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Allergies Health Center

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Global Warming May Worsen Allergies

Researchers Say Rising Carbon Dioxide Levels Will Up Pollen Production
WebMD Health News
Reviewed by Louise Chang, MD

June 6, 2006 -- We all may be sneezing, sniffling, and scratching more in decades to come, due to global warming.

Harvard researchers say that higher levels of the greenhouse gas will also boost pollen production, causing allergy sufferers to suffer even more in the future.

Just last week, Duke University researchers reported that rising atmospheric levels of carbon dioxide will likely fuel the growth of a more poisonous form of poison ivypoison ivy.

The researchers studied the growth of ragweed under conditions mimicking both today's levels of atmospheric carbon dioxide and those projected for the future, assuming that climate change continues at its current pace.

Early Arrival of Spring

They found that the ragweed plants grown under the futuristic conditions produced about 55% more pollen than the plants grown under conditions more closely approximating today's climate.

Researcher Christine A. Rogers, PhD, tells WebMD that global warming is already having an impact on the growing season, with the arrival of spring occurring earlier in most places. This, combined with an increase in carbon dioxide levels, will result in longer, more intense allergy seasons in the future, she says.

"The clearest signal of global climate change is the earlier onset of spring," she says. "Our goal was to examine the interaction between the lengthening of the growing season and the increase in carbon dioxide."

More CO2, More Pollen

In their effort to do this, Rogers and colleagues grew ragweed seeds in climate-controlled greenhouses and carefully measured pollen production.

The air we now breathe has about 350 parts of carbon dioxide per million parts of air. Experts expect carbon dioxide levels to double within the next three to six decades, so the researchers studied ragweed growth at both 350 parts and 700 parts carbon dioxide per million parts of air.

They also released the ragweed seeds at different times to simulate early and late growing seasons.

A longer growing season was associated with an increase in pollen production for seeds grown at atmospheric carbon dioxide levels that were similar to current conditions. But it seemed to have less impact when seeds were exposed to the highest carbon dioxide levels.

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