First of all, we know that fossil fuels will run out. They are a limited resource. The bad news is that they will run out way sooner than anyone thinks – by 2070 at most. I’m not going to prove it to you. I’m going to show you how to prove it to yourself and anyone else you talk to. But if that is the case, it requires we change our approach.

The estimates we hear about how long the fossil fuels will last – such as the one: “We have enough coal to last 300 years..” Which you may have heard or seen, all include the phrase: “At current rates of use.” But we know that isn’t true. The population in the world is increasing, and we are all increasing our use of energy with more electronic gadgets and cars and planes and boats, and China and India are getting more affluent and buying more things, so the rate of energy use worldwide is increasing. Five years ago when I first did this analysis, the rate of energy use was increasing 1.7 percent per year. This year, the British Petroleum company analyzed energy use last year, and determined that coal use increased 5.5 percent over the year before. If we take the amount of estimated recoverable fossil fuels, and then subtract the amount used each year, we can get an estimate of when they will run out. BP now estimates we will run out of recoverable coal worldwide in 55 years.

You can show this to yourself with a simple spreadsheet and data from some different official and trusted sources. I use the British Petroleum company (bp.com), The US Department of Energy (doe.gov), And the World Coal Association figures.
They estimate that there are about 948 billion tons of recoverable coal in the world and that last year, the world used about 7,678 million tons of coal. If you divide it up, that leaves about 123 years of recoverable coal at current usage rates. When I was a kid, they estimated at least 400 years worth of coal at the then usage rates.

But usage is increasing! If you use the 1.7 percent increasing usage, and subtract the usage from the reserves each year, you get that coal will run out in 50 years – at about 2077.
If you use the rate of 5.5 percent, it runs out in about 35 years – in 2048.

Make your own spreadsheet. Put a cell in for current estimated reserves. Put one in for current usage. Put one in for percent of increase ( or decrease). Remember that increase of usage is a usage rate of 1 plus the percent (.0whatever), so that an increase of 1.7 percent gets translated to a rate change of 1.017 as a multiplication factor.
Make these as separate cells so you can change them and see the effects reflected through the entire spreadsheet.

They estimated there were 948 billion tons of recoverable coal in the world. The world usage was 7,678 Million tons and the increase was 5.4 percent over 2010.

Make a row across the page of years from 2011 to 2100.
Under 2011, put the phrase: “=B4”, to refer to the figure for the reserves.
Under that, put the phrase: “=B5”, to refer to the figure for the usage that year.
Under that, put the equation: “=B4-B5”, to calculate the amount left in the reserves.
Now,
Under the year 2012, put the phrase: “=C12”, to bring up the remainder from the year before.
Under that, put the phrase: “=C11*$B$6”, to calculate the usage for that year as an increase from the usage of the previous year.
Under that, put the phrase: “=D10-D11”, to calculate the remainder.

Now, copy those last three cells (D10, D11, and D12) and paste them out in every cell out to the last cell under the year 2100.

At a usage increase of 1.7 percent per year:

At 5.5 percent per year