Global Warming May Significantly Increase Airborne Allergens

ARLINGTON HEIGHTS, Ill. - A demonstration showing that global warming may significantly increase allergenic ragweed pollen is reported by investigators at Harvard University and Harvard Medical School.

"Ragweed pollen is one of the most abundant airborne allergens in late summer and fall, and it is one of the primary causes of seasonal pollen allergy in North America," said Peter Wayne, Ph.D., Harvard University, Cambridge, Mass.

"We investigated the direct impact of rising CO2 concentrations on pollen production in experimental populations of ragweed to evaluate potential future risks of hay fever and respiratory disease, and to develop strategies to mitigate them," Dr. Wayne said.

Atmospheric CO2 concentration has increased by 29 percent since pre-industrial times, and is expected to double again sometime between the next 50 to 100 years based on current global warming trends according to the report. Plants grown in CO2 enriched atmospheres generally grow faster and larger.

Study investigators collected pollen form ragweed plants (Ambrosia artemisiifolia L.) grown from seed in controlled-environment glasshouses.

"We found pollen production was 61 percent higher in elevated versus ambient CO2 environments. Although these findings suggest that the incidence of hay fever and related respiratory diseases may increase in the future, it's difficult to accurately predict the threat to public health caused by CO2-stimulated pollen production," Dr. Wayne said.

Other environmental factors the investigators expect to change in concert with CO2, such as precipitation and temperature, are likely to influence the growth and distribution of ragweed. Recent models, for example, indicate that global warming trends will favor the spread of ragweed throughout Europe.

"Increased outdoor airborne allergens, as postulated in the ragweed study, adds another dimension to the discussion of the increased prevalence of allergic diseases," said editorial author Richard W. Weber, M.D., National Jewish Medical and Research Center, Denver. "However, it would be premature to assume that increased pollen grain numbers necessarily leads to an increased airborne allergen exposure.

"Studies comparing pollen levels from ragweed plants at different sites have found marked variability. They've also found varying potency in plants at the same site from year to year, which were attributed to seasonal climatic differences, primarily of rainfall," Dr. Weber said.

If the increased pollen grains resulting from the increased ambient CO2 levels are found to maintain the same ratio of allergenic proteins, there may be a more pressing need to modify factors within our control according to Dr. Weber.

Dr. Wayne and his colleagues are currently addressing this issue, analyzing the protein composition of ragweed pollen raised in various environments predicted by current climate change models.

Other investigators in the study are Susannah Foster, B.S., Harvard University; John Connolly, Ph.D., University College of Dublin, Ireland; Fakrhi Bazzaz, Ph.D., Harvard University; and Paul Epstein, M.D., Harvard Medical School, Boston. Current research related to the impact of climate change on allergenic protein composition of ragweed is being led by Christine Rogers, Ph.D., Harvard School of Public Health, Boston.

Source: Annals of Allergy, Asthma & Immunology, the scientific journal of the American College of Allergy, Asthma and Immunology (ACAAI) March 15, 2002