A series of studies by the U.S. Department of Agriculture (USDA) and academic institutions offers accumulating evidence that climate change is both lengthening and intensifying pollen seasons in many parts of the United States.
Carbon dioxide (CO2) in the atmosphere directly affects plants by supplying the carbon they need for photosynthesis. In some cases, elevated CO2 Âlevels can help plants grow fasterâ€”a potential boon when that plant is an agriculturally important species.
But as USDA and other scientists pointed out in a 2009 Environmental Health Perspectives (EHP) study, CO2 â€œdoes not discriminateâ€ between desirable and undesirable plants. That means that while there may be benefits to faster-growing species like forest trees, for example, there can be serious negative consequences when these growth spurts occur Â in other plants, like ragweedâ€”a plant to which at least ten percent of the U.S. population is sensitive.
Some studies suggest that carbon-induced growth increases may be especially great in some pest plant species. The U.S. Global Change Research Program cited in its most recent National Climate Assessment, for example, that when exposed to the same heightened CO2 levels, poison ivy growth increases are nearly five times those in tree species.
Itâ€™s also been shown that higher atmospheric CO2 Âlevels as well as warmer temperaturesâ€” two key aspects of climate changeâ€”may be contributing to the intensification of pollen seasons. A recent field study, for example, found that both factors â€œsignificantly influenceâ€ pollen production in common ragweed and can increase pollen concentrations in the atmosphere.
Other science tells us that some plant species are not only producing more pollen, but are also doing so over longer periods of timeâ€”an effect thatâ€™s already being seen on the ground. In a recent study published in the Proceedings of the National Academy of Sciences, USDA researchers and others found that in parts of North America, the ragweed pollen season is up to three weeks longer than it was in the mid-1990â€™s because of climate change.
â€œThis finding is just one demonstration that plants respond to climate change in ways that are likely to affect people,â€ said Dr. Lewis Ziska, a scientist at USDAâ€™s Agricultural Research Service (ARS) and author of the PNAS study. Â
â€œWe study these aspects of plant responseâ€”from weeds, to wheat, to cellulosic biofuelsâ€”so that growers can continue to effectively provide our supply of food, feed, fiber and fuel, and so that citizens and health professionals can predict and deal with health impacts in the face of climatic uncertainty.â€
While the magnitude of climate-change impact on allergic disease is not yet known, the Centers for Disease Control and Prevention, and other research institutions suggest that there could be a â€œsubstantial effect.â€
â€œThese documented increases in pollen exposures are one of the clearest examples of how a changing climate is already affecting the health of people in the United States," said Dr. John Balbus, Senior Advisor for Public Health at the National Institute of Environmental Health Sciences, adding that other climate-induced ecosystem changes could result in additional health challenges.
"Just as trees and weeds respond to a changing climate, so too do ticks, mosquitoes, and other carriers of human diseases, making it critical that we anticipate all these changing patterns of disease and protect those most vulnerable."
Today, allergic disorders, including asthma, comprise the 6th leading cause of chronic illness in the Nation. They affect more than 50 million Americans per year and cost the United States nearly $20 billion annually. Given the number of studies documenting and projecting longer and more intense pollen seasons as a result of increasing temperatures and CO2 levels, we can expect those impacts and costs to grow even larger if the Nation and the world do not address climate change aggressively.