W A S H I N G T O N, Aug. 16, 2000 -- Allergy sufferers, beware: Global warmingcould bring more hay fever, according to government research thatshows ragweed produces significantly more pollen as carbon dioxideincreases.
The ubiquitous weed makes nearly twice as much pollen now as itdid 100 years ago and will likely double its production again overthe coming century with predicted increases in carbon dioxidelevels, the Agriculture Department study suggests.
“This research may help us better understand the troublingimpact of high carbon dioxide levels on our environment and ourhealth,” Agriculture Secretary Dan Glickman said Tuesday.
About 15 percent to 20 percent of the population has hay fever — or allergic reactions to plant pollen, dust and other airborneparticles — and ragweed is the major cause of the problem in thefall.
Grains Travel Many Miles
The plant is found all over the country and is particularlyprevalent in the Northeast and Midwest. The pollen grains are sosmall that they can travel many miles.
A laboratory study done by USDA in 1998 and 1999 found thatragweed pollen counts went from 5.5 grams per plant atcarbon-dioxide levels that existed in 1900 to 10 grams at currentlevels. At predicted carbon dioxide levels in the year 2100, the pollen countwould reach 20 grams per plant.
Results of USDA’s lab study are to be published in an upcomingissue of World Resource Review, a journal of climate-change issues.
More Study Necessary
Scientists at Harvard University are doing similar research thisyear.
“This is a pretty good first sign” that climate change will bea problem for allergy sufferers, said Cynthia Rosenzweig, a seniorscientist at Columbia University’s Center for Climate SystemsResearch.
Many scientists believe a warming of the Earth has been underway for a century and has accelerated over the past 20 years. Thewarming has been linked to a “greenhouse effect” caused bymanmade pollution and increased concentrations of carbon dioxide inthe atmosphere.
While that could be good for farmers, because higher levels ofcarbon dioxide would increase some crop yields, it also couldaggravate weed problems, and the effects on allergies and otherhealth concerns have not been studied sufficiently, Rosenzweigsaid.
Plants, which use carbon dioxide for photosynthesis, react tothe gas differently. An earlier study found that trees exposed toincreased carbon dioxide grow 25 percent faster than those without it.
The USDA researchers expanded their ragweed study this summer byplanting the weed in controlled conditions outdoors in Maryland.
Plants that were set out in Baltimore, where it is hotter andcarbon-dioxide levels are higher than outside the city, are growingsignificantly faster than at a rural site, said Lewis Ziska, aplant physiologist who is leading the research.
“The ones that are growing in the city are bigger and have morepollen, on the order of a third bigger,” Ziska said.
But even if pollen production does grow as carbon dioxide levels increase,it remains to be seen how that will affect individual allergysufferers, doctors say.
Sensitivity levels vary among people who are allergic toragweed, said Robert Bush, an allergy specialist at the Universityof Wisconsin medical school.
For people who are highly sensitive, “once you reach a certainthreshold, adding more pollen to those people isn’t going to make alot of difference,” he said.