I think the 21st century is going to see a return to coal as a major (possibly the major) source of energy for the world. Why? The three most populous countries in the world: China, India and the US have two things in common, not that much oil and lots of coal.
Turns out that there is 4 times as much energy stored in world coal reserves than in oil reserves when measured in BTU. And the US, China and India have the first, third and fourth largest reserves in the world respectively (1, 2).
The US is the Saudi Arabia of coal. Actually the US might even be more that. The Saudis have 261.9 billion barrels of proven oil reserves (3). The United States has coal reserves in the region of 280,000 million short tons, which is about 1,204 BBOE (billion barrels of oil equivalent) . So the US has over 4.5 times as much energy stored in our ground as the Saudis have in theirs.
Now, while I think that is the way the world is headed, the question is is that a good thing?
On this question I am ambivalent.
Coal can be turned into a liquid fuel using the Fischer-Tropsch process to replace gasoline or diesel at around $35 barrel of oil equivalent(4). The Governor of Montana is pushing for the US to do more of this. It also can be used to create electricity which could power a plugin hybrid. And creating ethanol in its current stage uses a lot of coal, as each gallon takes .64 gallon of oil equivalent in coal (5). All of these would reduce the amount of demand that China, India and the US have for oil imports.
Reducing the demand for imported oil would be a good thing, as China has overlooked Darfur in order to get some oil, India deals with Iran in order to get theirs and the US supports the Saudi regime. I have written many times on the oil curse, so decreasing oil would be good.
On the other hand, coal is ugly. First, it is dangerous to mine, as the deaths in West Virginia, and the ones continually coming out of China show us. Second, it is bad for the environment. The mining can remove entire mountains or dig underneath them. It leaches all sorts of gunk into the surrounding rivers and ground water. Third, it gives off more carbon, and therefore more greenhouse gas CO2, per BTU of energy than either oil or natural gas. Fourth, when burned in an electricity coal plant, it gives off lots of air pollutants including: nitrous oxide, sulfur oxide and mercury.
There are efforts underway for clean coal. This would dramatically reduce the amount of air pollution. There are many ways they are looking into to sequester the carbon dioxide. But, none of this will be prime time for probably 5-10 years, and it would take 20+ before it could be rolled out to most of the coal plants.
If I was forced to choose between the US, China and India importing oil from unsavory countries or having them use domestic but dirty coal, I think I would go with the coal, but at the same time be investing in R&D for clean coal and other cleaner and more renewable forms of energy.