Dark clouds ahead
Global warming is likely to cause hotter summer days and more smog for many cities in the eastern half of the U.S., medical experts said in a study released last week.
The finding raises concerns that the nation's battle against smog could become increasingly difficult; more than 100 million Americans already live in counties with unhealthy smog levels.
Smog is formed when pollutants from vehicles, factories and other sources mix with sunlight and heat.
There is growing scientific evidence linking smog to asthma and other respiratory ailments, with children and the elderly at greatest risk of breathing problems from exposure to smog. More than 17 million Americans have asthma, including an estimated five million children.
"Hotter weather severely compounds a dangerous problem for millions of Americans," says Prof. Jonathan Patz of the University of Wisconsin-Madison and lead author of the report. "The unsettling news here is that global warming could offset some of the positive gains we have been making on air quality."
The analysis was prepared by researchers at the Johns Hopkins University and Columbia University, in collaboration with researchers at Yale University, University at Albany-State University of New York, and University of Wisconsin-Madison. Results of the study were published by the Natural Resources Defense Council and released in cooperation with Physicians for Social Responsibility.
By the end of this century, U.S. government scientists estimate that much of the eastern United States will see increases in the heat index -- the combination of heat and humidity into effective temperature -- in the range of five to 15 degrees Fahrenheit.
The study analyzed the effects of global warming on air quality in the following 15 cities in the eastern half of the United States: Atlanta; Baltimore; Buffalo, N.Y.; Charleston, W. Va.; Charlotte, N.C.; Chicago; Cincinnati; Detroit; Indianapolis; Little Rock, Ark.; Louisville, Ky.; Monroe, La.; Nashville, Tenn.; Pittsburgh; and Portsmouth, N.H.
Researchers compared the 1990s concentration of ozone, the key ingredient in smog, with climate simulations for five-year spans in the 2020s, 2050s and 2080s. The study found all cities in the study had more or the same number of unhealthy smog days.
By mid-century people living in these cities would see, on average, a 60 percent increase in the number of days -- from 12 to nearly 20 -- when ozone levels exceed the U.S. Environmental Protection Agency's (EPA) air quality standard.
In addition, these cities are likely to see a 20 percent drop in the number of summer days that meet the EPA's good air quality standard, from the current average of 50 days per summer to 40 days per summer, as well as a doubling of red alert air quality days from two per summer today to four per summer. On red alert days, individuals are advised to limit outdoor activity.
The study noted that Nashville, for example, would see up to 14 more red alert summer days and Portsmouth would see two "purple alert" days per summer -- the most severe, and rare, health advisory that advises individuals avoid outdoor activity.
The researchers found that global warming could deliver a dangerous double blow to people with asthma.
Smog pollution can increase sensitivity to allergens, and the elevated carbon dioxide levels responsible for global warming also stimulate increased pollen production in allergenic plants, such as common ragweed.
The deterioration in air quality examined in the report is due solely to rising summer temperatures predicted by climate change models and do not take into account reductions in smog forming pollution.