Yesterday, I posted that the total budget of fossil fuel emissions we can ever emit is 1 trillion tonnes of Carbon. And that we’ve burnt through about half of that since the dawn of industrialization. Today, I read in the Guardian that existing oil reserves may have been deliberately overestimated by the International Energy Agency. George Monbiot explains how frightening this could be, given the likely impact of lower oil supplies on food production. Madeleine Bunting equates the reluctance to discuss this with the head-in-the-sand attitude that preceded last year’s financial crisis. Looks like the more pessimistic of the peak oil folks may have had it right all along.

None of these articles however makes the link to climate change (Monbiot only mentions it in passing in response to comments). So, which problem is bigger, peak oil or climate change? Does one cancel out the other? Should I stop worrying about the trillionth tonne, if the oil simply doesn’t exist to get there?

A back of the envelope calculation tells me that more than half of the world’s estimated remaining reserves of fossil fuels have to stay buried in the ground if we are to stay within a trillion tonnes. Here’s the numbers:

  • Oil: The Energy Watch Group estimates there are 854 Gb (gigabarrels) of oil left, while industry official figures put it at well over 1200Gb). Let’s split the difference and say 1,000Gb (1×10^12). Jim Bliss calculates that each barrel of crude oil releases about 100kg of carbon. That gives us 0.1 trillion tonnes of Carbon from oil.
  • Coal: Wikipedia tells us there are just under 1 trillion tonnes of proved recoverable coal reserves, and that coal has a carbon intensity of about 0.8, so that gives us 0.8 trillion tonnes of Carbon from coal.
  • Natural Gas: The US EIA gives the world’s natural gas reserves as about somewhat over 6,000 trillion cubic feet, which converts to about 170 trillion cubic meters. Each cubic meter gives about 0.5kg Carbon, so we have 85 trillion kg, or 0.08 trillion tonnes of Carbon from gas.

That all adds up to about 1 trillion tonnes of carbon from estimated fossil fuel reserves, the vast majority of which is coal. If we want a 50:50 chance of staying below 2ºC temperature rise, we can only burn half this much over the next few centuries. If we want better odds, say a 1-in-4 chance of exceeding 2ºC, we can only burn a quarter of it.

Conclusion: More than one half of all remaining fossil fuel reserves must remain unused. So peak oil and peak coal won’t save us. I would even go so far as to say that the peak oil folks are only about half as worried as they should be!


  1. Jim Bliss calculates that each barrel of crude oil releases about 100kg of carbon. That gives us 0.1 trillion tonnes of Carbon from oil.

    Actually, no I didn’t. I calculated that every barrel of crude oil releases about 317kg of carbon dioxide. That throws your oil numbers out by a factor of three.

    Regarding the general issue though, it seems to me that unless we adopt a radically different set of values; a new cultural ethos if you will; then peak oil is almost guaranteed to exacerbate Climate Change rather than act as any kind of safety valve.

    Oil is a tremendously useful source of energy and any reduction in the amount of oil available almost always requires a larger increase in other energy sources to compensate than might initially be imagined. If you want to power an automobile with coal for instance, it requires conversion into something convenient for a car… electricity, hydrogen, etc. But this conversion process is generally less energy efficient than oil refining, so the total amount of energy consumed by the system must increase merely to maintain the same level of net energy available to end users.

    And something that is rarely factored into Climate Models is the concern (a very real concern in my view) that as fossil energy resources get depleted, so wood may once again become economically viable as an energy source. This could significantly increase deforestation rates if we’re not careful.

    In my view we need a complete revolution in the way we think about and organise human life on this planet. And I suspect I’d get very long odds indeed if the bookmakers were taking bets on that happening.

  2. Jim: Thanks for the quick response. But I’m not calculating mass of CO2, I’m calculating mass of C. It’s a 3.66 conversion factor, which I decided was close enough to your 3.17 that I could just assume that virtually all of your 100.73kg of liquid fuel was carbon. I should probably have had it at about 90kg of carbon to be more accurate.

    The comments about energy efficiency of oil as a transportation fuel are interesting. But Jacobon & Delucchi make the opposite point in their recent Scientific American article: only 17% – 20% of the energy in gasoline goes to move a vehicle, the rest is wasted as heat. Whereas in an electric car is 75% to 86% efficient (dunno where they get the numbers from – I will explore). So, their argument is that a vehicle fleet powered from renewables (they favour wind and solar) would actually require significantly less energy. I’d love to map out their numbers and yours to compare them…

    But I won’t dispute the rest of your comments – we do indeed have very long odds.

  3. Actually, Jeremy Leggett in “Half Gone” explains that just burning the remaining oil would push us through into dangerous climate change, let alone the gas. The coal could, from this vantage point of having burnt the foul stuff for the last 200 years, still cook the planet 5 times over. I don’t know how he’s run his numbers but they are his figures.

    So unless peak oil pushes us into all out nuclear-war over the remaining oil, I don’t think it is going to solve climate change for us. And IF “Judgement Day” happens, then we’ll have more to worry about than climate change. (Nuclear winter?)

    Not many nice scenarios out there for our future, so I read now and then just to make sure I don’t lose it totally.

  4. This is an interesting question. It makes me think that the strategy of focusing on coal (which has the highest total in trillions of tons in your calcuations by far) as the greatest threat to climate is valid.

    There some systems considerations here however that just don’t allow for easy back of the envelope calculations, IMHO. All of our heavy machinery used to mine and access the natural gas and coal RUNS on oil. This is billions and billions of dollars of machinery. Practically all of our transportation system runs on oil. This means that if we reach peak oil much earlier than anticipated that the shortages of oil could create big difficulties in accessing the coal that might be very difficult to recover from.

    What I am trying to say is that in an energy descent scenario, I don’t think you can just calculate reserves and assume we would be able to get them out of the ground economically.

    I still do think coal is the biggest strategic focus for climate activists… it is the dirtiest fuel and most abundant. Oil is starting to deplete itself… if we can keep the oil companies out of CTL, TarSands and Oil Shale… that’s the key.

  5. Steve,

    There is an issue with your assessment: you treat reserves as fixed. (Un)fortunately, none of those figures are actually fixed, and are likely to continue growing at least in the near future. Depending on your point of view, that is good or bad, but I think it’s a serious thing to consider when you discuss recovery of a resource from that post’s perspective.

    In discussions of commodities, you always have to distinguish between reserves (which represent the current, economically recoverable resources) and ultimate recoverable resource (URR) (which represent the estimated “in the ground” resource). In other words, reserves can fluctuate, and in fact grow based on current technologies. For example, tertiary recovery of oil or the economizing of shale gas recently. This is an important issue that makes both projections of production as well as CO2 emissions based on use of the fuel so difficult.

  6. There is some pretty good peer reviewed literature on this subject from James Hansen himself. His basic conclusion, if I recall it correctly, was: burn all the conventional oil and natural gas you want, but get off coal immediately.‘peak-oil’-for-atmospheric-co2-and-climate/

    Kjell Aleklett, head of the Association for the Study of Peak Oil and a bonafide academic (albeit in a different area) has basically the same take on it even though he believes there is less coal and oil in the ground than Hansen et al. assumed: he’s said that Russia and the U.S. need to not burn half their remaining coal reserves.

    So if you take Hansen as one end of the spectrum and Aleklett as the other, you’ll find that no one who is serious about this subject disagrees with the notion that there is enough fossil fuels in the ground to complete screw us.

  7. Yeah, I saw the Hansen paper when I was researching this post. I was hoping to find out from his paper whether I’d got the numbers approximately right, or made some basic mistake. Unfortunately, he doesn’t anywhere tackle the simple question of what proportion of the remaining reserves should we (not) burn. Instead he goes for a much more sophisticated analysis of energy choices. Which is great, but not much help for my original question. I didn’t find the Aleklett analysis though. Do you have a reference for it?

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