TUESDAY, March 26, 2002 (HealthDayNews) -- Get ready for worsening allergies as the century progresses.
Increasing carbon dioxide levels associated with global warming may lead to a rise in the incidence of ragweed and other plant allergies within the next 50 to 100 years, according to a study in the March issue of Annals of Allergy, Asthma and Immunology.
Concentrations of carbon dioxide, which causes global warming, have already increased 29 percent since pre-industrial times and are expected to double between 2050 and 2100.
This is apparently good for plant reproduction, but not for human respiratory health.
"This seems to be something across the board -- that plants love carbon dioxide, but then they allocate more to their reproductive organs, and the side effects are something we're just beginning to think of," says Dr. Paul Epstein, one of the study authors and the associate director of the Center for Health and the Global Environment at Harvard Medical School.
"One of the things that some of the climate-change skeptics have said is that carbon dioxide is wonderful for us. Plants love it," Epstein adds. "That is correct, but [the skeptics] do not understand that it changes the way that they grow and that that can be harmful."
Few studies have looked at the relationship of climate change, plants, and public health. But this study corroborates the findings of another recent study, which found that excess carbon dioxide tripled the number of pine cones and seeds produced in a pine forest in North Carolina.
Additional research by Lewis Ziska of the U.S. Department of Agriculture also finds that ragweed responds both to warmer temperatures and to increased carbon dioxide. This research is being conducted in the field, and not in a laboratory environment.
In this experiment, the researchers grew ragweed, one of the primary causes of seasonal pollen allergies in North America, in a greenhouse that was supplied with twice the normal level of carbon dioxide. The plants produced 61 percent more pollen than ragweed grown in a greenhouse with normal levels of the gas.
The carbon dioxide also apparently did not influence the average size of pollen grains.
"The things we inhale are fine particles. If you get more pollen but each grain is heavier, it'll just fall out of the atmosphere and deposit on the ground, but you won't inhale it," explains Dr. Jonathan Patz, director of the Program on Health Effects of Global Environmental Change at Johns Hopkins Bloomberg School of Public Health in Baltimore.
That means more inhalable grains, which, Patz says, "would be bad for public health."
The trend could have implications not just for allergy sufferers but also for asthmatics.
Airborne allergens can exacerbate asthma as well as hay fever. "Asthma statistics have doubled from the 1980s to the 1990s," Epstein says. "We've mostly been concerned about indoor air pollution. This raises whole other issues."
This is not the first health impact to be associated with the changing global environment. Outbreaks of malaria, dengue fever and equine encephalitis are thought to be connected to climactic shifts. The thinning ozone layer is expected to result in an increase in the number of melanomas worldwide.
No one can be sure exactly how the earth's plant life will react to future climactic changes and how that will translate into a public health impact, but this early evidence does seem to indicate that respiratory diseases will be on the rise.
"This is very much about our environmental and energy policies," Epstein says. "The real point is that the burning of fossil fuels -- coal and oil, principally -- is having some unexpected side effects on our health. This is a whole new aspect to global change that is playing a role."
What To Do
The National Institute of Allergies and Infectious Diseases has reader-friendly information on pollen and allergies and asthma.
Or check out the Spring Allergies and Asthma Survival Guide from the American Academy of Allergy, Asthma and Immunology.
Johns Hopkins University has lots of current research on global environmental health.
