculture Secretary Dan Glickman.
In scientific studies, pollen production rose almost 400% with a
200% increase in the amount of CO2. Findings show that high CO2 levels have
increased the potential production of ragweed pollen and may produce pollen
earlier. The ragweed pollen season is now underway.
Lewis H. Ziska, a plant physiologist with USDA's
Agricultural Research Service, did the
pollen counts on ragweed grown in indoor chambers at various levels of
atmospheric CO2, from about the turn-of-the-century levels of 280 parts per
million (ppm) to today's levels of 370 ppm to future predicted levels of 600
ppm. Pollen production went from 5.5 grams to 10 grams to 20 grams as CO2 moved
through these three levels.
This past spring, Ziska moved the experiments outside, growing
ragweed at three locations in the Baltimore, Md., area chosen for their range
in temperatures: Baltimore, typical of urban areas thought to be both heat
islands and zones of high CO2 concentrations; a suburb; and a rural area.
Ziska, conducting his research in collaboration with
Johns Hopkins University School of Public
Health, Towson University and
Multidata Corporation, says this
ongoing experiment should show how global warming and higher CO2 levels might
already be increasing ragweed pollen counts, especially in cities. Although
less ragweed grows in cities, exposure to air pollutants such as ground-level
ozone can make people more sensitive to ragweed pollen.
Scientific contact: Lewis H. Ziska, ARS
Laboratory, Beltsville, Md., phone (301) 504-6639, fax (301) 504-6626,