There is more energy available in coal reserves than in oil or natural gas. Coal reserves are also more widely distributed between countries of the world than other fossil fuels. Getting a handle on how much coal is left for the world to use is not simple. The most widely agreed upon number is around 900 billion tons, from the U.S. Energy Information Administration, the World Energy Council, and BP's annual report on energy assets. This number is the amount of "Proven" reserves, which is not the total amount of coal in the ground, but the amount that makes economic sense to dig up under current conditions.
|Where is the Coal? (Gunnmap)|
None of that answered the question of how long the questionable amount of coal reserves will last. If we assume those 900 Billion tons are all we can mine, then it will last about 120 years at current production. But worldwide coal production and usage has been climbing rapidly, at a little over 5% per year for about the last ten. If that continues, then the world will run out in 40 years.
That scenario is unlikely, even without a push towards renewable electricity. The growth will start to plateau at some point. But some growth will happen, and 120 years is very optimistic, even figuring we double the potential reserves with new finds. Any estimates that claim 250 years of coal reserves are either overly-optimistic, or are considering only the United States.
The United States not only has the largest coal reserves in the world (Russia is second), but is mining relatively slowly (though is still the #2 producer). At current rates, the US has a little over 200 years before current reserves are exhausted. Compare that to China, which has the third largest reserves, but is mining almost three times more than the US, meaning that they have only 41 years at current rates. The EU has 51 years. As other countries begin to run out, production in the US might pick up for exports, so it makes sense to analyze this globally.
All of this might be a needless way looking at coal production, because economic factors might be too important for the world to ever end up completely running out of coal. There is the idea of production peaks (see peak oil) for finite resources, where, well before a resource runs out, it climbs to a maximum production, then falls over time until the resource is depleted. Now, the reasons for this are both physical and economic, and honestly beyond me. A peak in coal production may happen well before 2050, followed by anything from a global crisis - if the need for coal stays but supply drops - to no problems - if the world smoothly switches to other forms of energy as production declines. A common estimate for this coal peak is 2025, but predictions vary wildly, and peaks are difficult to predict (I.E. the oil peak may have already happened, but we won't know for sure until we see a few more years of data).
So, regardless of any peak, somewhere between 60 and 80 years of coal is likely available if a major shift is not made in coal usage. But a major shift is what I am concerned about. Oil and natural gas reserves will run out well before coal, so an option to keep in mind, along with other alternatives, is to use coal to replace other fossil fuels, with coal-to-methanol or coal gasification. I might write about them later, but it appears that the numbers don't support these methods. Replacing oil with coal will reduce the reserves of coal faster and still put the year of depletion around the same time for either scenario. It may be worthwhile to discuss these processes from a standpoint of energy independence, so the US could cut down on oil imports, and again, I am ignoring (for now) everything about CO2 emissions. I'll get to some of those topics in another post.