This is not about how horribly polluting coal is. It’s not about how dangerous coal mining is. It’s not about how much it contributes to carbon emissions and thus to global warming.
No, this is to fight the meme that coal is plentiful.
If you consider a linear growth in demand for coal, the average demand over 2005-2050 will be 2.5 times current demand, which means that we’ll have used 112 of these “reserve-years”, and, at 4 times current production in 2050, we’ll have about 10 years left of reserves worldwide at that rythm of production (not even considering if these reserves will actually be accessible and usable at such rates).
The same calculation for the USA, if you consider that demand for coal on current trends (+71% between 1975 and 2005) is roughly set to double, would lead to conclude that in 2050, at those then prevailing rates of production, the USA would still have 90 years of coal reserves.