Study shows black carbon is major warming culprit

Sept. 20, 2011, 3:51 a.m.

Black carbon is the second leading cause of global warming after carbon dioxide, according to research by professor of civil and environmental engineering Mark Jacobson.

Jacobson presented his research on black carbon’s effects on global warming at the Aug. 31 meeting of the American Chemical Society (ACS), the world’s largest scientific society.

Black carbon, commonly called soot, is particulate matter pollution released from combustion reactions in diesel engines, as well as burning biofuels and biomass.

Though it lasts in the atmosphere for a short amount of time, approximately a week, compared to carbon dioxide’s lifespan of 30 to 40 years, it is about a million times more effective at trapping heat in the atmosphere, Jacobson said.

“I estimate that black carbon is causing 15 to 20 percent of global warming,” he said, estimating that carbon dioxide is responsible for 40 percent, and methane for 15 percent.

The study, funded primarily by the U.S. Environmental Protection Agency (EPA) and partially by the National Aeronautics and Space Administration (NASA), has been used to analyze ways to reduce Arctic ice melt. Recent reports have shown that Arctic ice is at its lowest level since levels were first measured in 1972.

Due to its short, weeklong lifespan, curbing emissions of black carbon would have an immediate impact on the global climate and is the most effective way of quickly reducing Arctic ice melt, Jacobson said.

Like many attempts to slow global climate change, however, there remain significant hurdles in getting international cooperation on reducing black carbon emissions.

The United States has taken steps to curb these types of emissions, such as the Diesel Emission Reduction Act, signed into law by President Obama at the beginning of this year.

The EPA’s own analysis of money spent on the Diesel Emissions Reduction Act concluded that for every $1 spent on curbing diesel emissions, $13 were saved through averting negative environmental and health effects.

However, Jacobson noted that only about six percent of black-carbon emissions come from the U.S. Much of the world’s emissions come from developing countries, where wood-burning stoves and heating systems emit black carbon emissions and regulatory standards on heavy equipment is much less stringent.

Donald Kennedy, professor of environmental science, emeritus, and a senior member of the Academic Council, agreed that the major hurdle is getting the international community on board with new regulations.

“There is a clear regulatory responsibility domestically for the problem of diesel emissions,” Kennedy said. He noted, however, that efforts to stem the problem are getting international support.

“I don’t think there’s a lot of international opposition to it, but getting everybody to take the same position on it would require a serious, treaty-making operation,” Kennedy said.

In addition to the environmental effects of black-carbon emissions, there are also serious negative health consequences.

“Biofuel health effects are about eight times higher than [the effects of] simple fossil fuels,” Jacobson said. This is due to the fact that much biofuel burning occurs in heavily populated cities, where people are more concentrated and more likely to breathe in air of poor quality.

It is estimated that 25 to 35 percent of global black-carbon emissions come from China and India.

Brendan O’Byrne

Brendan is a senior staff writer at The Stanford Daily. Previously he was the executive editor, the deputy editor, a news desk editor and a writer for the news section. He's a history major originally from New Orleans.

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