Nature Climate Change | Climate Feedback

AGU 2008: Peak fuel reserves

Whether peak oil is good news for the climate ultimately depends on what replaces oil as our staple fuel source. It will be unsurprising to most that replacing dwindling oil reserves with coal would do little to solve the climate problem, but how much coal remains is also highly uncertain, according to Prof. David Rutledge of Caltech, who spoke to the press at the AGU this morning.

Andy Dessler of Texas A&M touched on this in a guest commentary posted here last month. In short, Dessler called for a global IPCC-like assessment of our fossil fuel reserves, pointing to a new analysis by Rutledge that shows the world’s available coal reserves are far lower than traditional estimates would suggest. If Rutledge’s estimates are correct, combustion of all remaining conventional oil, gas, and coal reserves would produce an atmospheric concentration of carbon dioxide of approximately 470 ppmv in 2100, near the stabilization target that many climatologists argue we must achieve to avoid the worst impacts of climate change.

While Rutledge’s estimates suggest that the worst-case scenarios of the IPCC may be unachievable, Ken Caldeira of Washington’s Carnegie Institute had a more sobering message. Caldeira and colleagues used a climate and carbon cycle model to look at how running out of oil could affect future climate scenarios. Their analysis showed that if we replaced oil with liquefied coal fuel promptly, we would reach 2°C above pre-industrial temperatures in 2042 instead of 2045. Replacing oil with renewables, however, would delay reaching 2°C above pre-industrial temperatures by 11 years. This is simply because per coal emits more carbon dioxide per unit of energy than oil; add to that the energy costs associated with conversion of coal to liquid fuels, a likely option if we run out of oil.

Even if Rutledge is correct in his estimates of available reserves, we’d still easily have enough to overshoot the 2°C target it seems, and we’ll need Herculean efforts to avoid it, a point that has been repeated numerous times over the past few days. Kharecha, who has been working on this issue with James Hansen, called for a zeroing of carbon emissions from coal by 2030 and stabilization of atmospheric concentrations at 350 ppmv.

But Rutledge’s estimates have important implications for the amount of change we can expect in the longer term. I asked him about the feasibility of reassessing global fossil fuel reserves and he highlighted the political improbability of it, but he suggests the IPCC include an additional scenario in their next assessment to account for lthe real possibility of lower available coal reserves.

Olive Heffernan


  1. Report this comment

    David Lewis said:

    Stephen Chu has been saying that coal is “so plentiful there’s no serious exploration for it”. Chu co-chaired a study panel for the InterAcademy Council that produced “Lighting the Way”.

    It will be interesting to see if people have been this wrong about coal.

    Rutledge is a Professor of Electrical Engineering, in case that makes a difference to anyone who thinks he might be a geologist.

    He takes the widely perceived observation voiced by Chu and states that when the subject has been more thoroughly examined, we will find out there isn’t even enough coal to bring on the climate cataclysm we’ve all been looking forward to studying.

    Quote from Mark Twain, found on Rutledge’s video presentation:

    “There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact”

    If there really is doubt about how much coal there is there should be a serious look at the size of the reserves, duh, obviously.

  2. Report this comment

    ccpo said:

    Unfortunately, what Dr. Rutledge dies not say in his paper is that it is grossly simplified, to the point of being nearly useless with regard to issues of Climate Change. I do not quarrel with Rutledge’s coal deposit numbers, though they have not been confirmed by an other researcher that I am aware of.

    I quarrel with his choice to ignore known feedbacks, to run MAGICC using only one scenario, e.g., he used only one sensitivity, not a range – this despite Hansen, et al. warning of possibly much higher climate sensitivity. Since he completely ignored other feedbacks, using a range of sensitivities to balance that should have been standard procedure.

    Further, Rutledge considers only CO2 and only CO2 from fossil fuels. This is bizarre given the research done prior to his presentation at the AGU of methane and CO2 emissions from permafrost and sea bed methane (clathrates) and the resurgence of the rise in atmospheric methane.

    Even more astounding, Rutledge presented his work on The Oil drum and had the various weaknesses of his paper pointed out. In subsequent discussions there, he refused to run the software at higher sensitivities citing time constraints. (I have used MAGICC and know it is possible to change these settings in seconds and run the model in minutes, so I wonder at this explanation.)

    Another problem is that the vast majority of climate scientists responding to recent polls have supported the idea that 450 is too high and we are very unlikely to keep temps at 2C.

    Lastly, Rutledge ignores completely that, as you point out, 450 is quite likely far too high for CO2, thus making his paper not on;y flawed, but irrelevant.

    That Rutledge has no training in climate science is obvious by the overly simplified approach he takes in extrapolating his assumptions on coal reserves out to effects on climate. This is a dangerous thing to do: produce a paper as a scientist and all the weight that implies, but in an area that you have zero background in. His paper is being used by those who would minimize the importance or seriousness of climate change – even its existence – to say we can burn all the fossil fuels we wish.

    Had Rutledge stopped at estimating fossil fuel reserves then asked the question of the implications on climate of his climate researcher peers, I would have no beef with the paper.

    It does not help that this paper, so far as I know, has not been published in a peer-reviewed journal.

    Rutledge needs to either 1. respond to the critiques by updating his paper to include a range of sensitivities and fast and slow feedbacks, or 2. have it pass through the rigors of peer review.