The biggest source of mistakes: C vs. CO2

Probably the biggest source of confusion and errors in climate discussions concerns “carbon” versus “carbon dioxide.” I was reminded of this last week when I saw an analysis done for a major environmental group that confused the two and hence was wrong by a large factor (3.67). The paragraph I usually include in my writing:

Some people use carbon rather than carbon dioxide as a metric. The fraction of carbon in carbon dioxide is the ratio of their weights. The atomic weight of carbon is 12 atomic mass units, while the weight of carbon dioxide is 44, because it includes two oxygen atoms that each weigh 16. So, to switch from one to the other, use the formula: One ton of carbon equals 44/12 = 11/3 = 3.67 tons of carbon dioxide. Thus 11 tons of carbon dioxide equals 3 tons of carbon, and a price of $30 per ton of carbon dioxide equals a price of $110 per ton of carbon.

I confess that in my books I have tried to consistently use CO2, for clarity’s sake, but have failed to embrace that strategy in the blog. I now realize that was a mistake after receiving an e-mail from a long time a reader who was confused as to whether the price I quoted in a recent post was dollars per ton of carbon or carbon dioxide (even though I had said in the post it was “the price of carbon”).

The reason this confusion arises so much is that scientists usually use carbon, because they are studying the carbon cycle, and governments also usually use carbon, because the scientists do. But “carbon” is not intuitive, whereas carbon dioxide is what we all emit — that is why businesses and the public typically report numbers in terms of carbon dioxide. “Point Carbon” for instance, reports prices in the European market for CO2 allowances (in euros, of course).

And, indeed, the central climate number in this whole area is the atmospheric concentration of carbon dioxide. The media is typically caught in between, sometimes using one and sometimes using the other, and sometimes making a mistake or not being clear.

So I am going to try to be consistent and use CO2. Where relevant I will also include one conversion to carbon, too, without bombarding you with too many numbers. So hopefully, from now on, if I fail to be clear, you should make the default assumption I am talking carbon dioxide.

I would recommend all blogs and journalists clearly state their “carbon dioxide policy” — and be sure to check when reporting on studies or articles or business action that they know whether they are talking carbon or carbon dioxide.


15 Responses to The biggest source of mistakes: C vs. CO2

  1. tidal says:

    This is more a question of why you, Joe, prefer CO2 over C. (Obviously, I am more interested in just getting an effective pricing architecture in place, soon, regardless of whether the metric is CO2 or carbon. But I am not really educated on why CO2 is the “better” metric.)

    We operate under the principal of conservation of mass. I know that is stating the obvious, but doesn’t it have some implications w.r.t. pricing C versus CO2? The process of extracting hydrocarbons for combustion, for instance, is to some extent a removal of carbon from the “inactive cycle” and introducing it into the active cycle. The fact that it “becomes” CO2 is just the physics and chemistry of combustion. The relative “amount” of CO2 is largely determined by the ratio of C:H in the particular fuel (I know I am oversimplifying… but it is still a good approximation.).

    If you accept this, aren’t you are more likely to consider putting the price on carbon at the source, and perhaps more specifically carbon from the “inactive” cycle (i.e. the “naturally sequestered” stores in coal, oil, etc.). Cleaner hydrocarbons (lower C:H ratio) would attract less of a price (e.g. natural gas). “Credits” would only be earned if you could clearly demonstrate that you were somehow removing *carbon* from the “active cycle” and restoring it relatively permanently to the “inactive cycle”.

    For instance, I was reading an interview that Tim Flannery gave regarding Terra Preta, which is basically the burning of organic waste in the absence of oxygen, to create charcoal and hydrogen-rich gases. The charcoal is then buried deep in soil and apparently stays locked out of the active carbon cycle for perhaps thousands of years. Let’s *suppose* this “technology” actually proves effective in sequestering carbon. How would you “credit” the charcoal? By estimating the CO2 that was pulled out of the atmosphere? Or just credit the carbon that gets buried? How would we “equate” the biochar with underground geosequestration of CO2?

    I know that I didn’t touch on agricultural CO2, or deforestation, which are not “inactive” sources of carbon, but even there isn’t it really an issue of oxidizing C to create CO2?

    This is not my area of expertise. Maybe it is really “six of one, half dozen of the other issue” (or 3.67 of 1, one of the other! :) ). But if you have a paragraph or two, or a link, on why you prefer CO2, I would enjoy reading it. Best regards, and thanks for all your excellent efforts and contributions.

  2. Joe says:

    Carbon dioxide is what consumers and businesses generate. I have never met people who think in terms of carbon, other than scientists, and I’m sure that the scientists reading this blog can do the conversion in their heads :)

    I do think that switching back and forth between the two is confusing to most people, so I think that someone who talks or writes regularly on this issue should pick one. Relatedly, I think you are less likely to make a mistake if you 1) consciously stick with one and 2) be sure when you are interviewing people that you asking them which one they are using.

    Finally, if the public needs to better understand one concept, it is probably that CO2 concentrations will keep rising even if we freeze emissions. So I think it best to focus on CO2.

    That said, I will try to remember to do the conversion once in each post when it comes up.

  3. David B. Benson says:

    Joe — The trouble with that policy is that it leaves out methane and black carbon, “soot”.

    tidal — Pyrolysis does not make Terra Preta, a uniquely Amazonian soil type. It makes biochar. If the goal is to permanently sequester carbon in the ground, making biocoal is far better. See my comments on previous threads.

  4. Scatter says:

    Yes can we get rid of C please? Much better to talk about CO2 as that’s what is dealt with 99% of the time and the concept of C when you’re talking about actual CO2 emissions is a very difficult thing to communicate.

    In the UK things seem to be slowly switching over to CO2 but there’s still policy wonks and the like who only think in C.

  5. Tom says:

    Part of the problem is the fascination with carbon footprints and carbon offsets. Most people haven’t a clue what the price of carbon is and whether it relates to carbon dioxide or carbon. What matters most is the context. How much are prices rising or falling and what impact will it have on behavior and investment.

    That said, carbon dioxide should be the standard.

  6. Paul K says:

    Most of the carbon I buy is in the form of gasoline. How many gallons of gasoline must be burnt to yield a ton of CO2. If I knew the answer, I would know my current cost and be much better able to consider the ramifications of the pricing advocated here.

  7. Pangolin says:

    Why I prefer carbon.

    If I am going to demonstrate to somebody, say in an booth, the relative environmental cost of burning fuels I can have a 6.6 lb bag of coal and a gallon gasoline can with a jug of water that will represent the 19.4 lbs of CO2 that is in the atmosphere from that gallon. Keeping 19 lbs of dry ice at 19 lbs on Earth Day will be quite a trick locally where temps. average about 82 F. I can however show that it will take about 20 lbs of dry wood chips to get the 5.5 lbs of charcoal we have to bury to sequester the emissions from a single gallon of gas. I can then wave a printout of the virtuous carbon cycle from the Eprida website to show them that securing the carbon can be a benefit instead of a cost.

    I’m not really sure how I could convince them to get rid of 16 lbs of fuming, hissing dry ice. It would be good to have some as a contrast though to show the difficulty of handling the stuff. It would have to stay in a “no-touching” lexan box. People get that carbon removed from the ground has to be returned to the ground as carbon.

    Terra Preta or biochar vs. “biocoal”

    David- I’m not sure where you get your information that there is somehow some advantage to burying “biocoal” as vs. biochar or Terra Preta. Terra Preta (378k results on Google) or biochar (21K hits on Google) seem to be the preferred usage for carbonized biomass used for fuel AND soil amendment whereas “biocoal” (6.5K hits Google) seems to be used in reference to the fuel usage only.

    Adding the word “abstract” to the primary in a search reinforces this impression and justifies the impression that Terra Preta (terra preta+ abstract, 12.6K hits) is the common scientific usage with biochar (biochar + abstract, 1.6K hits) gaining ground and biocoal (biocoal + abstract) having limited use largely in reference to biomass to fuel operations. A review of the scientific literature available on Google scholar also supports my hypothesis yielding 11K articles or citations for Terra Preta and 78 (as in 78) for biocoal.

    What has been repeatedly demonstrated is that adding powdered charcoal to active soil results in increased root and plant growth, thereby sequestering atmospheric carbon in addition to the carbon buried. It is therefore generally agreed that char in the active soil zone yields a carbon sequestration factor > 1. You seem to keep disputing this without references to evidence. So whether you are beating some kind of personal drum or muddying the waters could you please desist?

  8. Joe says:


    20 lbs of CO2 emitted for a gallon of gasoline (direct emissions).
    Another 4 or 5 pounds upstream (refining, etc.)

  9. David B. Benson says:

    Pangolin — No matter how many people get it wrong:

    Terra Preta is a uniquely Amazonian soil type with high carbon content.

    Biochar is a product of pyrolysis of biomass. If woody biomass is used, the traditional name is charcoal.

    Biocoal is the result of hydrothermal carbonization of biomass, a completely different (and exothermic) process from pyrolysis.

    For permanent sequestration, biocoal is perferable. Being precisely high-grade coal, we know it will stay securely buried for millions of years. Biochar will not. Read a recent report on the subject:

  10. Paul K says:

    That puts the current cost of CO2 at $200 -$250/ton.

  11. David B. Benson says:

    Paul K — Yes, biocoal at 85% carbon, if as costly to produce as coal is right now, translates into the CO2 range you mention.

  12. norman says:

    The abstract of trying to price CO2 or Carbon seems impossible given the current thinking. Maybe the pricing should consider the context of who’s producing…..who’s using? without reducing the elements ad nauseum to everyone.

  13. Karen Nyhus says:

    Thanks for making an important point, Joe.

    A sub-issue is of course the CO2 vs CO2e problem, and we get into it with atmospheric concentration calculations. Particularly since methane’s on the rise again, we may need to clarify this as well, to confirm that our total atmospheric forcing targets are sufficient – or at least whether or not we’re talking about the same target. Do you agree?

  14. I agree with Karen that there is a lot of confusion about CO2 vs CO2e targets. Apart from the different usages of CO2e, the problem becomes particularly acute when policy-makers and scientists talk about stabilizing global temperatures (where atmospheric CO2e is a more useful metric) and ocean acidity (where atmospheric CO2 is more meaningful).

    There is some discussion of avoiding confusion for climate stabilization and ocean acidification targets at

  15. Barak Gale says:

    I’m helping to organize a local project where individuals track their carbon footprint and commit to making reductions. I’m finding confusion of C versus CO2 rather ubiquitous. Please tell me – is the figure of 45,000 pounds correct for per capita CO2 footprint in US (in pound CO2, not C!)?