"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."