If it seems like everyone’s wheezing these days, that’s because asthma is a growing problem. Though the disease was almost unheard of in 1900, it now affects over 15 million Americans a year and annually kills 180,000 people around the world. In the U.S., the asthma rate has increased 42 percent in the past decade alone. What’s causing this spike? Recent evidence points to the common culprit in so many major environmental woes: greenhouse gases. Global warming is not only threatening to melt the polar ice caps, trigger increasingly violent weather, and throw agriculture into a tailspin, but it’s also emerging as a major factor in the asthma epidemic in a host of surprising ways. “None of the things we used to associate with asthma, like poor indoor air quality and cockroach infestation, have increased that much—but a whole lot of things related to burning coal and oil have. That’s what’s causing this tremendous increase,” says Paul Epstein, MD, codirector of Harvard Medical School’s Center for Health and the Global Environment.
Asthma occurs when the bronchial tubes routinely become so inflamed that the sufferer has difficulty breathing; attacks of wheezing and coughing start in response to allergens in the immediate environment. It tends to set in around preschool-age and improves in adulthood, so children are the most affected. It’s not completely understood why some kids develop asthma and some don’t, but it’s likely a genetic predisposition set off by triggers in a child’s immediate surroundings. Exposure to high levels of some of the allergens that cause attacks—dust mites, pollen, and cockroach infestation— seems to prompt new cases. Recently, the role of immunity has also been emerging as a cause with the “hygiene hypothesis.” This asserts that in our increasingly sterile surroundings, children are exposed to fewer microbes, preventing their immune systems from maturing properly and leaving them vulnerable to both allergies and asthma. But this isn’t enough to account for the dramatic increase in asthma rates, so, in recent years, public health experts have been trying to sort out exactly how the global environment is coming into play.
Scientists first looked into vehicle emissions, since the particulates in exhaust are known to trigger asthma attacks. They found that auto emissions don’t just make kids who already have asthma more miserable a 2002 study from researchers at the University of California at San Francisco and the Natural Resources Defense Council (NRDC), showed that diesel particles are able to alter human immune systems in ways that can actually cause new asthma cases to develop, a finding that is corroborated by epidemiological evidence of higher asthma rates along truck routes and near bus depots. (This is one factor —along with more cockroaches, mold, and mildew—that explains why poorer children, especially those in inner cities, are disproportionately affected. Their asthma rates are up to twice as high as average; in one part of Harlem in New York City, one in four children were recently found to have the disease.)
For many scientists, the real surprise is how asthma rates are being driven up by a more pervasive consequence of our fossil-fuel consumption: global warming. “It appears that smog created by warmer temperatures not only triggers attacks in those who have asthma, but also causes children to develop asthma in the first place,” says Gina M. Solomon, MD, a senior scientist with the NRDC. This was first made alarmingly clear in a 2002 study from the University of Southern California School of Medicine that looked at the effects of ozone smog, which is caused by emissions from cars and industry; in a vicious circle, it’s also exacerbated by higher temperatures. In that study, researchers followed children with no history of asthma in 12 California communities for five years and found that the kids who played outdoor sports in the communities with the highest ozone levels were three times more likely to develop asthma than the kids who didn’t play sports outside. The effect was not seen in the areas with lower ozone. “The combination of being active outdoors and being in a highozone area is toxic to kids’ health,” says Solomon.
More troubling evidence came from a major study in Occupational and Environmental Medicine. Researchers evaluated more than 650,000 children throughout Western Europe and demonstrated that those exposed to higher levels of indoor humidity — something that increases along with outdoor temperature—are more likey to develop asthma. A ten-percent humidity increase was found to cause a 3 percent increase in asthma rates (most likely because of the resulting increase in mold and dust mites). And earlier this year, Epstein and his colleagues explored how pollen levels would be affected by the higher carbon dioxide expected to come along with higher temperatures. When ragweed was exposed to the CO2 levels we’re expected to hit in the next 30 to 60 years, pollen production increased 60 percent. Epstein says that other high-pollen weeds will likely respond in similar ways. Add this all to the simple fact that warmer temperatures will cause increasingly earlier springs — which means a prolonged allergy season with more high pollen count days and more attacks — and you’ve got a recipe for an ever-worsening epidemic.
Of course, none of this is good news — but there is hope that the more that scientists learn about how air pollution and global warming are affecting our health, the better chance that more people will be motivated to care for our environment. After all, it wasn’t until the health effects of lead became known that we saw laws banning its use in gasoline and paint. “This issue will be considerably more complicated, of course,” says Epstein, “but calling attention to health issues can drive us to healthy solutions.”
• The Natural Resources Defense Council’s Clean Air & Energy Campaign (nrdc.org/air/pollution) features in-depth reports on air quality, frequent news updates on pollution and clean energy issues, and an “activism toolbox.”
Clear the air
Keep your home clean and fresh
Identify food sensitivities
Eat a nutrient-rich diet
Don’t overuse antibiotics
Story by Sarah Bridges. This article originally appeared in Plenty in March 2008. The story was added to MNN.com.