Black Carbon

Although not a greenhouse gas, Black Carbon (soot) has emerged as a leading contributor to rising temperatures worldwide, scientists say. Limiting these emissions is seen as a relatively cheap and quick way to reign in warming in the short term. The role of black carbon has only recently been recognised – it was not mentioned as a factor in the UN’s major 2007 report on climate change but in October 2009, the UN environment program called for cuts in black carbon output. Evidence from studies in the Arctic Circle and the Himalayas add a new dimension to global warming’s accelerating pace. The UN reports that 50% of the emissions causing global warming are from non-CO2 pollutants. (Farming is also responsible for serious fine particle pollution.(Pictured A brick kiln spews soot in Kabul, Afghanistan.)



  • Background information
  • Climate and Clean Air Coalition
  • Reports on black carbon’s impact
  • Science ongoing
  • Around the world
Background information

April 2018: Important treaty – which adds black carbon – could be ratified this year. The Gothenburg Protocol established in 1999, sets limits on nasty pollutants like sulfur dioxide, nitrogen oxides, ammonia and volatile organic compounds, which are hazardous to human health. (Some also contribute to global warming). The pact was amended in 2012 to include black carbon, as the world became more aware of the threat it posed. It still needs six countries before it becomes official policy, which may happen this year. The United States was an early adopter, just two days before President Trump took office. link

Recent scientific studies have found black carbon – a component of soot that comes from the burning of fossil fuels and plant materials – to be a key cause of climate change. Black carbon has a strong warming effect both in the atmosphere, and when it lands on snow, ice caps and glaciers, where it absorbs the sun’s heat, reduces reflectivity and causes widespread and faster melting, causing sea level rise and other climate changes.

Black Carbon comes from diesel engines, industrial smokestacks and residential cooking and heating stoves. Most black carbon that falls in the Arctic comes from North America, Europe and Asia. Because black carbon air pollution is also a leading cause of respiratory illness and death, controlling emissions will save lives and improve health around the world. In India alone, black carbon-laden indoor smoke is responsible for over 400,000 premature deaths annually, mostly of women and children. The U.S. and Europe must lead on this issue by committing to stricter standards at home for diesel engines and other sources of black carbon pollution, and by committing to increased financial and technological assistance to the developing world to reduce black carbon pollution from diesel, home cooking and heating and other sources. Norway’s foreign minister said action on black carbon was even more urgent than that on CO2: “Even if we turn the rising curve of greenhouse gas emissions in the coming years, the reduction will not occur quickly enough to preserve the polar and alpine environments. We must address short lived climate pollutants such as black carbon.”  link 

Because black carbon remains in the atmosphere for only a few days – unlike other greenhouse gases, which may remain in the atmosphere for over a century – reducing black carbon emissions may be among the most effective near-term strategies for slowing global warming and avoiding some of the most imminent climate change tipping points. Decreasing black carbon emissions should be a relatively cheap way to significantly curb global warming. Replacing primitive cooking stoves with modern versions that emit far less soot could quickly end the problem. Controlling traffic in the Himalayan region should help ease the harm done by emissions from diesel engines. Yet the United Nations Framework Convention on Climate Change does not address the contribution of this important global warming pollutant. link

March 2018: Black carbon’s role in Arctic warming. Black carbon stays in the atmosphere for just days to weeks, but it can do a lot of lasting damage. The contribution to warming by one gram of black carbon is 100 to 2,000 times more than one gram of CO2 on a 100-year timescale. A 2011 study by scientists from NASA’s Goddard Institute for Space Studies found that as much as a quarter of Arctic warming is caused by black carbon. Another 2015 study found that, like methane, black carbon is responsible for about a half a degree Celsius of warming in the Arctic. link

Climate and Clean Air Coalition

Climate and Clean Air Coalition. (CCAC)
The CCAC was launched by Secretary of State Hillary Clinton in February 2012 to address pollutants that are short-lived in the atmosphere such as black carbon, methane and HFCs which responsible for a substantial fraction of current global warming with particularly large impacts in urban areas and sensitive regions of the world like the Arctic, and have harmful health and environmental impacts. F
ounding members were Bangladesh, Canada, Ghana, Mexico, Sweden, the US and UNEP.

April 2012: The first CCAC meeting which convened in Stockholm, Sweden, welcomed Colombia, Japan, Nigeria, Norway, the European Commission and the World Bank as new partners. The coalition aims to take fast action to reduce short lived climate pollutants that have a direct impact on climate change. According to UNEP, the Coalition agreed on five transformation initiatives aimed at accelerating action on health, crop and climate-damaging pollutants. Approved initiatives include: fast action on diesel emissions including from heavy duty vehicles and engines; the upgrading of old inefficient brick kilns that cause black carbon emissions; accelerating the reduction of methane emissions from landfills; speeding up cuts in methane and other emissions from the oil and gas industry; and accelerating alternatives to hydrofluorocarbons (HFCs), through fast-tracking environmentally-friendly and cost effective alternatives and technologies. link

May 2016: Farms a major source of air pollution. A new study says that emissions from farms outweigh all other human sources of fine-particulate air pollution in much of the United States, Europe, Russia and China. The culprit: fumes from nitrogen-rich fertilizers and animal waste that combine in the air with industrial emissions to form solid particles. link

July 2012: Seven more countries join anti-soot campaign. At a meeting in Paris, the CCAC announced seven new members – Britain, Denmark, Finland, France, Germany, Italy and Jordan. link    

Studies of black carbon impact

August 2013: Cutting soot and methane may not provide much help for climate. A new study said that extra measures to short-lived air pollutants such as soot and methane, would cut temperature rises by only 0.16 degree Celsius by 2050, far less than some estimates that the benefits could be 0.5C. “Reductions of methane and black carbon (soot) would likely have only a modest impact on near-term global climate warming,” the authors at the U.S. Department of Energy’s Pacific Northwest National Laboratory.  link  

May 2013: Efforts to inventory black carbon. Researchers are about to take a big step toward better understanding a tiny air pollutant. A U.N. expert panel earlier this month agreed on a technical road map that will guide the first multinational effort to create a standardized emissions inventory of black carbon, a kind of microscopic soot particle. Scientists say that black carbon emissions play an important but poorly understood role in both global climate change and air pollution. Fifty-one nations, including the United States and members of the European Union, abide by the Geneva Convention on Long-range Transboundary Air Pollution. link

April 2013: Climate scientists may have to rethink some of their old assumptions about carbon. Charcoal and other forms of black carbon do not, as previously thought, stay where the are buried. U.S. and European researchers have just established that black carbon, soot and biochar, the burnt remains from countless forest fires, doesn’t stay in the soil indefinitely. Around 27 million tons of the stuff gets dissolved in water and washed down the rivers into the oceans each year. Black carbon or biochar has been hailed as one possible way of limiting greenhouse gas emissions, by taking carbon out of circulation. Forest, bush, scrub and peat fires produce somewhere between 40 and 250 million tons of black carbon every year. link   

How serious is black carbon?  

January 2013: Black carbon potentially twice as bad as originally thought. “Black carbon” (soot) is said to be the second most important man-made agent of climate change and may have twice the impact on global warming than previously thought, according to a new study. Huge quantities of man-made soot enter the atmosphere every year. Around 7.5m tonnes was released in 2000 alone, according to estimates. It has a greenhouse effect two-thirds that of CO2, and greater than methane. The biggest source of soot emissions is the burning of forest and savannah grasslands. But diesel engines account for about 70% of emissions from Europe, North America and Latin America. link

June 2011: Black carbon emissions 3 to 5 times greater than previously thought. New evidence shows that black carbon soot may be even more damaging to the Himalayan region of the world. Black carbon soot is a potent climate pollutant that is causing up to half the warming in the Arctic region, and also much of the warming in the Himalayan-Tibetan Plateau, two super critical ecosystems that are warming two to three times faster than the global average. The Tibetan Plateau, the planet’s largest store of ice after the Arctic and Antarctic, is warming about three times the global average, with temperature increases of 0.3ºC or more per decade measured for the past half-century. link

February 2012: US leads new initiative to reduce global soot. Led by the United States, a small group of countries is starting a program to reduce emissions of common pollutants that contribute to rapid climate change and widespread health problems The plan will address short-lived pollutants like soot (also referred to as black carbon), methane and hydrofluorocarbons that have an outsize influence on global warming, accounting for 30 to 40% of global warming. Scientists say that concerted action on these substances can reduce global temperatures by 0.5 degrees Celsius by 2050 and prevent millions of cases of lung and heart disease by 2030. The United States intends to contribute $12 million and Canada $3 million over two years to get the program off the ground and to help recruit other countries to participate. link

June 2012: New EPA standards to come into effect. (The new standards came into effect December 14 2012) In 2006, EPA said the revised 24-hour exposure standard would yield $9 billion to $76 billion a year in health and visibility benefits in 2020. Health benefits include reductions in premature death, diseases and symptoms associated with fine particulate pollution exposure, such as asthma attacks and strokes, the agency said. link

September 2011: Reducing soot second most important factor in global warming. A new study of dust-like particles of soot in the air, now emerging as the second most important, but previously overlooked, factor in global warming, provides fresh evidence that reducing soot emissions from diesel engines and other sources could slow melting of sea ice in the Arctic faster and more economically than any other quick fix. Calculations indicate that controlling soot could reduce warming above parts of the Arctic Circle by almost 3 degrees Fahrenheit within 15 years which would virtually erase all of the warming that has occurred in the Arctic during the last 100 years. link

February 2011: UN recommends targeting ‘black carbon’ to tackle climate change. A new report from the United Nations environment programme has concluded cutting the amount of soot we pour into the atmosphere, and emissions of methane from agriculture, would be one of the most powerful ways to tackle climate change. Preventing “black carbon”, particles of soot from industry and cooking fires, from polluting the air would help to cut global warming by as much as 0.5C, and reduce warming in the Arctic by about two thirds by 2030. link

Science ongoing

December 2012: The EPA tightens the nation’s soot standards by 20%, a move that will force communities across the country to improve air quality by the end of the decade while making it harder for some industries to expand operations without strict pollution controls. The new rule limits soot, or fine particulate matter, which stems from activities ranging from burning wood to vehicle emissions, and which causes disease by entering the lungs and bloodstream. Fine particulate matter measuring less than 2.5 micrometers in diameter, or one-thirtieth the width of a human hair, ranks as the country’s most widespread deadly pollutant. The new rule is a result of a 2009 court ruling that said the EPA standards for the amount of soot permissible in the air on an annual average ignored the advice of scientific advisers by maintaining the standard established in 1997 and must be re-written. That limit was 15 micrograms per cubic meter of air. The EPA cut the level to 12 micrograms per cubic meter. link

September 2010: NASA – does heating from black carbon increase cooling from clouds? Reducing black carbon may not be a silver bullet solution many thought according to a new study from NASA. It appears that the net warming effect is more complicated than previously realized. The study concludes that in some climate model studies “the cooling effect due to cloud changes is strong enough to essentially cancel the warming direct effects”. Due to its warming effect, reduction of soot could help cool climate. However, soot absorption also affects cloud distribution, and clouds mostly cool the climate. link

May 2010: Research questions value of cutting black carbon as a global warming solution In recent years, enthusiasm for lowering global emissions of black carbon has increased. But new research published in the journal Geophysical Research Letters suggests that black carbon’s contribution in the climate system is not so straightforward as once thought. While there is little doubt that the fine black particles released from diesel and biomass cook stoves warm the planet by sitting in the atmosphere and absorbing energy, they also affect cloud formation in ways that can create a cooling mechanism, the study says. link 

Around the world

January 2014: Pollution could be 2-3 times worse in India and China than previously thought. A new study has found that global estimates of black carbon emissions in certain areas of India and China could be two to three more times concentrated than previously thought. Black carbon, a major element of soot, is a particle that is generated by the incomplete combustion of fossil fuels, biofuel or biomass. A team of researchers from France and China developed a new model for discerning the amount of black carbon pollution in the air. By mapping regions rather than countries, the study indicated that parts of India and China could have as much as 130% higher black carbon concentrations than shown in standard country models. link

December 2009: New research blames soot for Himalayan warming. Soot coming out from a car’s tailpipes, and not greenhouse gases, could take most of the blame for rapidly melting glaciers in the Himalayas, according to a study led by National Aeronautics and Space Administration. Scientists feared that the black carbon spewed out by industries and cars around the Himalayas might accelerate the melting of the glaciers, which could threaten freshwater resources in the region. There are some parts in the Himalayas that are warming more than five times faster than the global rate. link

October 2009: Soot clouds pose threat to Himalayan glaciers. Glaciers in the Himalayas and the Tibetan plateau that feed the river systems of almost half the world’s people are melting faster because of the effects of clouds of soot from diesel fumes and wood fires, according to scientists in India and China. India and China produce about a third of the world’s black carbon, and both countries have been slow to act. India is the worst. At least in China the state has moved to measure the problem. Decreasing black carbon emissions should be a relatively cheap way to significantly curb global warming. Black carbon falls from the atmosphere after just a couple of weeks, and replacing primitive cooking stoves with modern versions that emit far less soot could quickly end the problem. link 

April 2009. Black carbon may account for as much as half of Arctic warming. The nations of the Arctic Council, including the United States, met in Tromsø, Norway, where action to slow Arctic warming was a major focus. Backed by government ministers and scientists, Al Gore said that soot, also known as “black carbon”, from engines, forest fires and partially burned fuel was collecting in the Arctic where it was creating a haze of pollution that absorbs sunlight and warms the air. It was also being deposited on snow, darkening its surface and reducing the snow’s ability to reflect sunlight back into space. While the chief culprit in global warming is carbon dioxide, recent studies show that black carbon – microscopic airborne particles commonly known as soot – is also a big factor. link 

March 2014: Diesel tractors, bulldozers get cleaned up. While trucks and buses have been cleaned up, it’s taken years longer for farm and construction equipment to keep pace. That’s because these diesel-powered vehicles come in many shapes and sizes, all with different workload demands, and there aren’t always convenient places to slap a filter on their engines. A variety of new technologies are producing cleaner farm and construction machines. Included are lower-sulfur diesel fuel, particle-trapping filters and more efficient engines with fuel-injection software, recirculated exhaust systems or catalysts that prevent pollutants from forming. The new technologies were prompted by the latest U.S. Environmental Protection Agency emission standards, which took hold this year for new, non-road diesel engines used at farms, construction sites and utilities. link

New Jersey is one state showing concern for black carbon. Stopthesoot website explains that diesel emissions contain more than 40 known and probable carcinogens, including fine particulate matter, commonly called soot. Every year, hundreds of New Jerseyans die prematurely and suffer asthma attacks or other debilitating respiratory illnesses from harmful diesel soot. The goal of the Diesel Risk Reduction Program is to reduce the amount of particulate matter emitted by diesel vehicles. Several initiatives including the Diesel Engine Reduction Act of 2005 and the 2007 Highway Rule are already moving big on-road vehicles, such as 18-wheelers, toward drastically lowered black carbon emissions. In fact, the EPA estimates that black carbon emissions will decline 42% from 2001 through 2020, largely because of the diesel rules.

Earthjustice site and video link explaining “soot” – link