Monday, March 14, 2011

How long until fossil fuels are completely used?

Today, I’d like to explain the reasoning behind the statement I made in yesterday’s post:

“The planet’s fossil fuel resources are finite and on current trends will not contribute much to the earth’s energy demands one hundred years from now.”

This issue requires perhaps more in the way of heroic assumptions than the customary focus of this blog – namely to estimate the cost of solar power.  Some countries have strict standards for reporting mineral reserves, others do not.  In some countries, everything is reasonably transparent, whilst other countries actively seek to hide or falsify information.  Production and consumption figures might be more certain than reserves, but again this is not uniformly true for all countries.

The source for all data in this post is the BP Statistical Review of World Energy (2009).  The word ‘reserves’ is interpreted to mean “those quantities that geological and engineering information indicates with reasonable certainty can be recovered in the future from known reservoirs under existing economic and operating conditions”.

At the end of 2008, world reserves were:

Oil                   1,409 billion barrels (including Canadian oil sands)
Natural gas      185 trillion cubic metres
Hard coal        411.3 billion tonnes (anthracite and bituminous)
Other coal       414.7 billion tonnes (sub-bituminous and lignite)

Consumption rates were:

Oil                   30.83 billion barrels per year (84.455 million barrels per day)
Natural gas      3.019 trillion cubic metres per year
All coal            3.304 billion tonnes of oil equivalent per year

Conversion factors:

1 barrel oil = 0.1364 tonnes oil
1 billion cubic metres natural gas = 6.60 million barrels of oil equivalent
1 tonne hard coal = 0.67 tonnes of oil equivalent
1 tonne other coal = 0.33 tonnes of oil equivalent

On those figures, with current reserves and current rate of consumption, the oil will be gone in 46 years, the natural gas in 61 years and the coal in 125 years.  But that is not the end of the story; we need to consider the overall rate of consumption of energy from fossil fuels.

Assume that when the oil has gone, the energy demand previously met by oil is transferred to natural gas (in addition to the existing consumption).  In turn, when the natural gas is gone, assume all the fossil fuel demand is met by coal.  That gives Figure 1.  The overall rate of energy consumption from fossil fuels is constant, and the resources are gone in 75 years.

Figure 1: Remaining reserves (in Mt oil or oil equivalent) of oil, natural gas and coal.

Since I first made these calculations in mid 2006, reserve estimates for oil have increased somewhat, mainly due to inclusion of 150 billion barrels from Canadian oil sands.  That increase has not really altered the overall conclusions.

As I explained earlier, figures for reserves, production and consumption need to be used with great caution.  Two excellent websites that discuss these issues are The Oil Drum ( and ASPO International, the association for the study of peak oil and gas (  The Oil Drum is a very active site.

So, what does all this mean?

1.      Whilst there will always be another kg or litre of fossil fuels available on Planet Earth, for practical purposes the reserves will be depleted within a hundred years.  Yes, more reserves might be found, which would act to extend the time estimate, but on the other hand consumption rates will also surely go up, at least in the immediate future.
2.      The near-unanimous view of climate science is that consumption of Earth’s fossil fuel reserves will be disastrous.  I accept that scientific opinion.  Two excellent sites that discuss these matters are RealClimate ( and Skeptical Science (  Here, I am explicitly ruling out large-scale implementation of Carbon Capture and Storage, which perhaps I’ll explore in another post.
3.      To preserve our way of life, humankind has to develop new energy infrastructure.  As I explained yesterday, there are strong reasons why nuclear fission should not be a big part of that development.
4.      Sooner or later, we must make the transition away from fossil fuels.   It’s best to do that whilst we still have the chance to mitigate or avoid the worst of anthropogenic global warming.


  1. Well said. Have you done the calculations for atmospheric CO2 concentrations when all the fossil fuels are consumed?

  2. To RJ's Economics Web Page

    Thanks for the suggestion. I'm working on a post about the CO2 concentrations.