Specialists 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.

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.

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.