Properly done, moving to reduce black-carbon soot has immediate climate and public-health benefits, she says. But the uncertainties surrounding some of its climate effects remain large.
Rather than serving as an excuse for inaction, however, the uncertainties should to serve as a guide for research, she adds.
For example, the processes that produce soot also produce not only CO2 emissions but also other particles that can cool the atmosphere, she notes. In other words, emissions from any one source may contain competing influences on global warming.
The fingerprints "of human actions on climate are more complex than just the CO2 story," she says.
Concern over the climate effects of black-carbon soot date back to at least 1971, when interest began to grow in the role small particles, or aerosols, could play in Earth's climate system.
During the past decade or so, however, field studies of soot's effect as a climate warmer typically yielded estimates two to three times higher than the effect seen in climate models, notes Veerabhadran Ramanathan, a professor of atmospheric and climate science at the Scripps Institution of Oceanography in La Jolla, Calif.
With this new study, "we're coming closer to what we think black carbon is doing to the planet's climate," says Dr. Ramanathan, who was not a member of the team that pulled together the new analysis but has been studying the impact of soot on the climate for much of his career.
The soot comes from a mix of sources that varies by region. The study notes that roughly 90 percent of global soot emissions fall into several broad categories: diesel-fueled vehicles; use of coal to heat or cook in homes; small kilns and industrial boilers; burning wood or other biomass for cooking; and open burning of biomass, such as using fires to clear forests for farming.