News Section
Stories from Climate Central's Science Journalists and Content Partners

Black Carbon Second Only to CO2 in Heating the Planet

No discussion of climate change can get very far without focusing on greenhouse gases — pollutants including carbon dioxide, methane, nitrous oxides and more, which are trapping heat and driving the planet’s temperature upward.

But according to a report published Tuesday in the Journal of Geophysical Research: Atmospheres, the second most important heat-trapping pollutant isn’t a gas at all: it’s black carbon, more commonly known as plain old soot, generated mostly from the burning of diesel fuel, coal and woody plant material. “There’s a relatively small amount in the atmosphere,” said the study’s lead author, Tami Bond, of the University of Illinois at Urbana-Champaign, in an interview. “But it’s very powerful.”

New research says the second most important heat-trapping pollutant isn’t a gas at all: it’s black carbon, generated mostly from the burning of diesel fuel, coal and woody plant material.
Credit: A6U571N/flickr.

This isn’t the first hint that black carbon might have an outsize effect on climate. Research published in 2008, for example, concluded that black carbon’s global-warming effect was about twice as great as the Intergovernmental Panel on Climate Change’s major report in 2007 had estimated — the same conclusion reached in the new study — but that conclusion wasn’t considered definitive.

Even so, scientists and policymakers understood that reducing emissions of black carbon could be a relatively quick and easy way to slow the pace of global warming, and a number of initiatives including one created by the U.S. and another by the United Nations have been created to try and deal with the problem. The particles can also cause or aggravate lung disease, so there’s a public-health benefit to reducing emissions as well.

But without a true sense of how big an issue black carbon really was, scientists and policymakers couldn’t make truly informed decisions about how to attack it. So Bond and 30 other scientists launched a truly comprehensive assessment, coordinated by the International Global Atmospheric Chemistry Project, of how much black carbon there really is in the atmosphere, where it comes from and how much it warms the planet.

According to the lead author of the study, reducing emissions from diesel engines is the biggest priority, followed by some kinds of wood and coal burning in homes — for cooking, and maybe for heating.
Credit: wmshc_kiwi/flickr.

In the end, the study took four years. “It wasn’t supposed to take that long, but the science isn’t entirely straightforward,” Bond said. On the most basic level, black carbon contributes to global warming simply because it’s black. “The particles absorb just about every ray of light that hits them,” she said, heating up like dark clothing on a sunny summer day and warming the air around them. In the Arctic, black carbon particles eventually settle onto ice and snow, where they help speed melting.

Particles of black carbon come in different sizes, however, and in some cases they’re small enough that they can affect cloud formation — in some cases, at least, helping to create clouds that reflect sunlight. Some sources of black carbon, moreover, such as the open burning of plant waste, generate other kinds of particles that tend to cool the planet. “If we shut those sources off, you could actually make the warming worse,” Bond said.

The new report tries to take all of these complexities into account. “It’s clear that reducing emissions from diesel engines is the biggest priority, followed by some kinds of wood and coal burning in homes — for cooking, and maybe for heating,” Bond said. 

Emissions from some kinds of small industry might also be a target, but not from all. “We tried to estimate the net effect of each source, along with the uncertainties in our estimates,” Bond said. “In some cases, the uncertainty is so large that it’s clear we need more understanding.”

Nevertheless, Bond said reducing the most clearly harmful sources of emissions is something we already know how to do. “Black carbon was really high in the U.S. in the early 1900s,” she said. “Since then, we’ve increased our use of fossil fuels dramatically without increasing those emissions. This is not rocket science.”

The black carbon study may not have all the details nailed down, and it doesn’t do away with the thornier, longer-term issue of carbon dioxide emissions. But it does point to a way to slow the pace global warming significantly and quickly. Given that the dire effects of warming are showing everywhere — as a new report makes clearer than ever — this could prove invaluable as a guide to effective policy. 

Related Content
Groundbreaking New Study Shows How to Reduce Near-Term Global Warming
U.S. Launches Multinational Clean Cookstoves Initiative
5 Must-See Charts From Major New U.S. Climate Report

Comments

By Tom
on January 15th, 2013

Its called ‘ca’rbon black’  not ‘black carbon’.  While much of what you say above sounds reasonable, that’ you’re unaware of the proper name makes me want to double check the rest of the article.

Reply to this comment

By Mike Lemonick (Princeton, NJ 08542)
on January 15th, 2013

Tom:

The title of the paper is “Bounding the role of black carbon in the climate system: A scientific assessment,” so unless the 31 eminent scientists who spend four years working on this report are wrong and you’re right—which seems kind of dubious, don’t you think?—I’ll just stick with what we’ve got.

Reply to this comment

By Lewis Cleverdon
on January 15th, 2013

Michael - please could you clarify the relevance of black carbon numerically ? As in, what percentage of present realized warming it causes compared to CO2 ?

For the report to put wood-burning stoves alongside diesel engines seems bizarre - even with both having first rate soot controls, the latter is still emitting its full quota of fossil carbon, making it dozens of times more culpable for warming, while the former needs only decent forestry practice (coppice harvest cycling building soil carbon) to be marginally carbon negative. If the billions of people dependent on wood for heating and cooking switch to fossil fuels, then our chances of resolving AGW are decimated.

The claim of the ‘open burning of plant waste’ such as in wildfires having a net cooling effect is also news to me. Biomass contains only a tiny percentage of sulphur and with rising wildfire temperatures there are presumably increasing volumes of nitrogen being oxidized, providing a highly potent very long-lived GHG. Does the report actually give a full spectrum assessment of such fires’ emissions culpability ?

I’m chary of the notion of cleaning up soot outputs as a means of ‘buying time’ for ending fossil fuel dependence - anything that diverts from the urgency of the latter priority ain’t necessarily helpful. As an alternative course of action it is plainly harmful, meaning that it surely needs to be seen as a useful ancillary option to ending fossil fuel combustion ?

Regards,

Lewis

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on January 15th, 2013

Black carbon has been branded as the no 2 bad actor for a while now. There has been a lot of work into black carbon. IMO, the here referenced US Govt. initiative is also actually fairly weak and not the best example of action in this area.  For instance, not mentioned here is the pioneering work of Ramanathan (there were others too of course) at the Scripps Institute on this which led to Project Surya: http://www.projectsurya.org/  He however is not one of the authors of this particular article. Apparently China and India account for about a third of global black carbon emissions. For instance see: Black Carbon Research Initiative, National Carbonaceous Aerosols Programme (NCAP) Science Plan, INCCA: Indian Network For Climate Change Assessment, March 2011:  http://moef.nic.in/downloads/public-information/Black Carbon Research Initiative.pdf

Reducing BC emissions is the low hanging fruit of mitigation initiatives. It is a no brainer. Black carbon settles out of the atmosphere relatively quickly and significant emissions reductions can potentially be achieved through relatively painless changes in behavior.  However, CO2 is the main problem not only because it provides the most forcing of all of the anthropogenic emissions in terms of outright magnitude but also because it persists in the atmosphere for so very long (centuries to millennia).

And BTW, ML like all of us does make mistakes but this isn’t one of them Tom. It’s black carbon. Carbon black is something else entirely.

Reply to this comment

By Mike (Seattle, WA 98105)
on January 15th, 2013

Tom:
Black Carbon is an accepted term among scientists. Look it up.

Reply to this comment

By Mike (Seattle, WA 98105)
on January 15th, 2013

There are also short-term reasons for reducing soot.
Anyone who has ever lived downwind from a wood fireplace can attest to how much of a problem wood smoke can be, from annoying to hazardous.
Visits to emergency rooms for asthma attacks go up along with levels of wood smoke in a region.

Reply to this comment

By Dave
on January 15th, 2013

@Lewis:

You addressed ML but do you mind if I chime in too…  I think it’s an important topic and you raised some interesting points.

1. “If the billions of people dependent on wood for heating and cooking switch to fossil fuels, then our chances of resolving AGW are decimated.”  I don’t know about that. I think the math could go both ways. I do know that the Project Surya approach is to improve the efficiency of cooking stoves – not switch to fossil fuels.  Maybe that project is concluded or nearing conclusion.  You get BC emissions from incomplete combustion.  I’ve also heard of some use of solar stoves for cooking for families and villages. Lots of people in Africa and Asia use cow dung for cooking and heating and that’s another major culprit re BC. Apparently, overall non diesel BC emissions are quite significant although diesel combustion is the biggest source making it a double climate whammy when you count in the CO2 as well. Let’s also not forget the current health issues related to dense atmospheric BC.

2. Re the numerical relationship between CO2 and BC in terms of net GW contribution, I vaguely recall an estimate that it’s somewhere in the region of half that of CO2 in terms of current forcing in W/m2. 

3. To your wariness about BC as a means to mitigate climate change – perhaps that relates more to your perception of politics or psychology.  Logically, not pursuing BC reductions as part of a global strategy to reduce GW makes no technical sense.

Reply to this comment

By Lewis Cleverdon
on January 17th, 2013

Dave - thanks for your response.

I’d well agree that failing to pursue BC reductions as part of a global strategy to reduce GW makes no technical sense. One concern I have with this report is its implication that BC cuts could stand as an alternative “for a couple of decades” to phasing out fossil fuels. This may not have been the authors’ intention, but there are clearly plenty of interests ready for such a message.

Another concern is that there is there is a vituperative and growing lobby against the harvesting of forestry for energy (including sustainable coppice forestry as we’ve used for several millennia) who will feed on this report and again bend it to their own ends. Alongside them is a shady lobby that seeks to blame developing nations for the problem of excess carbon, (they even burn cow dung you know) for whom a biomass BC focus is a gift.

Another concern is that the authors assume that their (unquestioned) scientific expertise gives a greater authority to their recommendations of strategy for political action - when in fact the international politics of climate is a subset of international relations, which is a highly subtle field of study in its own right, and in which the authors have no published standing at all that I know of. (I of course stand ready to be corrected if any of them have).

Given the obstruction of international agreement since 2000, it is hard to see why a BC focus should be expected to make a difference. It has been available as an option since discussions in the ‘90s, to no avail. Similarly, if the superpowers had wanted to mitigate the GW problem without cutting FF usage, they could readily have agreed the use of native afforestation for biochar sequestration as a means for all nations to verifiably recover their ‘historic’ carbon emissions during this century. This would also have ended the major block on negotiations that the cumulative outputs issue imposes. This far more productive and seminal option has again been ignored since the ‘90s.

With negotiations now heading for a comprehensive agreement in 2015, just about the last thing needed is a shift away from the accepted CO2e focus (i.e. all GHGs measured by their equivalent CO2 GW potential) into a disparate set of sub-negotiations over controls on individual GHGs, such as BC, “because some are easier to do”. This misunderstands the serious progress made in the negotiations before Cheyney slammed on the brakes.

Before making proposals of a novel strategy of climate action, the question needs asking just why the AGW problem, with its clearly existential risks, has been allowed to fester and multiply for 20 years, or at least for the 12 years since Cheyney took office. The received wisdom (its the fossil lobby) should not satisfy any scientist or inquiring mind, given the general silence and lack of counter-measures across all US corporations, all of whom are in the climate firing line and few of whom have any inherent loyalty to fossil fuels. Moreover, not only does the European fossil lobby refrain from funding denialism and from blocking legislation like its US counterparts, but also major European corporations have been getting candid in their demands for commensurate collective global action (e.g. Munich Re, Price-Waterhouse-Cooper, etc).

Another telling pointer is the speed with which the circus of denial was fabricated during 2009, with its influence since being claimed, unofficially but very widely, as the excuse for Obama’s declining interest in climate. That change began with his switch from:
- adamant support for urgent action (after being elected in his November 2008 speech to the “Governors’ Climate Summit”)
- to adopting Bush’s unilateral 2005 emissions baseline in March 2009 and reneging on the agreed 1990 UNFCCC baseline, thereby sending the clear signal around the international community that US policy would be maintained.

Thereafter, the term ‘climate’ simply fell out of POTUS vocabulary, and his conduct became obstructive, such as in crushing Copenhagen with an untenable ‘deal’ (each American should have three times the emission rights of each Chinese in 2050 ???) and the serial de-railing of the senate climate bill (see Ryan Lizza’s forensic New Yorker article, “While the world burns”). More recently his occasional lip-service on the issue has included both Hype-the-controversies and Strawman prevarications, as well as outright falsehoods. (See his brief statement to the press conference after the election for how many you can spot).

This is not an ad hominem against Obama - I don’t suggest he’s at all corrupt. I suggest that he is merely serving a covert policy (every govt. has them) of a brinkmanship of inaction against China, America’s rival for global economic dominance, and that he inherited the policy after taking office. With the maintenance of global economic dominance having been Washington’s paramount policy priority since WW2, Obama has maintained Cheyney’s stance of not setting up any countermeasures to China’s rise other than the obstruction of global mitigation of GW. (Contrast that with US v USSR). This stance will face China’s govt. with climatic destabilization via crop-failures and food shortages (within 10 to 15 years according to the recent Leeds Uni report) and could put an end to China’s bid for dominance. In this we have the ‘rational’ objective of the US bipartisan policy of a brinkmanship of inaction.

Proposals for novel mitigation strategies need to factor in the superpowers’ priorities if they are to be helpful. In particular, it is worth noting that the received wisdom on climate change in 2000 when Cheyney launched the policy was way off the mark. The standard ideas that developing nations, like China, would face far worse climate impacts than America, and that America would be far better able to afford the damages and rising food costs than China, have proven dead wrong. America is being hit much harder than any equivalent area (says Munich Re data) and its economy is in turmoil while its debt worsens. In this sense, while Obama will avoid saying anything to encourage premature public demand for climate action, with the Jetstream increasingly disrupted there has to be a recognition within the establishment that the bipartisan policy of a brinkmanship of inaction is now unsustainable and even downright counter-productive. Its author, Cheyney, has notable form in this regard.

On balance, I’d not be that surprised if the US conduct of negotiations cautiously shifts to a more productive approach before 2015. US reps at Kyoto spoke respectfully of the future relevance of the climate policy framework of “Contraction & Convergence”, that now forms the basis of most major nations’ negotiating stance (de facto or de jure) and the contention over historic emissions is readily resolved - Indeed, that commitment to a global Carbon Recovery program is clearly an essential part of a commensurate treaty. The open question is whether, faced with a universal deal that meets the Byrd-Hagel resolution demanding universality, the GOP can find a way to un-paint the corner it’s been painting itself into.

Finally, I should just add that I’m all for efforts to cut BC as part of the overall effort. To this end I’ve supported the development of efficient affordable wood-stoves over the years, and am currently working on a low-tech respectably-efficient charcoal retort, that is aimed to give about seven times the 5% yield of the widespread “tin-sheet & a pit” technology, as well as minimizing the GHG outputs.

Regards,

Lewis

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on January 17th, 2013

@Lewis:

Politics and black carbon.  A grimy mixture indeed. smile

Thanks for all that. Good luck with your project.

Reply to this comment

By Nancy
on December 29th, 2013

As others have pointed out, carbon black and black carbon (formerly known as soot) are different things: http://www.ncbi.nlm.nih.gov/pubmed/11331994

Reply to this comment

Name (required):
Email (required):
City/State/Zip:
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.