Shedding Light on Black Carbon

Published on
February 20, 2011

Carbon dioxide gets most of the public attention as the main driver of climate change, a serious and increasing threat to public health worldwide.

But "black carbon" or "soot" emitted from diesel engines, cook stoves, brick kilns, agricultural burning and other sources in the developing and developed world poses a serious health risk for people especially in south and east Asia.

Black carbon doesn't last near as long in the atmosphere as carbon dioxide and hence has not been considered a significant greenhouse gas contributor to long-term global climate change. But as described in an assessment being presented by the United Nations Environment Programme (UNEP) this week in Nairobi, black carbon has serious regional climate impacts and massive public health impacts, as it is a form of particulate matter (PM2.5) that causes cardiac and respiratory disease and premature death.

Unlike carbon dioxide that stays in the atmosphere almost indefinitely, black carbon only stays in the atmosphere for a few weeks and hence does not really contribute to the greenhouse gas effect. But it does apparently cause significant warming as it falls to earth and absorbs sunlight, especially in the Arctic where it covers otherwise reflective snow. And there's no doubt about its effect on people's lungs and hearts.

The goal of significantly cutting global carbon dioxide emissions has caused great political turmoil and paralysis on the international and domestic levels. But on the black carbon front, there's good news: reducing black carbon enough to create significant public health and economic benefits is relatively simple, according to UNEP's assessment, which members explained in Washington DC at the American Association for the Advancement of Science on Feb. 20.

The UNEP commission examined 2,000 measures to reduce emissions of black carbon, carbon dioxide, methane, sulfur dioxide and other emissions that affect climate and air quality. They found that 16 relatively simple measures could have significant effects in reducing emissions of black carbon, the powerful but also "short-lived" greenhouse gas methane and the compounds that form ozone, which is also a serious regional health problem.

Black carbon, methane and the precursors to ozone could through these measures be reduced enough to avoid more than 2 million premature deaths, avoid warming of almost a half degree C, avoid more than $5 trillion in economic  mortality damages  and avoid more than 50 million tons of crop losses by 2050, the UNEP commission said.

The measures include installing particle filters on diesel engines and retiring high emissions engines; reducing agricultural burning – instead using crop residue for mulch or other beneficial means; replacing primitive stoves or open fire cooking with cleaner-burning stoves; using briquettes instead of coal for home heating; and retrofitting brick kilns to pipe their emissions underground.

"The recommended measures all use current technologies and are in place in regions around world," said Drew Shindell, a NASA climatologist who chaired the UNEP commission. "This is different than ‘Oh wouldn't it be nice if we could pull carbon dioxide out of the air.' Yes that would be lovely but no one's done it. By contrast we know how to do all these things. Technology is not a barrier."

Methane could also be reduced by aerating rice paddies mid-season to reduce rotting; capturing emissions from landfills, wastewater treatment plants, coal mines and oil refineries; and using bio-digesters to process livestock waste -- measures that also offer localized public health benefits.

Since methods of and results of black carbon reduction are both regional in nature, addressing black carbon also avoids some of the political battles that have characterized the international campaign to reduce carbon dioxide emissions. If India and China reduce their black carbon emissions, they will be the ones also reaping the health and economic benefits...unlike with carbon dioxide, where the effect of climate change is global and developed nations that have already had their industrial revolutions seem to have an unfair advantage.

Along with the immediate health effects from reducing particulate matter, the UNEP commission reported that reducing black carbon emissions significantly would help curb the regional changes in rainfall and other weather patterns caused by deforestation, desertification and other human activities related to climate change. These weather changes, from drought to intense storms, of course have serious and complicated health effects, usually affecting the most impoverished and vulnerable populations.

While the measures identified by the UNEP commission are relatively simple and low cost, in some cases involving behaviors that cost nothing at all, implementing such changes on a wide scale is no easy matter. Getting people to use cleaner–burning brick kilns and cook stoves means reaching people in precarious economic and political situations. And the economic crisis has stalled the implementation of clean diesel programs and other industrial measures.

"Compliance and success varies widely from country to country, depending much on the local circumstances," said Earthjustice attorney Erika Rosenthal.

Kings College London professor Martin Williams noted that "swift action" is especially warranted in the case of black carbon reduction, where reforms taken 30 years in the future will have less beneficial impact than measures taken immediately.

While international bodies and scientists are discussing how to integrate black carbon and other "short-lived climate forcers" or SLCFs into global talks and agreements, local, regional and national governments and NGOs are doing things – from citywide diesel rules to international cook stove programs -- that reduce black carbon, and hopefully will see their efforts bolstered by emerging research.