Oct. 13, 2008 -- Surface-level ozone, a poisonous gas that claims tens of thousands of lives annually, could get much worse thanks to the effects of climate change, according to new research.
While international treaties like the Kyoto Protocol attempt to curb greenhouse gas emissions and limit the effects of global warming, researchers say ozone is a silent killer that has stayed below the radar.
"It's the third most important greenhouse gas after carbon dioxide and methane," David Fowler of the National Environmental Research Council in the United Kingdom said. "But it's not the biggest one, and it's not the biggest threat to human health -- particulates in the atmosphere are worse. So it's a sort of Cinderella gas that has been mostly ignored."
In Europe alone an estimated 21,400 people die prematurely each year as a result of inhaling too much ozone, which damages lung tissue and exacerbates a variety of respiratory ailments.
In a report published this week by the Royal Society in the UK, Fowler and a team of researchers argue that even though nations like the United States, the U.K., and Japan have taken steps to curtail pollution that causes ozone, global warming will negate their efforts by the year 2050.
In developing countries, the outlook is far worse.
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"If countries like China and India sign up to all of the emissions controls currently planned, things won't get much worse," Fowler said. "But they won't get much better, either. If the controls aren't vigorously applied, ozone could multiply by several factors easily."
Since 1900, background ozone concentrations worldwide have gone from about 10 parts per billion to between 30 and 50 parts per billion today. High in Earth's stratosphere, ozone is crucial to life on the surface, shielding us from harmful solar radiation. When humans and plants breathe it in, though, it's toxic.
Medical doctors argue over whether there is such a thing as a "safe" threshold for ozone, but the World Health Organization says sustained exposure to concentrations over 50 parts per billion is dangerous. The United States Environmental Protection Agency's standard for air quality is 75 parts per billion.
Ozone is not emitted directly from car tailpipes or power plant smokestacks. Instead, it forms when nitrogen oxides interact with other commonly emitted gases like methane, carbon monoxide and volatile organic compounds (VOCs) in the presence of sunlight. As a result, local concentrations vary a lot depending on how much pollution is in the immediate area.
This makes assessing the global effects of climate change on ozone difficult. Some projections for warming predict the planet will heat up by two to three degrees Centigrade by the middle of the century. Humidity is also due to increase as the planet warms, which typically suppresses ozone formation.
But other factors are also at work, Pavan Racherla of Carnegie Mellon University said. For instance, some plants naturally emit a VOC called isoprene. On its own isoprene is harmless, but when combined with nitrogen oxides it readily forms ozone. Warming temperatures will lead to large spurts in plant growth in some parts of the world, and isoprene emissions will add up.
Other parts of the globe are already drying out, and wildfires appear to be intensifying, adding yet another source of ozone to the mix. In 2007, severe wildfires roared through the United States, scorching 13 million acres of land, of which 1.3 million was in California. In a study published this week in Geophysical Research Letters, researchers found that the California fires tripled the number of times ozone in the region exceeded the EPA health standard.
And climate change projections for the 21st century forecast increasingly hot and dry weather for much of North America, exacerbating the threat of fire.
"With climate change and increasing temperature, the effect from wildfires will reach up in magnitude," Gabriele Pfister of the National Center for Atmospheric Research in Colorado, said. "You'll have an earlier snow melt, more drought and a longer fire season."
In Africa and Southeast Asia, for example, biomass burning has already degraded air quality in regions that can hardly afford to get much worse.
"Biomass burning in Africa, and biomass burning coupled with emissions from megacities in Southeast Asia routinely cause ozone episodes of 100 parts per billion and higher," Fowler said. He believes the growing threat is all the more reason to curtail all human-related pollutants as quickly as possible.
"Greenhouse gas reduction will also decrease the amount of oxidants like ozone in the atmosphere," he said. "These problems are all connected, but they are largely ignored by policy makers. We shouldn't pretend the connections don't exist."
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