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Cleaning the Air Helps Cool the Planet

Emissions cuts offer "greatest potential for substantial, simultaneous improvements in local air quality and near-term mitigation."
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©iStockphoto.com/Warwick Lister-Kaye

Local and state regulators have new ammunition in the fight to justify expensive air pollution rules: Cutting smog and soot has an immediate impact on climate change.

A study published last week bolsters the link between air quality and climate, finding that across-the-board cuts in air pollution can spur "substantial, simultaneous improvement" in local air quality and near-term mitigation of climate change.

Trimming smog and soot also represents an alternate and far more immediate global warming solution for regulators stymied by the complexities of other greenhouse gases such as carbon dioxide, said Drew Shindell, a climate scientist at NASA's Goddard Institute for Space Sciences and the lead author of the study.

Tackling air pollution can buy 20 to 30 years worth of mitigation, he said—time that will be needed, if ongoing debates in Poznan, Brussels and Washington D.C. offer any indication—to cut the political and economic knots associated with carbon dioxide.

The health benefits also make a strong case for action to countries that have so far resisted climate mitigation for its own sake. These pollutants—soot, ozone, and smog-causing volatile organic compounds and nitrogen oxides—have well-documented effects on human health. Trimming emissions produces easily quantifiable benefits.

"This is no substitute for targeting carbon dioxide, which in the long run is the main contributor" to climate change, Shindell said. "But if you want to have any effect in the near-term, ... the short-lived pollutants can have very large impacts."

The climate-warming effects of these short-lived pollutants have largely been ignored by scientists and regulators focusing on climate policy. Carbon dioxide, with a lifetime of many centuries, is the star of that show, and the effects on climate by these other pollutants, which endure for mere months, are less well understood.

Regulators also have no way to quantify—as they must when making public health rules—the cost and benefit of climate mitigation. It's impossible to put a cost, for instance, on averting global temperature rise by a few thousandths or even hundredths of a degree.

Still, a collective focus on limiting these pollutants could substantially affect 21st century climate. Several climate models, Shindell and his colleagues showed in a study published last Monday in the journal Atmospheric Chemistry and Physics, suggest that reducing air pollutants in both North America and Asia can produce an immediate cooling effect on climate—certainly far faster than any action on longer-lived emissions like carbon dioxide. "It's much, much faster, as fast as it could possibly be," Shindell said.

Regulators are noticing. President-elect Barack Obama's transition team on Thursday got briefed on emissions and climate and is exploring what tools federal agencies need to better mitigate impacts, said Ellen Baum, a senior scientist with Clean Air Task Force, a Boston-based non-profit that has spent years trying to link climate and urban pollution.

On Thursday California approved the most aggressive plan in the nation to slash greenhouse gas emissions and meet state climate targets. Regulators continue that work today, voting to force 1 million big rig owners to clean up diesel exhaust. Both state rules carry climate and health benefits.

"We are now incorporating the climate change benefit, if there is one, into our environmental analysis and staff reports when we propose new regulations," said Sam Atwood, spokesman for the state's South Coast Air Quality Management District, charged with improving air quality for 17 million people in the four-county Los Angeles basin.

That can be "difficult and dicey," he cautioned. "There are not a lot of protocols for different kinds of climate-change gas reductions.... Every time we propose a tough regulation, we have to make a very strong case for why the benefits outweigh the costs."

Tools and calculations for measuring public-health benefits are robust and well established; climate mitigation, in contrast, is in its infancy. But in a system structured to maximizing health goals, throwing climate in the mix could change priorities - even without quantification, many experts note.

Ground-level ozone, or smog, is one example, said Baum of the Clean Air Task Force. It's a powerful greenhouse gas. But the nation's health-based rules generally focus on reducing peaks, while every-day background most affects climate.

"It's a wave versus sea-level thing," Baum said. Health officers are focused on reducing the wave—the late-afternoon summertime ozone spike—but Baum and others would like to see more effort aimed at reducing the sea-level, or background. "Reducing background ozone isn't the best strategy for reducing ozone peaks, but if we reduce background, there will be a reduction in the peaks as well," she said. "It's a tough nut to crack, though. It's not going to be easy."

Black carbon, or soot, is another example. A byproduct of diesel engines, soot is a tough pollutant to reduce. Regulators can often obtain the same health benefit by focusing on other easier-to-control compounds, like sulfates from power plants.

But sulfates cool the atmosphere. Black carbon has a well-established warming effect. Add that information, and imposing limits on black carbon start to look a little more palatable, regulators and scientists say.

The benefits extend far beyond the United States' borders. Growing emissions from Asia represent an enormous percentage of near-term climate change, Shindell and others note. Their emissions, particularly soot, have far-flung impact—from shrinking Arctic icepack to prolonged droughts in America's breadbasket.

Evidence quantifying that impact on the Arctic will be disclosed this week at the American Geophysical Union's fall meeting in San Francisco. Researchers with the National Oceanic and Atmospheric Administration have found that the "Arctic haze"—a soup of aerosols, ozone, volatile organic compounds and other industrial pollutants—contributes to the shrinking icepack and changes ice flow dynamics during the spring melt.

But what's exciting, Shindell notes, is the potential for rapid change. Carbon dioxide takes decades to mix, adjust and start to warm the planet. These short-lived pollutants start to affect the Earth's climate almost instantly; turning them off produces rapid mitigation.

The good news, say researchers, is that the divisions between climate research and air quality and long-term versus short-term impacts are disappearing. "You will see over the next few years that this is going to get a lot more focus," said Gabriele Pfister, a scientist studying wildfires at the National Center for Atmospheric Research in Boulder, Colo. "We know now you can't look at short-term effect without looking at long-term effect."

Douglas Fischer is editor of DailyClimate.org. E-mail him at dfischer@dailyclimate.org

This article originally ran at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.

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