A commenter here a while back argued that RCP 8.5, the highest emission scenario in the current IPCC report, is impossible, because it requires more coal than is available to be mined. I recently came across a more detailed version of that argument in a published piece by David Rutledge, a Caltech professor.
The argument is straightforward. Estimates of coal reserves are much more reliable than estimates of reserves of oil and gas, coal being a solid. Such estimates have been made for more than a century and actual quantities mined have, so far, been consistent with them. In particular:
for coal the pattern has been that countries produce only a small fraction of their early reserves, and then late in the production cycle the reserves drop to match the coal at the last working mines. This pattern is seen in the UK (cumulative production of 19% of early reserves), Pennsylvania anthracite (42%), the Ruhr Valley (14%), France and Belgium (23%), and Japan and South Korea (21%). This means that the reserves criteria have been too optimistic, but it also means that world coal reserves are a good upper bound on future production.
By the author's calculation, RCP 8.5 requires the world to consume 200% of total coal reserves by 2100, 700% by 2500. If he is correct, it follows that RCP 8.5 ought not to be included in the IPCC graphs showing possible future climate change and that maximum values of temperature change or sea level rise ought not to include the values it would imply.
I have two questions for readers:
1. Can anyone point at a serious mistake in the argument? Does it misstate the amount of coal consumption implied by RCP 8.5, the size of coal reserves as currently estimated or the reasons to think that current estimates represent a reasonable upper bound?
2. Is there anyone here otherwise inclined to support the IPCC who, having looked at this argument, agrees that the inclusion of RCP 8.5 in the report is fraudulent, an attempt to make risks of future warming look worse than they actually are?