Carbon Dioxide/Ragweed Allergies

By George Grow

This is the VOA Special English SCIENCE REPORT.

An American scientist has shown a link between increased production of ragweed pollen and rising temperatures on earth. Lewis Ziska of the Agricultural Research Service did the study. He found that ragweed plants produce almost two times as much pollen now as they did one-hundred years ago. The study suggests pollen levels could go up another one-hundred percent as temperatures continue to rise over the next century.

Agriculture Secretary Dan Glickman says the study may lead to a better understanding of the effect of high carbon dioxide levels on our environment and human health.

Many scientists say carbon dioxide and other gases are trapping heat in Earth's atmosphere. These gases are released when vehicles, factories and power centers burn fuels like coal, oil and natural gas. An increase in temperatures could raise sea levels. And it could cause serious weather changes such as flooding or periods of dry weather.

An estimated forty-million people in the United States suffer from allergies. Many have allergic reactions to pollen, produced by plants, such as ragweed. Pollen is a reproductive substance produced by flowering plants. It can be carried by the wind. Ragweed pollen is a major cause of allergic attacks in autumn. It causes some people to have trouble breathing. Their eyes may burn and water. They may sneeze a lot.

Mr. Ziska measured pollen levels of ragweed plants grown in the laboratory in different levels of carbon dioxide. He found pollen production rose almost four-hundred percent with a two-hundred percent increase in the amount of carbon dioxide.

Each plant produced an average of five and one-half grams of pollen at carbon dioxide levels that existed one-hundred years ago. At current carbon dioxide levels, each plant produced an average of ten grams of pollen. The study found the pollen count would rise to twenty grams at carbon dioxide levels that scientists expect one-hundred years from now.

Earlier this year, Mr. Ziska moved the experiments out of the laboratory. He is now growing ragweed in three areas in or near the city of Baltimore, Maryland. He says his experiments should show if rising temperatures and carbon dioxide levels already are increasing ragweed pollen.

This VOA Special English SCIENCE REPORT was written by George Grow.

Voice of America Special English