2011-02-26 03:19:22Black Carbon
John Hartz
John Hartz

Has the role of black carbon been discussed in SkS rebuttals or blog posts?  

"Unexpected threats to the health of global systems keep emerging. Twenty years ago we didn't recognize global warming. Ten years ago we didn't know about ocean acidification. This might be the landmark week in which a broad public recognized a new threat to the global climate -- black carbon.

"The United Nations Environment Programme (UNEP) has just published a science-based analysis of the climate forcing effects of black carbon. The findings are that cutting black carbon and troposperhic ozone now could halve regional warming for 30 to 60 years and reduce global warming by half a degree. It turns out that reducing black carbon emissions needs to become a priority. According to the United Nations Economic Commission for Europe (UNECE), greenhouse gas reductions alone will not avert further destruction of the arctic; black carbon and ozone reductions are needed."

Source: "The new face of an old enemy" by James Thornton. CEO, ClientEarth, Huffington Post, Feb 25, 2011


Thornton's article would make an excellent cross-post for SkS. 

2011-02-26 03:37:32
Dana Nuccitelli
I touched on it a bit in my Lindzen post.  If we succeed in reducing CO2 emissions, we'll also reduce black carbon emissions.  They both mainly come from burning fossil fuels.
2011-02-26 05:21:52


Well possibly, but there are some exceptions to that rule. One major source of black carbon is Diesel engines.  These can be fitted with Particulate traps, but they would also also require low sulphur Diesel fuel to avoid poisoning the active catalyst coating the trap. Low Sulphur diesel widely used, but less so in developing countries and Marine fuel is very poor quality. 

Low sulphur Diesel has a slightly higher carbon footprint than conventional Diesel.  Particulate traps also increase the exhaust back-pressure slightly which can compromise fuel consumption and carbon dioxide emissions. Note: Diesel engines are not optimised specifically to minimise fuel consumption, but conform to tight particulate and NOx regulations.  Most manufacturers have tried to avoid traps due to durability and cost issues but they are more commonly adopted on buses and some cars.

Targeting black carbon from Diesel engines through traps, coal plants through the use of super critical technology and possibly biomass through specially designed stoves, are among the most cost effective mitigation techniques available.  Imagine a situation where China and the US were given the option to reduce black carbon from coal stations rather than CO2. Perhaps they may have been less hostile to regulations.

The situation with slash and burn is rather more confused, there may be even a short term cooling effect from this.  

I found this short report from NASA particularly interesting.  Almost exactly half the net positive forcing is due to road transport, a rather different result than usually assumed from the naive counting of greenhouse gases! 

The caveat is that some of these non-CO2 effects are more short term, and could be used as an excuse to relax pressure on reducing CO2


2011-02-26 19:27:54


This article emphasises the last point. However something is better than nothing and we need to ensure feedback effects don't kick in. Reducing black carbon might allow that tap to be turned down immediately, reducing CO2 might be to slow.

Scientist's View: In Climate Action, No Shortcuts Around CO2 from Climate Change News Digest

A scientist warns against shifting the climate focus too far from the central challenge, curbing carbon dioxide

2011-02-27 01:32:00A Broader View Needed
John Hartz
John Hartz
Black carbon emissions have multiple negative environmental consequences. Therefore, there are multiplea reasons why black carbon emissions should be reduced.
2011-02-28 10:15:35NY Times DOT Earth: Con
John Hartz
John Hartz

Andy Revkin has now posted a second artilce about the debate between climate scientists aobut the importance of curtialing black carbon and ozone emissions.

In the first article, "Scientist’s View: In Climate Action, No Shortcuts Around CO2" posted on Feb 24, Revkin includes the following comment from Raymond T. Pierrehumbert.

"From the standpoint of improving human welfare, there are compelling reasons to expend resources to reduce soot and ozone pollution, just as there are compelling reasons to expend resources to provide access to clean water, or to reduce illiteracy. But it would be a mistake to view abatement of soot and ozone as a significant part of the effort to combat climate change.

"There are many unresolved questions as to the effects on climate of soot and ozone control actions, but let’s for the moment accept the argument that these effects would be beneficial. It nevertheless remains true that, if one’s goal is to limit climate change, one would always be better off spending the money on immediate reduction of CO2 emissions while deferring action on short lived climate forcings.

"Because the natural CO2 removal processes are so slow, CO2 accumulates in the atmosphere like mercury accumulating in the fat of a fish. If we wind up emitting an extra gigatonne [billion metric tons] of CO2 into the atmosphere this year, it commits the Earth to a certain amount of additional warming that can’t be taken back — a warming that starts to emerge within decades but will still be with us after thousands of years. An extra gigatonne per year of CO2 emissions will cause the atmospheric CO2 to grow by a certain amount each year, year after year.

"Thus, the benefits of a reduction in CO2 emissions — or even a reduction in the emissions growth rate — increase dramatically with time. In contrast, soot and ozone do not accumulate in the atmosphere. They respond primarily to the emissions in any given year, so reducing these emissions only gives a one-time fixed climate benefit.

"Reducing CO2 emissions is like turning down the water faucet filling a bathtub with no drain. The lower you turn the faucet, the longer you have before the bathtub overflows. Reducing soot emissions is like noticing your bathtub is in danger of overflowing, and responding by scooping a cupful of water out of the tub while leaving the hot water faucet going full blast.

"Development of  economically feasible direct air capture of CO2 would allow us to “open up the drain” to some extent, but it would be foolish at this point to count on that being possible. [Link added by Andy R. for context.]

"Every year that action on CO2 emissions is delayed is another year that CO2 emissions continue to grow unabated, and each passing year inexorably ratchets up the warming to which the Earth is committed. In contrast, reducing emissions of a short-lived forcing like soot or methane will have almost exactly the same climate benefit a hundred years from now as it would if done immediately. So, it’s obvious that given a choice, where climate is concerned spending resources on reducing CO2 emissions trumps everything else.

"The UN report itself is quite clear on the imperative for decarbonization, stating “Deep and immediate carbon
dioxide reductions are required to protect long-term climate, as this cannot be achieved by addressing short-lived climate forcers.” The danger in leaning too heavily on climate effects as a justification for soot/carbon mitigation
is that doing so tends to obscure this fundamental truth. When it comes to climate, CO2 is sui generis.

"I go through this argument in more detail in my RealClimate article, “Losing time, not buying time.

"Further information about the way today’s CO2 emissions reset the climate of the next several millennia can be found in the National Research Council Climate Stabilization Targets report, of which I was a co-author:

"Research discussed in that report indicates that, if one adopts the European Union’s threshold for dangerous climate change, then “the bathtub is full” when we have emitted a total of one thousand gigatonnes of carbon (in the form of CO2). We are about halfway there.

"I wish to make it clear that I do think action on ozone/soot is needed. Some of the things one would do to reduce these pollutants would also stimulate investment in the clean energy systems needed to reduce CO2. It’s also probable that soot/ozone reduction would have some direct beneficial effect on regional climate. I’m not arguing against that. I’m arguing for recognition that soot and ozone are knobs that control a very different aspect of climate from the aspect controlled by CO2, and that these very disparate aspects should not in any way be considered equivalent.

"Whatever climate implications soot/ozone control may have, they should be lumped together with the general basket of environmental benefits provided by reductions in soot and ozone, and not viewed as addressing in any way the same issues as posed by CO2. We need to feed the children dinner tonight, and we also need to save for their college education; when money is tight, we naturally tend to do the former, and wonder how in the world we’ll manage to also do the latter. But we don’t argue that doing one substitutes for doing the other."


2011-02-28 10:28:11NY Times DOT Earth: Pro
John Hartz
John Hartz

In Andy Revkin's second article, "A Defense of Acting on Ephemeral Sources of Heat" posted on Feb 27, he includes the following comment from Drew T. Shindell.

"As chair of the UNEP/WMO Integrated Assessment of Black Carbon and Tropospheric Ozone, I would like to point out that our report in fact draws many very similar conclusions about the importance of CO2 to those made by scientists worried that CO2’s primary is under-appreciated. Specifically, in the ‘main messages’ of our Summary for Decisions Makers, we include these three points (excerpted):

1) Reducing black carbon and tropospheric ozone now will slow the rate of climate change within the first half of this century. Climate benefits from reduced ozone are achieved by reducing emissions of some of its precursors, especially methane which is also a powerful greenhouse gas. These short-lived climate forcers – methane, black carbon and ozone – are fundamentally different from longer-lived greenhouse gases, remaining in the atmosphere for only a relatively short time. Deep and immediate carbon dioxide reductions are required to protect long-term climate, as this cannot be achieved by addressing short-lived climate forcers.

2) The identified measures complement but do not replace anticipated carbon dioxide reduction measures.

3) Both near-term and long-term strategies are essential to protect climate . Reductions in near-term warming can be achieved by control of the short-lived climate forcers whereas carbon dioxide emission reductions, beginning now, are required to limit long-term climate change. Implementing both reduction strategies is needed to improve the chances of keeping the Earth’s global mean temperature increase to within the [United Nations Framework Convention on Climate Change] 2 ̊C target.

We do believe that the impact of short-lived forcers is an important part of climate change, however, and that policy-makers should be aware of this. Certainly some people worry that efforts to reduce short-lived pollutants could draw attention and funding away from efforts to reduce CO2. However, it is also possible that nations working together on short-lived pollutant controls could achieve substantial success which might build confidence and ease the path towards agreement on CO2 emissions reductions.

Agreements on short-lived pollutants may be easier to achieve, as historic contributions are not important and so finger-pointing about who’s to blame for how much of the problem is eliminated. Additionally, those areas reducing emissions tend to reap the greatest benefits, so there is an incentive for each country to do its utmost (as opposed to CO2, where all get the same benefit from actions by any country). So efforts to cooperate on short-lived forcers could slow efforts to reduce CO2, but they also might make it easier to deal with.

It is also important to assess the risk of action in comparison with the risk of inaction. Efforts have been underway for decades to reduce CO2 emissions, yet our trajectory remains at or even above the most pessimistic scenarios of 20 years ago. The UNEP/WMO Assessment presents projections showing that we are likely to exceed the 2 ̊C threshold in the 2040s under our current emissions pathway, or even with fairly aggressive CO2 reductions since it takes a long time for plausible scenarios to have a substantial impact.

If we focus exclusively on CO2, there is a real risk of passing 2 ̊C even if we manage to lower CO2 emissions, and if we fail the Earth would face both warming from short-lived and long-lived pollutants. We could reduce short-lived pollutants later, of course, but the inertia from CO2-induced warming means that those measures can only slow the rate of warming, not reverse it and bring us back below 2 ̊C. The combination of reducing short-lived and long-lived forcers has at least a fighting chance of keeping us below 2 ̊C though.

There is also a value judgement inherent in any suggestion that CO2 is the only real forcer that matters or that steps to reduce soot and ozone are ‘almost meaningless’. Based on CO2’s long residence time in the atmosphere, it dominates long-term committed forcing. However, climate changes are already happening and those alive today are feeling the effects now and will continue to feel them during the next few decades, but they will not be around in the 22nd century. These climate changes have significant impacts. When rainfall patterns shift, livelihoods in developing countries can be especially hard hit. I suspect that virtually all farmers in Africa and Asia are more concerned with climate change over the next 40 years than with those after 2050. Of course they worry about the future of their children and their children’s children, but providing for their families now is a higher priority.

Shifts in rainfall are even more closely tied to short-lived forcers, especially black carbon, than is global warming over the near-term, so reducing these forcers provides strong leverage to mitigate these real-world impacts on human well-being. Biological systems are also being affected now. Declines in Arctic sea-ice and warming in high altitude regions can literally push habitable zones for some living things off the face of the planet. In general, the ability of a species to cope with climate change depends on how fast that change takes place. So limiting the near-term rate of climate change may save species from going extinct well before the impact of CO2 reduction is felt. These climate impacts must be weighed against the long-term impacts of CO2. I would tend to agree with those concerned primarily about CO2 that the long-term effects may be the most important for climate.

It’s fundamentally scary to think about something dangerous that lasts thousands of years in the atmosphere. Think of nuclear waste – would it really be so frightening if it was as dangerous but only lasted a few weeks? However, saying CO2 is the only thing that matters implies that the near-term climate impacts I’ve just outlined have no value at all, which I don’t agree with. What’s really meant in a comment like “if one’s goal is to limit climate change, one would always be better off spending the money on immediate reduction of CO2 emissions’ is ‘if one’s goal is limiting LONG-TERM climate change”. That’s a worthwhile goal, but not the only goal.

And of course there are enormous benefits to human and ecosystem health through improved air quality if black carbon, carbon monoxide and methane are reduced, which are quantified in the Assessment. So we have two things that are worth doing – controlling short-lived forcers and controlling long-lived forcers. Over the long-term, yes, the short-lived are a small piece of the pie like the tiny budget programs that are politically “touchable”. From a near-term perspective, however, the short-lived forcers are the only real lever we have, and near-term climate change matters too. And the two in combination seem to be about the only plausible way forward to meeting the world’s 2 ̊C target.

So rather than set one against the other, I’d view this as analogous to research on childhood leukemia versus Alzheimer’s. If you’re an advocate for child’s health, you may care more about the former, and if you’re a retiree you might care more about the latter. One could argue about which is most worthy based on number of cases, years of life lost, etc., but in the end it’s clear that both diseases are worth combating and any ranking of one over the other is a value judgement. Similarly, there is no scientific basis on which to decide which impacts of climate change are most important, and we can only conclude that both controls are worthwhile. The UNEP/WMO Assessment provides clear information on the benefits of short-lived forcer reductions so that decision-makers, and society at large, can decide how best to use limited resources."


2011-02-28 10:33:50Synthesis View
John Hartz
John Hartz

In Andy Revkin's second article, "A Defense of Acting on Ephemeral Sources of Heat" posted on Feb 27, he concludes with the following:

Ken Caldeira, who studies climate, carbon and energy at Stanford University and the Carnegie Institution, sent a really nice synthesis view on CO2 and other greenhouse substances worth appending here:

If carbon dioxide and other long-lived greenhouse gases were not building up in the atmosphere, we would not be particularly worried about the climate effect from the short-lived gases and aerosols. We are concerned about the effect of methane and black carbon primarily because they are exacerbating the threats posed by carbon dioxide.

If we eliminated emissions of methane and black carbon, but did nothing about carbon dioxide we would have delayed but not significantly reduced long-term threats posed by climate change. In contrast, if we eliminated carbon dioxide emissions but did nothing about methane and black carbon emissions, threats posed by long-term climate change would be markedly reduced.

While this issue of addressing long-lived vs. short-lived drivers of climate change is often posed as a dichotomy, there is a unifying perspective:

If we are to live on this planet for the long haul without transforming it into what seems like an entirely different planet, we will need to come to the understanding that we can no longer use the atmosphere as a dumping ground for the waste products of modern industrial civilization.

The scale of our civilization has simply become too large relative to the scale of our atmosphere to go on considering the atmosphere to be effectively infinite.

As a society, we need to reconceptualize our relationship to the atmosphere. From that reconceptualization, a whole range of policy implications will emerge.

Once we adopt the perspective that it is unacceptable to use the atmosphere as a sewer, we will address issues related to all sorts of emissions: sulfur, black carbon, methane, carbon dioxide, etc.



PS. I am reminded of Tom Lehrer’s comment about life: Life is like a sewer. What you get out of it depends on what you put into it.

Caldeira’s conclusions about carbon dioxide, as well as those of Pierrehumbert and Susan Solomon, among others, are one reason for their support of intensified research on directly removing CO2 from the atmosphere (as reflected in a 2010 paper by Cao and Caldeira).


2011-02-28 10:57:37Raymond T. Pierrehumbert.
John Hartz
John Hartz

Raymond T. Pierrehumbert has posted on the comment thread to Revkin's second article.