Black carbon a powerful climate pollutant: international study

Deborah Zabarenko PlanetArk 16 Jan 13;

Black carbon, the soot produced by burning fossil fuels and biomass, is a more potent atmospheric pollutant than previously thought, according to a four-year international study released on Tuesday.

Emitted by diesel engines, brick kilns and wood-fired cookstoves, black carbon is second only to carbon dioxide as the most powerful climate pollutant, according to the study published in the Journal of Geophysical Research-Atmospheres.

But because black carbon only lasts in the atmosphere a matter of days, compared to carbon dioxide's atmospheric endurance of centuries, addressing it could be prime target for curbing global warming, the report said.

"This new research provides further compelling evidence to act on short-lived climate pollutants, including black carbon," Achim Steiner, chief of the United Nations Environment Program, said in a statement.

Steiner pointed to efforts under way to cut black carbon emissions from heavy-duty diesel vehicles, brick production and municipal waste disposal as part of the international Climate and Clean Air Coalition. The United States was one of the coalition's founders last year.

The U.S. Environmental Protection Agency in mid-December also tightened limits on soot pollution from power plants, diesel engines and burning wood from levels set in 1997.

The report found black carbon's effect on climate is nearly twice what the United Nations Intergovernmental Panel on Climate Change estimated in its landmark 2007 assessment.

At that time, climate scientists ranked black carbon third behind carbon dioxide and methane. The new research, conducted by a multinational team of 31 experts, moves black carbon up in the ranking.

The new assessment found black carbon emissions caused significantly higher warming over the Arctic and other regions, could affect rainfall patterns, including those of the Asian monsoon system, and have led to rapid warming in the northern United States, Canada, northern Europe and northern Asia.

The sooty particles that make up black carbon can be a major component of urban air pollution like that now blanketing Beijing, said Durwood Zaelke, president of the Washington-based non-profit Institute for Governance and Sustainable Development and a reviewer of the study before its publication.

"Black carbon is not only more important for climate than we thought, it also kills over a million people every year who contract deadly respiratory diseases by breathing air polluted by black carbon," Zaelke said in a statement.

The study was published four days after the United States released a draft assessment of the climate, finding that the consequences of climate change are now evident in U.S. health, infrastructure, water supply, agriculture and especially more frequent severe weather.

That report followed a U.S. announcement that found 2012 was the hottest year on record in the contiguous United States, with thousands of individual weather records shattered.

(Editing by Paul Simao)

Climate change: Soot's role underestimated, says study
Matt McGrath BBC News 15 Jan 13;

Black carbon, or soot, is making a much larger contribution to global warming than previously recognised, according to research.

Scientists say that particles from diesel engines and wood burning could be having twice as much warming effect as assessed in past estimates.

They say it ranks second only to carbon dioxide as the most important climate-warming agent.

The research is in the Journal of Geophysical Research-Atmospheres.

Black carbon aerosols have been known to warm the atmosphere for many years by absorbing sunlight. They also speed the melting of ice and snow.
Half a degree

This new study concludes the dark particles are having a warming effect approximately two thirds that of carbon dioxide, and greater than methane.

"The large conclusion is that forcing due to black carbon in the atmosphere is larger," lead author Sarah Doherty told BBC News.

"The value the IPCC gave in their 4th assessment report in 2007 is half of what we are presenting in this report - it's a little bit shocking,"

The researchers say black carbon emissions in Europe and North America have been declining due to restrictions on emissions from diesel engines. But they have been growing steadily in the developing world. However as these type of particles don't last very long in the atmosphere, cutting their number would have an immediate impact on temperatures.

"Reducing emissions from diesel engines and domestic wood and coal fires is a no-brainer as there are tandem health and climate benefits," said Professor Piers Forster from the University of Leeds.

"If we did everything we could to reduce these emissions we could buy ourselves up to half a degree less warming, or a couple of decades of respite," he added.

The report warns that the role of black carbon is complex and can have cooling and warming effects.

"Mitigation is a complex issue because soot is typically emitted with other particles and gases that probably cool the climate," said Prof Forster,

"For instance, organic matter in the atmosphere produced by open vegetation burning likely has a cooling effect. Therefore the net effect of eliminating that source might not give us the desired cooling," he added.

Black carbon is said to be a significant source of rapid warming in the northern United States, Canada, northern Europe and northern Asia. The particles are also said to have an impact on rainfall patterns in the Asian monsoon.

Last year a six nation coalition of countries began a combined effort to curb the impact of short lived climate agents such as black carbon.

The authors say that while cutting back on soot is important, cutting carbon dioxide emissions is the best way to address climate change in the long term.