All resources are finite, and we tend to go for the easily extractable stuff first. Therefore, as we start to exhaust our reserves, production will tend to taper off, with the law of diminishing returns demanding ever more physical, economic and technological effort to access what’s left. In this sense, the concept of the ‘peak’, most commonly used in discussions of ‘peak oil’, is a conceptual no-brainer. Where things become controversial is that the methods used to calculate the timing of the peak, the remaining extractable reserves, and the post-peak production trajectory, often rely solely on extrapolating from the history of past production, taking few cues from geological knowledge, uncertainties about future economics, and the prospect of future technological advances. Or, more accurately, the ‘peakist’ argument seems to be that these factors have little long-term effect, and that the mismatch with generally more optimistic geologically based reserve estimates is a feature, not a bug.
It’s unsurprising that most analyses of this sort have focussed on oil, but you can theoretically do the same for any other resource, including, as has just been reported in Science, coal. David Rutledge of Caltech is one of those who has crunched the numbers, and just as with oil, has found that this method points to there being rather less remaining than more conventional reserve estimates would have you believe:

Applied to 14 major coal-producing regions, Rutledge’s method gives a world ultimate production of 660 billion metric tons. That’s only one-quarter of geologic estimates of ultimate production, he says.

As to when coal will peak, Rutledge declines to say, citing the way peak timing varied widely among regions already well past their peak. He will say, however, that in his projection the world will have produced a whopping 90% of its coal by 2069. Physicist Mikael H????k of Uppsala University in Sweden and his colleagues are willing to point to a peak. They have taken a similar approach to Rutledge’s but with some reliance on estimated reserves. Still, they see world coal production topping out by 2020, entering a 30-year-long plateau, and then declining.

If true, or even close to true, these conclusions have some rather thought-provoking ramifications. The standard estimates give us somewhere in the region of 150-200 years’ worth of coal left in the ground. On the one hand, this gives our fossil fuel-addicted economies a fall-back as oil and gas reserves are depleted; on the other hand, the impact of actually using all that coal on atmospheric CO2 levels, and hence our climate, are rather scary (the as-yet-unproven potential of carbon capture notwithstanding). If we do start running out of coal sooner rather than later, then raw economics – a force seemingly much more powerful than either our consciences or our sense of self-preservation – might force us down a less environmentally damaging path, but our room for manoeuvre in weening our economies off carbon is more severely restricted than we had previously imagined.