Love or hate it, oil is an incredibly useful product.

Used to create everything from plastics to pharmaceuticals--and of course, fuel for transportation--its environmental credentials might be low, but it's been an essential substance in creating the world we live in today.

So too have other energy sources, such as gas, coal, and uranium. But just how much--or little--do we have left to keep us going over the next century?

It's a subject of huge debate, and one covered in great detail in a feature published by the McClatchy Newspapers chain.

As with many other resources, oil, coal, gas and other energy sources are subject to the laws of supply and demand. Our major issue is knowing exactly how much supply we have remaining--and how much each product will be in demand over the coming decades.

Half a century

The figures quoted by some research groups don't make for easy reading. The Energy Information Administration's 2011 outlook suggests the world has 126 years of coal remaining, and only 60 years of gas. Using the Oil & Gas Journal's 2011 figure of 1.47 trillion barrels of oil remaining, at current use there are only around 46 years of reserves left.

Worse still, these figures aren't subject to annual growth in consumption--predicted between a conservative 1.6 percent, and the 2.2 percent rate of past decades. At 1.6 percent, oil, natural gas, coal and uranium could run out within 56 years. At the higher growth rate, liquid fuels could be exhausted in 36 years--based on current estimates.

On the flip side, new reserves are being discovered all the time, and in the past this has kept pace with usage.

Finding new resources will undoubtedly begin to get more expensive, but that's just the price we'll have to pay to ensure our reserves last beyond the next half century.

The U.S. Geological Survey estimates that total undiscovered reserves amount to 681 billion barrels. This includes reserves deemed too expensive to access--and half of that amount would only satiate global demand for another decade.

Action coming too late?

Some feel the Obama Administration's 54.5 mpg 2025 CAFE requirements have come too late--that countries such as the U.S. should have started buying more efficient cars decades ago. Even then, countries like China and India are bumping up demand--and contributing hugely to global pollution as they do so.

Others suggest the figures for remaining reserves are still pessimistic, that they don't take into account advances in technology allowing us to more efficiently drill for oil, or frack for gas. Again, it's unclear whether even those figures take into account a projected 1.7 billion increase in global population by 2035, with 850 million more cars.

It's a debate that will rumble on for some time to come, and nobody is quite sure just how long we have left of some of our most convenient energy sources.

Energy shortage is of course one of the best reasons for increasing focus on whichever renewable sources are most appropriate for any given environment, too. It's still yet to happen on a large scale, but over the next few decades renewable energy may prove vital for taking the pressure off our fossil fuel addiction.

But one thing is for sure--nobody is too keen to find out what happens when we run out...


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