BOSTON—Rates of hay fever and other allergic diseases could increase dramatically by century’s end if nothing is done about global warming, the authors of a new study warn. Their experiments show that production of allergenic pollen by ragweed climbs 61% when atmospheric carbon dioxide levels are doubled, a global warming–related event predicted to occur between 2050 and 2100.[1]

In plants, increased ambient carbon dioxide concentrations result in such changes as increases in net photosynthetic rate and water use efficiency. These metabolic changes add up to both faster growth and larger size.

A major rise in allergic disease would be no surprise under these conditions, said Fakhri Bazzaz, PhD, one of the study authors and the Mallinckrodt Professor of Biology at Harvard University in Boston. “Unless we curb the amount of CO2 we emit into the atmosphere, the situation may eventually become dire,” he told RESPIRATORY REVIEWS.

ASSESSING CARBON DIOXIDE’S EFFECT

The authors grew ragweed to maturity in environmentally controlled greenhouses, randomly assigning each plant to ambient or double-ambient carbon dioxide environments (350 or 700 parts per million). Both groups of plants were grown at the same temperatures and received the same amounts of light and water.

Besides producing far more pollen, the plants in the carbon dioxide–enriched environment tended to be larger than those grown in the ambient environment. Although the size differences between the two groups of plants did not always reach significance (multiple measurements of size were obtained), the difference in pollen production was highly significant.

ALTERNATE FUELS NEEDED

The study results resemble the findings of Ziska and Caulfield, who reported an even greater increase in pollen production by ragweed grown in a double-ambient carbon dioxide environment.[2] The combined data will be used to more accurately predict the potential for allergic disease in the future and to develop strategies to mitigate the threat.

Predicting allergic disease as it relates to carbon dioxide exposure will never be easy, though. That, said Professor Bazzaz, is because atmospheric carbon dioxide is influenced by many factors that are difficult to forecast (eg, temperature, precipitation, and pollution). These factors would probably also influence the location and quantity of plant species and thus which populations would be exposed to various allergen types.

A lot also depends on the energy policies of the federal government, which could help to slow the buildup of carbon dioxide in the atmosphere by encouraging the development of alternatives to coal, oil, and natural gas since combustion of those fuels produces large amounts of carbon dioxide. “If we do not do that, the situation will not be very good,” Professor Bazzaz stated.

—Timothy Begany