High carbon dioxide levels may be increasing pollen

Abnormal plant growth linked to rise in asthma


WASHINGTON - High concentrations of carbon dioxide in city air may be stimulating abnormal growth of ragweed and other plants that aggravate childhood asthma, health experts warned yesterday.

Although the incidence of asthma has increased among all age groups, the sharpest increase has been among children under 4 years old, according to the Centers for Disease Control and Prevention.

CDC reported in 1998 that between 1980 and 1994, incidence of the respiratory disease among pre-schoolers increased by 160 percent.

Harvard Medical School researcher Christine Rogers said the increase, which appears to be most severe among city children, may be related to the fact that carbon dioxide causes some highly allergenic plants to produce abnormal levels of pollen.

"There is no evidence that ragweed pollen causes asthma," Rogers said, "but allergens from pollen and fungus spores have certainly been associated with exacerbation of existing disease."

In addition, she said, measurements over some cities have recorded concentrations of carbon dioxide drastically higher than the worldwide average, she said.

Such a "carbon dioxide island" effect could cause ragweed to produce much more pollen than it would if grown in lower concentrations of carbon dioxide, she said.

This latest warning about the effects of climate change prompted Rogers, fellow Harvard researcher Paul Epstein and American Public Health Association Executive Director Georges Benjamin to call for policies and research specifically directed toward urban climate change.

Produced by the combustion of fossil fuels such as coal, oil and natural gas, carbon dioxide has increased steadily in the atmosphere.

The concentration was measured at 379 parts per million at the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii a month ago.

That was an increase of 3 parts per million since last year and roughly 100 parts per million since the pre-industrial age, scientists say.

Rogers said carbon dioxide levels over Baltimore, Phoenix and New York have been measured at as high as 600 parts per million during atmospheric inversions.

It was not clear to what extent temporary increases would cause plants such as ragweed to produce more pollen.

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