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Black carbon is a much larger cause of climate change than previously assessed; about twice previous estimates, and 2/3 the effect of CO2

Schematic overview of the primary black-carbon emission sources and the processes that control the distribution of black carbon in the atmosphere and determine its role in the climate system. Source: Bond et al. Click to enlarge.

Black carbon (BC) is the second largest man-made contributor to global warming and its influence on climate has been greatly underestimated, according to the first quantitative and comprehensive analysis of this pollutant’s climate impact.

The direct influence of black carbon, or soot, on warming the climate could be about twice previous estimates, according to an in-depth open-access study by an international team of 31 authors published in the Journal of Geophysical Research-Atmospheres, a publication of the American Geophysical Union. Accounting for all of the ways black carbon can affect climate, it is believed to have a warming effect of about 1.1 Watts per square meter (W/m2), or approximately two-thirds of the effect of the largest man-made contributor to global warming—carbon dioxide.

Emission rates of BC in the year 2000 by region, indicating major source categories in each region. Source: Bond et al. Click to enlarge.

Black carbon aerosol plays a unique and important role in Earth’s climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption, influence on liquid, mixed-phase, and ice clouds, and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations.

Predominant sources are combustion related; namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr-1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models, and should be increased by a factor of almost three.

...Our best estimate of black carbon forcing ranks it as the second most important individual climate-warming agent after carbon dioxide, with a total climate forcing of +1.1 W m-2 (+0.17 to +2.1 W m-2 range). This forcing estimate includes direct effects, cloud effects, and snow and ice effects. The best estimate of forcing is greater than the best estimate of indirect plus direct forcing of methane. The large uncertainty derives principally from the indirect climate-forcing effects associated with the interactions of black carbon with cloud processes.

—Bond et al.

The authors of the study organized their major findings into twelve areas:

  1. Black carbon properties.
  2. Black carbon emissions and abundance
  3. Synthesis of black carbon climate forcing terms
  4. Black-carbon direct radiative forcing
  5. Black carbon cloud effects
  6. Black carbon snow and ice effects
  7. Impacts of black-carbon climate forcing
  8. Net climate forcing by black-carbon-rich source categories
  9. Major factors in forcing uncertainty
  10. Climate metrics for black carbon emissions
  11. Perspective on mitigation options for black carbone emissions
  12. Policy implications

Comment on the paper from the JGR-A editors
In a special comment on the significance of the Bond et al. paper, the editors of the Journal of Geophysical Research - Atmospheres noted that:
This comprehensive effort by a team of leading scientists from various complimentary disciplines provides an unprecedented review and assessment of the current state of the science and an impressive effort to quantify the role of black carbon in the climate system...The result is the most up-to-date assessment of the science of black carbon with new insights and recommendations for future research.
The JGR-Atmospheres Editors decided to provide a platform for this article because we believe that there is great scientific value in reviewing, assessing, and synthesizing a large body of existing literature, and by going beyond the conclusions that any individual paper can reach.
This paper will be of interest to the community and will focus the discussions and future research into black carbon and its importance.

The study, a four-year, 232-page effort, led by the International Global Atmospheric Chemistry (IGAC) Project, is likely to guide research efforts, climate modeling, and policy for years to come, the authors and other scientists familiar with the paper said.

The report’s best estimate of direct climate influence by black carbon is about a factor of two higher than most previous work. This includes the estimates in the 2007 Intergovernmental Panel on Climate Change (IPCC) Assessment, which were based on the best available evidence and analysis at that time.

Scientists have spent the years since the last IPCC assessment improving estimates, but the new assessment notes that emissions in some regions are probably higher than estimated. This is consistent with other research that also hinted at significant under-estimates in some regions’ black carbon emissions.

The results indicate that there may be a greater potential to curb warming by reducing black carbon emissions than previously thought.

There are exciting opportunities to cool climate by reducing soot emissions but it is not straightforward. Reducing emissions from diesel engines and domestic wood and coal fires is a no-brainer, as there are tandem health and climate benefits. If we did everything we could to reduce these emissions we could buy ourselves up to half a degree (Celsius) less warming—or a couple of decades of respite.

—co-author Professor Piers Forster from the University of Leeds’s School of Earth and Environment in the United Kingdom

However, the international team urges caution because the role of black carbon in climate change is complex.

Black carbon influences climate in many ways, both directly and indirectly, and all of these effects must be considered jointly.

—co-lead author Sarah Doherty of the University of Washington in Seattle

The dark particles absorb incoming and scattered heat from the sun (called solar radiation), they can promote the formation of clouds that can have either cooling or warming impact, and they can fall on the surface of snow and ice, promoting warming and increasing melting. In addition, many sources of black carbon also emit other particles that provide a cooling effect, counteracting black carbon.

The research team quantified the complexities of black carbon and the impacts of co-emitted pollutants for different sources, taking into account uncertainties in measurements and calculations. The study suggests mitigation of black carbon emissions for climate benefits must consider all emissions from each source and their complex influences on climate.

Based on the scientists’ analyses of these different sources, black carbon emission reductions targeting diesel engines and some types of wood and coal burning in small household burners would have an immediate cooling impact.

Black carbon is a significant cause of the rapid warming in the Northern Hemisphere at mid- to high-latitudes, including the northern United States, Canada, northern Europe and northern Asia, according to the report. The particles’ impacts can also be felt farther south, inducing changes in rainfall patterns from the Asian Monsoon. Curbing black carbon emissions could therefore have significant impact on reducing regional climate change while having a positive impact on human health by reducing the amount of damage the particles cause to the respiratory and cardiovascular systems.

Policy makers, like the Climate and Clean Air Coalition, are talking about ways to slow global warming by reducing black carbon emissions. This study shows that this is a viable option for some black carbon sources and since black carbon is short-lived, the impacts would be noticed immediately. Mitigating black carbon is good for curbing short-term climate change, but to really solve the long-term climate problem, carbon dioxide emissions must also be reduced.

—co-lead author Tami Bond of the University of Illinois at Urbana-Champaign


  • Bond et al. (2013) Bounding the role of black carbon in the climate system: A scientific assessment. Journal of Geophysical Research-Atmospheres doi: 10.1002/jgrd.50171



Well better move the effort into reducing black carbon rather than CO2.
So work on diesel filters (ongoing) and cleaning up stoves + kerosene lamps in the developing world.

This is a much more solvable problem than reducing CO2 as black carbon is a by product of many processes, rather than the main exhaust gas.

You also have to stop people burning down forests (or you have yet another reason to do this) and burning off crops, and clean up coal power stations.


It would be easier to take this paper seriously if the editors of the Journal of Geophysical Research knew the difference between complementary and complimentary. Editors? Really?
And I don't doubt that carbon black is a larger factor than previously thought, just that somebody ought to at least look at JGR-A's comments before they submit them.
Next thing you know they will be mixing up loose and lose.

Richard C Burton

so does anybody know of how to lessen black carbon from a woodstove. Myself and alot of others use woodheat during the winter-I assume choking it down at night greatly increases black carbon even if it's an EPA stove-any practical retrofit filters out there??? suggestions?


It would be a lot more believable if after their "studies", they could agree on an effect within 100% + or -.

I note that the most heavily industrialized continent, North America, is also the lowest emitter of "black carbon" whatever that really is.

The figures also date from a decade ago, and I assume that North American emissions have declined markedly since then, just as CO2 emissions from North America have declined, over the decade.

Therefore, the appropriate solution is to industrialize the poorer areas of the World. Not go back to the caves, as so many Greens advocate.

I'm sorry but this reeks of finding a so-called "issue-problem" that seeks to provide support for a failing "problem" of CAGW. The worst continents are using the same primitive technology that mankind has employed for thousands of years, without apparent harm.


Burning wood for heating and cooking was OK a few hundred or thousand years ago because the world population was very small and there were no coal powered polluting e-plants, no cement plants, no ICE vehicles, planes, ships, heavy machinery, diesel locomotives, war machines, sport machine,etc etc.

If we lived as they did a few thousand years ago, I doubt that we would have the level of air pollution that we have today. Plagues and various diseases and gang wars would keep population (and pollution) low.


One of the ugly aspects of carbon black is the ubiquitous nature of the its sources. I was hiking in Nepal in a completely agricultural area and the only time you saw a bit of clear sky was at dawn, within half an hour of dawn the sky was full of wood smoke. And this to the point of you wondering where in the denuded world these people were finding wood to burn. The government was encouraging them to use natural gas/propane stoves but wood gathered by a kid is free, so you can imagine how the new stoves went over.
Then there are peat fires and subterranean coal fires to account for, and manufacturing processes, energy production and transportation...
Talk about a plethora of targets for reductions, though.
But don't even think you can touch my pellet stove or bother my rotisserie chicken place!


When you only have 5 bucks you have to use whatever you can pick up to cook with and heat your home.. Most often its fast growing brush and scrub and dried dung and clumps of peat and sticks and even leaves if need be.

And on top of this remember europe ...greened... up using diesel before they had soort catchers... so ALOT of soot came from europe. Now alot of it is comming from developing world where even cars are run on wood sometimes.


Is trying to discipline 8,000,000,000 people rather futile?

The one child per couple as applied in China may be one of the best way to slow population (and pollution) growth. Otherwise, the globe may have 16B people sooner than expected and many problems will become unsolvable?

OTOH, another BWB or two may reduce economic growth so much that population and pollution growth would eventually go down?


@ Richard C Burton.
There is in fact a increasing number of means to extract soot from exhaust fumes. Largely four categories: washing with water curtain, ionization, vortex and condensation heat exchange where particles stick to humid surfaces.
To be straightforward you will upgrade to a heat-power device
that is fully automated and accessible with a phone-app.
The ol' chimney still depends on proper handling. That is - give it time to heat up, always have a nice flame to fully burn the wood.
For closed stoves burning above 2000 degrees f with an insulated chamber will break up all atomic bonds.


China know their issue with their overuse of coal plants. That is why they have started researching into Thorium powered Molten Salt Reactors.

Even they have constraints having to deal with their own power industry's political influence. If all goes well they may have something to deploy by 2025.

Kit P

“so does anybody know of how to lessen black carbon from a woodstove. ”

It is easy and cheap. A room temperature thermostat opens and closes a damper allowing the wood stove to either run hot or get just enough air to keep embers smoldering. I also recommend a smaller stove and just using it when it runs all the time with the bedroom doors closed.

“China know their issue with their overuse of coal plants. ”

There is no evidence of this. They have learned they can not produce enough coal so they have to import it. It is not until that happened in about 2005 that they got serious about nuclear.

“That is why they have started researching into Thorium powered Molten Salt Reactors. ”

They have started a massive LWR building program. The US is the world leader in making power with nukes. We do it with LWR with 5% enriched uranium. Those who teach like Thorium powered Molten Salt Reactors

Electrification is the route to improving air quality since it is easier to regulate one coal-based power plant than a million point sources. All electric-houses have lower indoor air pollution too. The reason that the US has lower soot is that regulated burning of coal and biomass is very clean and efficient. Cleaner wood stoves have been around to 30 years. Agricultural burning has been reduced to cases where there is not an alternative. Then there is 104 nu7ke plants that produce 20% of our power.


When it comes to climate change - there are the facts, and when there is the reporting:


Yes KitP there are ways to reduce black carbon and other harmful emissions. More electrification is probably the best way to go as long as your electricity is produced without emissions. Our home (like the majority in our area) is 100% electric.

Wood stoves and fire places were very popular a few decades ago but many cities are currently restricting their use with the support of the majority. Improved Electric fire places are replacing them. We converted ours in 1996 but I must admit that we use the cold weather heat pump most of the time for hea

Richard C Burton

@ds; can you steer me towards more information re how to treat the smoke coming out of my woodstove? thanks
@KitP; unfortunately when one chokes down a woodstove to make it run thru the night, it's basically smouldering and I'm sure polluting like crazy...and I would think that would be so regardless if it is an EPA approved stove-and I hear you that it's best to run a smaller stove with full air rather than choke down a bigger one.

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