- Annemarie, Wheaton, IL
I hate to give the "engineer's answer" to this question, but the real answer is....
It depends.
Plenty of factors go into determining the total amount of fossil fuel left in the earth...otherwise known as "reserves". There are three levels of reserves:
Proven reserves (subdivided into developed and undeveloped) - these represent known, accessible, and developable reserves that require nothing more than current equipment and strategy.
Probable reserves - unproven reserves that have a 50% probability of being developed at some time.
Possible reserves - unproven reserves that have a 10% probability of being developed at some time.
You can add to this unknown reserves, which would cover those reserves for which we cannot classify probability.
The best way to keep track of the remaining reserves is to know the following:
1. The current proven reserves.
2. The amount of new reserves that will be discovered.
3. The rate of usage.
Organizations like the International Energy Agency and the US Energy Information Administration do regular analysis on reserves to aid nations in planning. The information comes from energy companies and agencies that do surveys. This is helpful to both establish 1. above, and to get a good handle on 2. We can never perfectly plan how much new reserves we will find in any period of time, but historically, we can trend and come up with a good estimate.
The rate of usage proves most difficult to nail down. The simplest method to use takes the trend of current world energy use and extrapolates forward. According to the World Bank's World Development Indicators, total world energy use has increased slowly over the past decades. The following graph shows world energy use per capita as well as the energy use per capita for several countries.
However, the developing world is looking to move quickly toward the developed quality of life, and with that comes more energy use. One of the questions we must ask is whether we want that development to match our energy use. Do we want to see energy use per capita more like that of the UK, or do we think it should be more like Qatar? I have looked at three scenarios to determine the best guess as to how much available fossil fuels remain and how long we will have them available to us. This analysis has the following assumptions:
1. That new reserves are found at a rate equivalent to 23% of the energy used. This held true for 2001-2010, so we can reasonably assume it fits. Assuming this way also ties the finding of reserves to the usage and transitively the cost. As usage goes up, costs go up, and money available for exploration goes up - making it easier to increase reserves. As usage goes down, the scenario reverses.
2. That countries use fossil fuels at a rate of about 80% of total energy use. The World Bank's World Development Indicators shows this to be a fairly consistent trend over the years. If fossil fuel prices become so high that nations switch to other forms, then that could shift the analysis, but for our purposes, it is a reasonable place to start.
3. The dates resulting from the analysis show a calculated timeframe when proven reserves would be tapped based upon current patterns. It does not prognosticate when those reserves would be tapped.
4. World population continues to increase according to US Census Bureau projections leveling off sometime after 2050, but reaching a little over 9 billion people by then.
5. The use of a specific fuel for a specific activity is left out of the analysis. We assume that as one dries up, we will switch seamlessly to another to perform the same task. In this way we can look at the total usage of fuel instead of performing analysis by fuel. This will actually result in a slightly shorter timeframe of availability, but a more stable one. If we run out of petroleum and have no way to switch to liquid forms of coal or natural gas, then that would create a catastrophic event, which this analysis ignores.
The following shows the trend of reserves and calculations from 2000-2010:
Using the energy use data from the World Bank, multiplying it by the population trends, and extrapolating under three different scenarios, we get the following:
If world energy use continues on its current path, and we find reserves at the same rate we have over the last decade, current reserves will last us until 2082. If world energy use reaches levels in the UK (per capita) today, then we have until 2066. If the world increases its usage rate to that of the US, then we have until 2048. This ignores the environmental consequences of burning that much energy in that period of time.
One final note on US energy use, as the following bar chart shows, our average is not homogenous. As a country that contains within it several of the world's largest economies, we still have not settled on a national policy for energy use. The number used in the assessment above reflects the average usage, but we can still sway towards that of Texas (40-50% higher than average) or towards California and New York (30-40% lower than current average). As the world's largest energy user, we have a big choice to make.
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