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Scientists have linked a warmer climate to a 70 percent increase in unhealthy summertime ozone levels.

The public soundtrack of the United States of the future could be a discordant symphony of hacking, wheezing, and curses. That's because as the world continues to warm, the number of troublesome high-ozone days throughout the country will likely pile up, say researchers.

Ozone, a principal ingredient in urban smog, forms when sunlight interacts with chemicals emitted by things like factories, power plants, and car engines, as well as vegetation. Using a fancy, new IBM supercomputer, scientists at the National Center for Atmospheric Research in Boulder simulated atmospheric conditions over dozens of coming summers right down to the hour, and what they found was worrisome. The models showed a steady upward trend in ozone levels based on current rates of emissions for its source-chemicals, leading by 2050 to as much as a 70 percent increase in unhealthy ozone pollution during U.S. summers.

There are a few reasons for this projected leap, which is described in a study funded by the National Science Foundation and the U.S. Department of Energy. The atmospheric reactions that create ozone happen at a quicker pace in warmer temperatures (the kind of temperatures, for instance, that've defined the world's recent onslaught of record-hot years). Plants also play a role because sweltering weather prompts them to release more volatile organic compounds, substances that help produce ozone. Methane, another ozone-enabler, has seen a global rise in prevalence; the potent climate-bending gas has more than doubled in atmospheric concentration since the pre-industrial era.

As ozone is most likely to soar to harmful levels in already polluted, heat island-shrouded urban environments, these findings do not bode well for America's major cities. Although the threat affects the country broadly, the scientists see certain regions that already struggle with foul air at risk of long stretches of unhealthy ozone. They say:

Unless emissions of specific pollutants that are associated with the formation of ozone are sharply cut, almost all of the continental United States will experience at least a few days with unhealthy air during the summers, the research shows. Heavily polluted locations in parts of the East, Midwest, and West Coast in which ozone already frequently exceeds recommended levels could face unhealthy air during most of the summer.

"It doesn’t matter where you are in the United States – climate change has the potential to make your air worse," said NCAR scientist Gabriele Pfister, the lead author of the new study. "A warming planet doesn't just mean rising temperatures, it also means risking more summertime pollution and the health impacts that come with it."

Those health impacts range from chest pain to congestion to coughing to shortness of breath. Ozone can worsen serious conditions like emphysema and bronchitis, and is especially harmful for children who have asthma. Breathing in ozone on a regular basis "may permanently scar lung tissue," says the EPA. The damage even stretches over to the world of trees, as certain species exposed to the stuff manifest stunted growth and messed-up leaves, like these guys:

Top image: Los Angeles hides behind a curtain of haze (Rennett Stowe / Flickr). Bottom image courtesy of the National Park Service.

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