Keystone XL: Game over?

  • The peak warming is linearly proportional to the cumulative carbon emitted
  • It doesn’t matter much how rapidly the carbon is emitted
  • The warming you get when you stop emitting carbon is what you are stuck with for the next thousand years
  • The climate recovers only slightly over the next ten thousand years
  • At the mid-range of IPCC climate sensitivity, a trillion tonnes cumulative carbon gives you about 2C global mean warming above the pre-industrial temperature.

This graph gives you an idea of what the Anthropocene climate looks like as a function of how much carbon we emit before giving up the fossil fuel habit, without even taking into account the possibility of carbon cycle feedbacks leading to a release of stored terrestrial carbon The graph is from the NRC report, and is based on simulations with the U. of Victoria climate/carbon model tuned to yield the mid-range IPCC climate sensitivity. Assuming a 50-50 chance that climate sensitivity is at or below this value, we thus have a 50-50 chance of holding warming below 2C if cumulative emissions are held to a trillion tonnes. Including deforestation, we have already emitted about half that, so our whole future allowance is another 500 gigatonnes.

Proved reserves of conventional oil add up to 139 gigatonnes C (based on data here and the conversion factor in Table 6 here, assuming an average crude oil density of 850 kg per cubic meter). To be specific, that’s 1200 billion barrels times .16 cubic meters per barrel times .85 metric tonnes per cubic meter crude times .85 tonnes carbon per tonne crude. (Some other estimates, e.g. Nehring (2009), put the amount of ultimately recoverable oil in known reserves about 50% higher). To the carbon in conventional petroleum reserves you can add about 100 gigatonnes C from proved natural gas reserves, based on the same sources as I used for oil. If one assumes that these two reserves are so valuable and easily accessible that it’s inevitable they will get burned, that leaves only 261 gigatonnes from all other fossil fuel sources. How does that limit stack up against what’s in the Athabasca oil sands deposit?

The geological literature generally puts the amount of bitumen in-place at 1.7 trillion barrels (e.g. see the numbers and references quoted here). That oil in-place is heavy oil, with a density close to a metric tonne per cubic meter, so the associated carbon adds up to about 230 gigatonnes — essentially enough to close the “game over” gap. But oil-in-place is not the same as economically recoverable oil. That’s a moving target, as oil prices, production prices and technology evolve. At present, it is generally figured that only 10% of the oil-in-place is economically recoverable. However, continued development of in-situ production methods could bump up economically recoverable reserves considerably. For example this working paper (pdf) from the National Petroleum Council estimates that Steam Assisted Gravity Drainage could recover up to 70% of oil-in-place at a cost of below $20 per barrel *.

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