How Much Carbon is in the Ground?

M. King Hubbert’s Predictions
We have assumed that demand for energy will not diminish, and will simply reflect the rate of growth of the various economies of the nations. Among these, the nations that are ready and eager to grow will contribute the most new demand. One of these nations is China, which has substantial fuel resources, notably coal. With this basic assumption that people will wish to use their resources for the benefit of their economy and their standard of living, we can make a guess as to the rate of oil consumption in the future. Such a guess was made by M. King Hubbert, the oil industry's preeminent geologist, in the 1950’s. He predicted a bell-shaped curve, with U.S. oil production peaking in the 1970’s, declining thereafter. It was a good prediction. He made a further prediction that world oil production would peak in 1995-2000. Despite recent oil exploration and new finds, King's prediction is amazingly on-target. M. King Hubbert’s published estimate of the global oil production (1956) plotted on the basis of two different estimates of the amount of oil that will ultimately be produced. The colored blue line starts with the estimate of 2,100 x 109 barrels of oil as the total world oil reservoir while the black line represents an estimate of 1,350 x 109 barrels of oil.

Estimates of Fossil Fuel by Region

Different recent industry estimates of worldwide oil resource in units of GtC. (From: Odell, P. (1997) A Guide to Oil Reserves and Resources: Report to Greenpeace, p.1, Energy Advice Ltd, 1997, London. Original data are in (billion barrels) based on emission factors in the table and the conversion of 5.815 GJ/barrel of crude oil.)
Estimates of which nation has how much carbon-based resources tend to be on the low side. Oil reserves, defined as that which has been discovered and remains unused, were estimated to lie between 746 and 1056 Gb (billion barrels) at the end of 1995, with the consensus being around 1,000 Gb. In other words, 1,000 Gb of oil, or about 115 GtC of emissions (billions of barrels of oil have been converted to GtC using the factor of 0.115 GtC/Gb), can be produced at current prices with current technology (see Table).

The total amount of carbon resources available –where resources is defined as the theoretical potential based on geological information- is not known, especially if we consider the uncertainties surrounding the methane hydrate abundance. A reasonable guess (which could be off by a factor of two) is that about 8 to 10 times more carbon is available for burning than is in the atmosphere naturally. No one can say for sure what will happen as this mass of carbon is delivered to the atmosphere. If the emissions continue more or less at present rates (which seems likely given the economic “catch-up” that needs to be done by developing countries) we might predict that about one half of what is emitted stays in the atmosphere, the other half disappears into the ocean and is taken up by forest growth in the warming high latitudes. This scenario is simply an extrapolation of what happened for the last 50 years or so, a procedure that has many pitfalls, but probably no more pitfalls than running existing computer models forward in time.

With this scenario, we can expect a doubling of the greenhouse effect by 2050, an event that would seem to be difficult to avoid. At that point, the various responses of the climate system will be much clearer than now. For example, will the ocean continue to take up the same portion of carbon dioxide as it did in the past? Will gases other than carbon dioxide become ever more important, so that the uptake by the ocean (which concerns carbon dioxide but not methane or nitrous oxide) will become successively less important? Will the warming produce more methane? Will the warming of the upper ocean deny oxygen to shallow waters thus enhancing nitrate reduction, with additional nitrous oxide going off to the atmosphere?

Future Regulation of Fossil Fuel Emissions
With this information in hand, the world's nations might decide to make another Montreal-type agreement, this time concerning the emission of carbon dioxide, methane and nitrous oxide. Or, if no unacceptable damage has been detected, the world's nations may decide to "stabilize emissions" or even to decrease them slightly, being by now totally dependent on carbon-based energy for their economies. Of course, at some point, "stabilizing emissions" may simply describe the intent of the participating nations, but not what is happening within the system. If the system responds to warming by emitting its own mix of greenhouse gases (carbon dioxide from growth blooms of certain micro-algae, methane from melting methane hydrates, nitrous oxide from reducing nitrate) it may not be possible to stabilize emissions by actions agreed on, and the natural system will take over the initiative. On the other hand, the natural system may be quite resilient to disturbance, so that nothing much will happen when doubling the greenhouse effect.

With 10 times more carbon available than is already in the atmosphere, however, a five-fold increase of atmospheric trace gases is not out of the question, within the next few centuries. Such a situation cannot be computed at the present time, since the various "physical constants" used in describing climate dynamics are likely to be out of range. Also, there are no analogs anywhere in "recent" geologic experience. We probably have to go back to the time of the dinosaurs to an ice-free planet to find a situation comparable to the one we are capable of generating when burning all that is in the ground.

It is perhaps well to remember that the present Earth system is in a general cold phase with ice in polar regions (i.e. Antarctica and Greenland). This has (at least) two consequences. One is that the system, in order to achieve equilibrium with its new atmosphere, will make serious adjustments that will be experienced as rapid change in ocean circulation, wind field, and ocean chemistry. Another is that plants and animals will not have experienced any such changes before and will therefore not be adapted to cope with them.