Cities' Air Quality Takes a Big Hit as Climate Warms

New Study Predicts Summertime Smog, Health Risk Increase Due to Global Warming

WASHINGTON, DC (August 4, 2004) - A comprehensive new analysis by some of the nation's top medical experts projects that residents in more than a dozen U.S. cities will enjoy significantly fewer healthy air days in coming summers as hotter temperatures caused by global warming speed formation of the lung-damaging pollution commonly known as smog. That means more people will have to restrict outdoor activities, while those with asthma and other respiratory troubles face life-threatening results.

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, Heat Advisory: How Global Warming Causes More Bad Air Days, were published today by NRDC (Natural Resources Defense Council), and released in cooperation with Physicians for Social Responsibility's health experts in more than a dozen cities.

"Smog is a persistent air pollution problem for millions of Americans," said Patrick Kinney, associate professor of Environmental Health Sciences at Columbia University's Mailman School of Public Health, and one of the principal authors of the report. "Our research shows that global warming is likely to make this problem even harder to manage."

Smog, also known as ground-level ozone, is formed when pollutants from vehicles, factories and other sources mix with sunlight and heat. The new study confirms that more heat means more smog.

The study analyzed small, medium-sized and large cities in the eastern half of the U.S. The cities analyzed were: Atlanta, GA; Baltimore, MD; Buffalo, NY; Charleston, WV; Charlotte, NC; Chicago, IL; Cincinnati, OH; Detroit, MI; Indianapolis, IN; Little Rock, AR; Louisville, KY; Monroe, LA; Nashville, TN; Pittsburgh, PA; and Portsmouth, NH.

By mid-century, people living in these 15 cities in the eastern United States would see, on average:

  • A 60 percent increase in the number of days when ozone levels exceed the health-based air quality standard set by the EPA (using an 8-hour measurement);
  • A 20 percent drop in the number of summer days with "good" air quality based on U.S. Environmental Protection Agency (EPA) criteria, from an average of 50 days per summer to 40 days per summer;
  • A doubling of "red alert" air quality days from two per summer today to four per summer.

Some of the more notable effects for individual cities are:

  • In Atlanta, by mid-century the number of summer days with "good" air quality would drop by 26 percent -- nine days each year -- from an average of 35 days per summer to 26 days per summer.
  • In Cincinnati, global warming would increase by 90 percent (from 14 to 26) the number of days when ozone levels exceed the health-based air quality standard set by the EPA (using an 8-hour measurement).
  • Louisville would see the highest rise among the study cities for asthma hospital admissions of people under 65 and mortality because of elevated ozone due to global warming.

The deteriorations in air quality examined in the report are due strictly to rising summer temperatures, and do not take into account changing emissions from cars and other sources. The authors will be publishing the underlying research on which the NRDC report is based in peer-reviewed scientific journals this year.

Heightened smog levels trigger asthma attacks and pose health threats to children and the elderly in particular. Increased smog can result in coughing, shortness of breath, pain when breathing, lung and eye irritation, decreased lung capacity, and greater susceptibility to respiratory illnesses in healthy people. For people with asthma, smog pollution can increase sensitivity to allergens. At the same time, the elevated carbon dioxide levels responsible for global warming also stimulate increased pollen production in allergenic plants, such as common ragweed.

"The air in many of our nation's cities is already unhealthy. Hotter weather severely compounds a dangerous problem for millions of Americans," said Professor Jonathan Patz of the University of Wisconsin-Madison and lead author of the report. "People with asthma are especially at risk, but everyone is adversely affected by breathing unhealthy air. The unsettling news here is that global warming could offset some of the positive gains we've been making on air quality."

Changes from year to year in the severity of smog pollution are thought to result largely from variations in weather. For example, the relatively high levels of ozone in the United States during 1988 and 1995 were likely due in part to hot, dry, and stagnant conditions. Conversely, in 2003 we experienced one of our cleanest ozone years, coinciding with an unusually cool, wet summer in the East. In the United Kingdom last year, one quarter to one third of the 2000 deaths during the devastating August heat wave are attributed to pollution (especially ozone) that shot up in concentration with the soaring temperatures.

"We have the technology for cleaner cars and power plants, which will reduce air pollution and fight global warming, " said Dan Lashof, Science Director for NRDC's Climate Center. "This research provides another compelling reason to establish enforceable limits on emissions of heat-trapping gases to ensure that these technologies get to the market."

Scientists say the Earth is warming faster today than at any time in history, and far more rapidly than natural forces can explain. Scientists say the problem is heat-trapping pollution like carbon dioxide. The most recent government data show that 2003 tied 2002 as the second hottest year on record, following 1998. All five hottest years have occurred since 1997. Scientists say average temperatures will warm as much as 10 degrees F by the end of the century unless we start cutting global warming emissions soon. The good news is, we know how to stop the problem. The answer is better technology in our cars, trucks and SUVs, and cleaner, more efficient energy choices like wind and solar power.