by Dave Rutledge

Now that Working Group 3 has put its chapters on line, all six thousand pages of the IPCC’s 5th Assessment Report have arrived. Coal is the specter that looms.

In the IPCC’s business-as-usual scenario, Representative Concentration Pathway (RCP) 8.5, coal accounts for half of future carbon-dioxide emissions through 2100, and two-thirds of the emissions through 2500. The IPCC’s coal burn is enormous, twice the world reserves by 2100, and seven times reserves by 2500. Coal so dominates that it is not an exaggeration to say that the IPCC and climate-change research programs depend on this massive coal burn for their existence. Without the threat of coal, the IPCC could close up shop and the research program funding would drop to a small fraction of what is spent on research in weather forecasting.

Coal is the oldest of our fossil fuels, and we know a lot about how coal mining grows and how it dies. We also know a lot about coal reserves. The UK produced the first detailed reserves study in a Royal Commission on Coal Supplies in 1871. Dever Ashmead of the US Bureau of Mines compiled a thorough reserves analysis of the Pennsylvania anthracite fields in 1926. The first comprehensive survey at the world level was The Coal Resources of the World, produced in 1913 for the 12th World Geological Congress. After the First World War, the surveys were continued by the World Power Conference. This group, now called the World Energy Council, published its latest survey, the 23rd, in 2013. The Council’s surveys are the primary source for coal reserves.

One thing that distinguishes coal reserves from oil and gas reserves is that historically they have had the goal of serving as an estimate of total national future production. This is explicit in the 1871 Royal Commission charter, and the Commission’s reserves criteria were adopted in the later World Power Council surveys. This is reasonable because coal fields are relatively easy to find and map. This is in contrast to oil and gas, where discovery has been difficult. This can make oil and gas reserves behave like warehouse inventories that are an index of the time that it takes to develop new fields rather than total future production. US oil reserves have been typically been close to the production in the following ten years.

On the other hand, 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. An IPCC scenario that burns two times or seven times the reserves is utterly at odds with the historical experience.

Peer-reviewed estimates of future world coal production have been available. One example is my 2011 paper in the Journal of Coal Geology, “Estimating Long-Term World Coal Production with Logit and Probit Transforms“. This paper includes references to other peer-reviewed studies led by Tad Patzek, Chair of the Petroleum and Geosystems Engineering Department at the University of Texas at Austin, and Steve Mohr, at the Sydney University of Technology. All three papers use production histories to make an independent estimate of future production that is less than reserves, but consistent with the historical experience of mining coal.

I searched the 5th Assessment Report for references to coal reserves and I found one quantitative sentence in Working Group 3, Chapter 7, page 15.

“For both reserves and resources, the quantity of hard (black) coal significantly outnumbers the quantity of lignite (brown coal), and despite resources being far greater than reserves, the possibility for resources to cross over to reserves is expected to be limited since coal reserves are likely to last around 100 years at current rates of production (Rogner et al., 2012).” [The Rogner et al. reference is to a chapter in the book Global Energy Assessment by the think-tank IIASA.]

It is true that the R/P (reserves to production) ratio is 109 years. However, the R/P ratio has been dropping rapidly. Ten years ago it was 204 years. It is also true that conversion of resources to reserves is expected to be limited, but for a different reason. Countries end up producing less than their reserves. Most importantly, the statement does not address the problem, which is the large multiple of the coal reserves that is assumed to be produced in the business-as-usual scenario, RCP8.5. There is no precedent for this, and RCP8.5 should not be used for any purpose whatsoever.

Notes

The IPCC is actually rather coy about revealing exactly how much coal is burned in RCP8.5. If one goes to the RCP data base, one can find the emissions in 2500 for the insulation chemical HFC245fa, which has a current production of 500t. However, there is nothing for coal, which has a current production of 8Gt. The 2011 paper in Climatic Change by Keywan Riahi et al. that defines the RCP8.5, “RCP 8.5—A scenario of comparatively high greenhouse gas emissions.”, gives a graph (Figure 5), presumably indicative, that shows coal production increasing to 2100, but with no discussion of the fact that it exceeds reserves. For the numbers given here, I digitized this figure and extended the calculation to 2500.

Some thoughts on more realistic projections for future fossil-fuel production were given in an earlier Climate Etc. post, and in a recent invited talk for the Geological Society of America, “Projections for Ultimate Coal Production from Production Histories Through 2012,” I argue that future fossil-fuel CO2 emissions without any climate policy at all are likely to fall between those of the policy scenarios RCP2.6 and RCP4.5.

Biography for David Rutledge

Professor Rutledge is the Tomiyasu Professor of Engineering at Caltech, and a former Chair of the Division of Engineering and Applied Science there. He is a Fellow of the IEEE and a winner of the Teaching Award of the Associated Students at Caltech. He served as the editor for the Transactions on Microwave Theory and Techniques, and is a founder of the Wavestream Corporation, a manufacturer of high-power millimeter-wave transmitters for satellite uplinks.

JC note: David Rutledge has posted previously at CE Energy supplies and climate policy . Since this is a guest post, please keep your comments relevant and civil.