According to the BP's 2006 Statistical Review of World Energy, "proven reserves" of energy in the world totalled about 809 BTOE (Billion Tons of Oil Equivalent).  Last year, BP reported we had 806 BTOE left, and we used 9.2 in fossil fuel, so the good news is we discovered 12.2 in new fossil reserves, which is slightly more than we used.

A single BTOE is a huge amount of energy - It's what the US goes through in about five months, but the world is using up 11 in Primary Energy a year (and growing every year) so it doesn't take a rocket scientist to figure out that, while it may not be imminent, our fossil fuel supply will most likely not last until the end of the century. 

Of course, the reliability of reserves statistics is somewhat dubious.  Some countries (Saudi Arabia, Kuwait, etc...) are extremely secretive about even their known reserves and the status of existing fields, and educated guesses are about all that can be provided.  Remarkably, they may also purposely avoid further exploration in potentially promising fields to avoid disrupting global prices.  Other countries or companies may misrepresent their statistics up or down for political or economic reasons.  Also "proven" reserves excludes undiscovered supplies of fossil energy, which may be vast according the the EIA and USGS.  The best statistics possible arise when one publically traded energy company buys another - but with the latest cycle of mega-consolidation, those days may be over.  Finally, and depending on the marker price for energy and development of new extraction technology, certain non-traditional sources of fossil fuel may become feasibly and economically exploitable.

Then again, exhaustion of fossil fuel supplies is one thing to be concerned with in the "far" future - but the relative scarcity of the global production rate to the global demand is another.  In other words, we live in a world with a growing population that is increasingly prosperous and hungry for energy (and getting ready to introduce several billion people to the energy-intentive-lifestlye), but the production rates out of individual mines or fields tend to peak and significantly slow down long before the resource is depleted.  A rapidly increasingly demand for any good combined with shrinking capacity to delivery an annual supply will necessarily result in substantial price rises of that good.  So the key question is, given the statistics, how serious a situation do we face?  (See Next Blog Entry!)

The BTOE Breakdown is as follows: High Rank Coal - 320, Low Rank Coal - 145, Oil - 165, Natural Gas - 180.  Assuming we dont discover significantly more "cheap" carbon-based fuel and using the EIA's CO2 coefficients for each fuel type, that comes to 2550 GT (Billion Metric Tons) of Carbon Dioxide left to emit from fossil fuels.  I suggest that 3000GT is a decent estimate to accomodate for additional discoveries.

I submit that we will burn and emit practically all of this before well before the year 2100 Even If we take Extreme action with regards to conservation and emissions control.  So where will that put us in terms of CO2 centration in the air?  There is not good agreement as to how to answer that question with precision.  However, we can VERY ROUGHLY say that as of lately, the world emits 28 GT of CO2 from fossil fuels annually and concentrations go up an average of 2 parts per million. Given that we're presently at around 386 ppm we can estimate that 600 ppm is a probably upper limit as opposed to many extreme scenarious considered by the IPCC and promulgated by certain groups.