Get Ready to Itch and Sneeze

As one of 40 million Americans who suffer from hay fever, Lewis Ziska carries an inhaler in his pocket and takes a whiff to clear his lungs on bad allergy days. But hay fever is more than a personal-health issue for Ziska. A weed ecologist with the U.S. Department of Agriculture's Crop Systems and Global Change Laboratory, Ziska is a leading researcher in the fledgling field of allergies and climate change. His findings regarding ragweed, an invasive plant whose pollen is the leading trigger of fall hay fever, are nothing to sneeze at. Global warming and increased atmospheric carbon dioxide from burning fossil fuels appear to supercharge the growth of ragweed. And not only does ragweed grow larger and produce more pollen, its pollen is more allergenic, studies show.

People allergic to ragweed aren't the only ones who'll be sniffling more. Studies show that increased CO2 levels increase the level of tree pollen, a common source of allergies in springtime. There's evidence that warmer temperatures in Alaska have led to increases in yellow-jacket stings, bad news for people with bee-sting allergies. Not even your basement will be safe: fungal spores also proliferate in warmer temperatures and thrive when carbon-dioxide levels rise.

To test his ragweed hypothesis, Ziska planted the weed in three plots: a rural farm, a semi-rural county park and downtown Baltimore. The urban plot's ragweed produced four times the pollen count of the rural site. "Cities already have more carbon dioxide than rural areas and are hotter," Ziska says. "Cities are a surrogate for global warming."

The impact of global warming and increased CO2 on allergies is also being studied by government agencies, scientists and doctors. The Environmental Protection Agency's National Center for Environmental Research is soliciting proposals for climate change and allergy studies to receive funding. The Intergovernmental Panel on Climate Change—the leading international authority on man-induced warming—and the EPA both cited increased allergic reactions due to climate change as a growing concern in 2007 reports.

Allergists are also worried. One new concern: a startling rise in the amount of tree pollen. Warmer temperatures in Europe are causing birch trees to bloom earlier, prompting an earlier and perhaps longer allergy season. Studies at Duke University show that elevated carbon dioxide increases pollen production of loblolly pines. Allergists suspect that record pollen counts are contributing to the onslaught of new allergy and asthma patients. "I'm seeing an epidemic of new cases," says New York City allergist Clifford Bassett.

Christine Rogers of the School of Public Health and Health Sciences at the University of Massachusetts is working with the USDA's Ziska on a study of fungal spores, which cause allergies in about 10 percent of the public. "We have a greater proportion of the public that is sensitive to allergens, so the question of how climate change affects this is ever more important," says Rogers. Fungi—everything from mushrooms in the woods to fungus that grows in damp basements—play an important role in the ecosystem by decomposing plants. If plant biomass increases due to elevated CO2 and global warming, fungi may proliferate as well, they suspect. Fungal spores are problematic because they affect air quality indoors as well as out. Higher temperatures will lead to increased use of air conditioners, which spread spores if improperly maintained. Heavier rainstorms and floods predicted under climate-change scenarios will also increase indoor dampness, allowing fungal spores to proliferate in homes and buildings, according to the 2007 study "Climate Change, Aerobiology, and Public Health in the Northeast United States."