A study released Thursday predicts more bad air days in the summer for Cleveland , Columbus and eight other eastern U.S. cities if global warming continues unabated.

Those cities are expected to have an increase in unsafe air days caused by ground-level ozone, which is formed from a combination of vehicle and factory pollutants and sunlight and heat.

The analysis was conducted by the Natural Resources Defense Council in partnership with several universities, including Yale and Johns Hopkins, and was published in the scientific journal Climatic Change.

"This is another health affect that global warming is going to have on people," said Dr. Cynthia Bearer, a neonatologist at Rainbow Babies and Children's Hospital in Cleveland . "Smog is a significant pollutant in that it's associated with all sorts of health effects."

But Myron Ebell, director of energy policy for the nonprofit Competitive Enterprise Institute in Washington , D.C. , said the study was "the same old thing" coming from the environmental movement.

"This report is trying to scare the public about global warming through a highly selective use of the facts," Ebell said.

The study predicted that unsafe air days — defined as days when ozone levels exceed an 8-hour quality standard set by the U.S. Environmental Protection Agency — will increase in the two Ohio cities, along with Washington, D.C.; Philadelphia; Greenville, S.C.; Memphis, Tenn.; Virginia Beach, Va.; and Asheville, Raleigh and Wilmington, N.C.

Researchers also concluded that 50 eastern U.S. cities would see a 68 percent, or 5 1/2-day, increase in unsafe air days — which affect asthmatics and cause respiratory problems, particularly in children and the elderly.

"The incidence of asthma is increasing," Bearer said. "There are more kids advised to stay indoors during these bad days."

Bearer believes the study is sound and that it took a conservative approach because it assumes other factors such as emissions to remain constant.

The study involved a computer simulation of the 10 cities. Researchers averaged the air quality from five summers in the 1990s and projected how global warming would effect summertime air quality in 2050, said Kim Knowlton, science fellow on global warming and health at NRDC.

"We think it's important because it isolates this climate only effect," Knowlton said.

Ebell said environmentalists fail to take credit for their own success in improving air quality, adding that the Clean Air Act, while expensive, has worked.

"The amount of days in which American cities are out of compliance with the Clean Air Act for ozone has been declining," said Ebell, whose Competitive Enterprise Institute is funded by corporations from a variety of industries.

Matt Carroll, director of the Cleveland Department of Public Health, acknowledged air quality in northeast Ohio has improved slightly, but said it's still a problem the region has struggled with for decades.

He said the study should serve to show the urgency of the issue.

"It confirms all the concerns we've already had about air quality," Carroll said.