A Big Source of Climate Confusion: The Factor of 3.67 Difference Between Carbon vs. Carbon Dioxide

One of the biggest source of confusion and errors in climate discussions concerns “carbon” versus “carbon dioxide.”

I was reminded of this last week because of my post Economics Stunner: “Oil and Coal-Fired Power Plants Have Air Pollution Damages Larger Than Their Value Added.” I noticed that Skeptical Science innocently confused C and CO2.

The economists had written, “We assume that the central estimate of the social cost of carbon is $27 per ton of carbon” (which is to say a measly $7.36 per ton of CO2).  SkS assumed the authors meant CO2 couldn’t believe that leading economists could possibly have lowballed climate impacts so much.  As SkS writes in their correction, this puts their social cost of carbon “near the lower limit we have seen in recent economic studies!”

SkS needn’t feel bad.  I’ve seen this mistake made a dozen times — in fact, I got an email from the Director for Modeling and Analysis at one of the largest  fossil fuel companies in the world about my post, and he got it backwards!

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.

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).  Still, they use the terms interchangeably, as I and almost everyone else who writes in this space does, which only adds to the confusion.  You’ll read things like “The price of carbon is $10 a ton of CO2.”

But the central climate number in this whole arena 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.

In my books, I have tried to consistently use CO2, for clarity’s sake, but haven’t been quite as consistent in the blog.  So I am going to try to more consistently use CO2. Where relevant I will also include one conversion to carbon, too, without bombarding you with too many numbers.

And whenever I write a post where tons or cost per ton matters, I’ll link to this post.  If nothing else, it’ll remind me to check my 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.  Don’t assume the authors of the original piece got their math right.

Oh, and people often switch metric tons (tonnes) and short tons.  Here’s that conversion:


21 Responses to A Big Source of Climate Confusion: The Factor of 3.67 Difference Between Carbon vs. Carbon Dioxide

  1. Mike Roddy says:

    I agree that CO2 should become the standard, especially since that’s what oft cited EIA uses. We also need to change the phrase “pricing carbon” to “pricing CO2 emissions”, especially since carbon appears in nature in so many forms.

  2. prokaryotes says:

    Carbon is released into the atmosphere in several ways:

    Through the respiration performed by plants and animals. This is an exothermic reaction and it involves the breaking down of glucose (or other organic molecules) into carbon dioxide and water.
    Through the decay of animal and plant matter. Fungi and bacteria break down the carbon compounds in dead animals and plants and convert the carbon to carbon dioxide if oxygen is present, or methane if not.
    Through combustion of organic material which oxidizes the carbon it contains, producing carbon dioxide (and other things, like water vapor). Burning fossil fuels such as coal, petroleum products, and natural gas releases carbon that has been stored in the geosphere for millions of years. Burning agrofuels also releases carbon dioxide which has been stored for only a few years or less.
    Production of cement. Carbon dioxide is released when limestone (calcium carbonate) is heated to produce lime (calcium oxide), a component of cement.
    At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is released back into the atmosphere.
    Volcanic eruptions and metamorphism release gases into the atmosphere. Volcanic gases are primarily water vapor, carbon dioxide and sulfur dioxide. The carbon dioxide released is roughly equal to the amount removed by silicate weathering;[citation needed] so the two processes, which are the chemical reverse of each other, sum to roughly zero, and do not affect the level of atmospheric carbon dioxide on time scales of less than about 100,000 years.

  3. Joan Savage says:

    Thanks a ton, Joe!
    (actually billions of tons..)

    As you know, but didn’t mention, this clarification may also help define the policy talk about atmospheric methane, a part of the carbon cycle which should not be merely added to CO2.

    Focus on carbon dioxide reduction policy, yes!

  4. catman306 says:

    Thanks Joe, this carbon – carbon dioxide confusion has been bothering me for quite some time.

    Carbon is no threat. Carbon dioxide can kill (by suffocation) in moderate concentrations or is a powerful greenhouse gas.

  5. Tom Fiddaman says:

    The other nasty surprise in typical statements about central estimates of the social cost of carbon is that analysts conflate uncertainty about the physics/economics of the situation (climate sensitivity, scale of impacts) with ethical choices (discounting and equity weighting). As a rule, the lowball SCC estimates involve significant discounting for pure time preference (grandkids don’t matter), which pioneering economist Frank Ramsey described in 1928 as “a practice which is ethically indefensible and arises merely from the weakness of the imagination.”

    This is evident, for example, in Tol’s survey.

  6. Dr.A.Jagadeeesh says:

    You always write with authority Joe Romm and this discussion on Carbon Vs Carbon Dioxide is no exception. Congratulations.

    Dr.A.Jagadeesh Nellore(AP),India

  7. Dan says:

    Something I’ve found more confusing than the tC vs. tCO2 distinction is the ppm CO2 vs. ppm CO2-eq distinction. Is there a chance you could do a post on that, Joe?

  8. Raul M. says:

    As an observer, I was confused about that tip point talk.
    I’m glad that so many have worked to clarify that the tip
    actually happened back at 350 ppm of co2. Living things start to fall slowly at first and as gravity gains the free force, the fall becomes faster. That mankind will put the chute out to slow the fall has yet to be seen, as
    ppm continues to climb. Some have guessed right and know mankind is falling even faster than before.
    Joe and others have done well in saying just how large a chute will be needed to turn the climate back to under 350 ppm. Meanwhile some notice when they step out in the morning it not like what they had planned for all those years. I’m glad that this year we didn’t get that monster of a storm that could cover most of Florida.
    Word is that 2012 could be a La Nina year also so we might not see the monster up close for another year as well.

  9. dana1981 says:

    The main reason I made the mistake in my Skeptical Science article is that the Nordhaus study would have made a lot more sense had their numbers been in tons of CO2 as opposed to tons of carbon. Careless on my part to assume that their study assumptions would make sense though!

  10. MA Rodger says:

    I’ve never hear a ‘short’ ton called an ‘english’ ton before. The alternative name I hear is ‘tons US’.
    Here in merry England some of us still use the old Imperial tons (I believe also called ‘long’ tons) which weigh 2,240lbs so close enough to the weight of a metric tonne to ignore the difference.

  11. P Baker says:

    Yes you are right, the short US ton is 2000 lb and the UK long ton is 2240 lb.

  12. Joan Savage says:

    Replying to both Mike Roddy #1 and prokaryotes #2-

    To fine tune without getting lost, ‘Reduce fossil-sourced carbon dioxide emissions,’ is high priority.

    It’s still about the fossils.

    CO2 emissions from fossil fuel are linked to the other excess atmospheric carbon emissions. Cement manufacture doesn’t go large without fuel for mixing and delivery. I think of another, animal methane release. It wouldn’t be as big a deal if it were not for related food processing and food delivery that enables the mass meat production. All that rides on the fossils.

    So I hope I’m with the program, tons of CO2 emissions is the chief metric, and fossil sources are the pivot points.

  13. Brian says:

    To extend the discussion further to consider carbon as a percentage of fossil fuels and also of biomass opens upo the idea of much easier CCS alternatives.

    Fossil fuels are substantially C(n)H(2n+2). For example methane n=1 and gasoline n is mostly 7 but either way C remains about 85% of the mass of both fossil fuels.
    Biomass its substantially CHO (ignoring nutrients) IIR where the Oxygen atom dominates weight.
    So on a carbon atom for carbon atom basis, very dry bio mass has roughly twice the weight of fossil fuel.

    I have often wondered why we even contemplate CCS from the atmosphere when it would be much easier to sequester the C before it has a chance to become CO2. The C in CO2 is fungible after all.
    Leaving fossil fuels in the ground deprives us of their energy so thats a difficult sell.
    But for every ton of fossil fuel for which we need to sequester 3.67 tons of atmospheric CO2 we could instead sequester 2 tons of dry biomass from decomposing somewhere where it is not enriching any soil.

    The carbon cycle is some 300GT of CO2 IIR which is about 10x that of our global CO2 release. There is probably a few GT of human accessible biomass around the globe that could be benignly diverted from the carbon cycle.
    To keep the embodied energy of collecting, hauling and burying this biomass, it has to be done very locally around available fill sites and replicated around the globe. A side benefit is that methane will be produced in high concentrations (compared to landfills) so selling this provides a carbon neutral fuel to boot.
    Each 2 T of buried biomass has to cost a lot less energy than doing CCS of 3.67 T from the atmosphere, liquifying it then piping it long distances to relatively few but vast geologic undreground sites.

    Ofcourse making biochar and providing municipally supported compost from such collected waste biomass would be beneficial too but burying it accelerates what nature does over millenia anyway.


  14. Mark Shapiro says:

    The press (and my friends) also confuse power with energy.

    Power = energy / time (energy per unit of time).
    Energy = power * time.

    Watts, KW, MW, GW, and TW are power.
    Watt-hours, KWh, MWh, GWh, and TWh are energy.

    BTUs per hour is power.
    BTUs are energy.

    (Did I get it right?)

  15. dick smith says:

    Joe, a ton is a ton. (Remember the kid’s joke, “which is heavier, a ton of feathers or a ton of bricks?”)

    I’d caution that an equation format is probably not the best way to avoid confusion.

    Having tried to explain this without saying 1 ton = 3.67 tons, I’ve decided its more accurate to say, “a molecule of CO2 weighs 3.67 times more than a molecule of carbon.”

  16. dick smith says:

    There are some other implications.

    This becomes particularly important in considering revenue estimates from fee-and-dividend proposals. The revenues collected from a tax on tons of co2 “emissions” will be 3.67 times higher than a tax on tons of “carbon.”

    Fee and dividend proposals usually collect the tax at the first point of sale of CARBON, but the revenue assumptions are based upon the CO2 EMISSIONS potential. So, statutory language that reads, “$10 per ton tax on CO2 emissions” is really a $36.70 per ton tax on carbon at that first point of sale.

    Rep. Paul Stark is drafting a bill. A written summary carelessly stated that a $10 per ton fee on carbon would raise about $50 billion a year. No it won’t. In the U.S. we emit somewhere north of 5.5 billion tons of CO2. A $10 per ton tax on 5.8 billion tons will raise “about $50 billion” a year. But, we only use between 1.5 and 1.6 billion tons a year of carbon. A $10 per ton tax on carbon would only yield between $15-16 billion annually.

    Finally, saying, “we need to put a price on carbon,” is punchy. But, when you draft the legislation to collect the tax on carbon at the first point of sale, if you want to put that lowball $10 per ton figure in the bill (understandably, that sounds better than $36.70 per ton) make sure your bill draft (and your bill summary) is more carefully worded than the one I saw.

  17. Tim says:

    Ummm… if you’re going to show a “picture” of CO₂, let’s do it right. The molecule is linear, not bent.

  18. Tim says:

    It is too bad we use these silly kW-h units though. A kW-s is a kJ – it would be much easier if we just used kilojoules (or megajoules)!

    1.0 kWh = 1.0 kW × 3600 s = 1.0 kJ/s × 3600 s = 3600 kJ = 3.6 MJ

  19. Joe Romm says:

    That will only confuse 99% of people.

  20. Dan @ 7 – you might find the explanation of CO2-eq at helpful

  21. Joe, it may also be useful to state a CO2 vs CO2-eq policy clearly. You seem to normally use CO2-only figures for stabilisation targets so your blob policy might state:

    “On this blog we use atmospheric carbon dioxide concentrations to discuss policy targets for anthropogenic climate change and ocean acidification (e.g. 350ppm, 450ppm, 550ppm CO2). The use of carbon dioxide alone should not be confused with stabilization targets based on ‘carbon dioxide equivalents’, which includes the effects of all long-lived greenhouse gases and, in some contexts, the effects of other radiative forcing agents such as aerosols and landuse changes (IPCC 2007).”