Ultimately, all of the world’s energy resources can be traced back to nuclear energy and, to a very small extent, gravitational energy. Gravity determines the rotation of the moon around the earth and causes the tides of the oceans. Some tidal power plants make a very small contribution to energy production, but nuclear reactions – inside the sun or inside the Earth – generate the lion’s share of our energy. Nuclear fusion within the sun is responsible for all of the solar energy that Earth receives, and nuclear fission within the interior of the Earth maintains its temperature of 7000 K. One can think of the sun as a nuclear fusion reactor and the Earth’s interior as a nuclear fission reactor, see the Nuclear Energy page. The supplies of these energy resources will last billions of years. However, the children of today may experience in their lifetime the exhaustion of the major sources of energy that we currently use.
The word fossil (from the Latin fossilis) was introduced by Georgius Agricola, known as the father of mineralogy. He was a student in Leipzig, Germany, from 1514-1518, and published his famous work De Natura Fossilium in 1546. Fossils are artifacts from the geological past (ten thousand to a billion years ago), created from the breakdown of dead plants and animals. Our current gas and oil deposits are a billion to 100 million years old. Coal originated 500 to 100 million years ago, and brown coal arose in the period of time 100 to 10 million years ago.
With the natural resources oil, natural gas, coal, and uranium, a distinction is made between reserves and resources. For the natural resources oil, natural gas, coal, and uranium, a distinction is made between reserves and resources. Reserves represent that part of resources which are commercially recoverable, while contingent resources and prospective resources are less certain, because some significant commercial or technical hurdle must be overcome prior to there being confidence in the eventual production of these quantities. However, several definitions exist. A resource/reserve classification for minerals is given by the U.S. Geological Survey.
Oil reserves grow as new sources are constantly discovered. But it is estimated that now the Earth’s stores of fossil fuels are about half empty. Volumes of oil are measured in units of barrels throughout the world. A barrel of oil corresponds to 42 U.S. gallons or 158.987 liters. The old barrel was a hollow cylindrical container made of vertical wooden staves and bound by wooden or metal hoops. For comparison the U.S. beer barrel is 31 U.S. gallons, while a wine barrel is 31.5 gallons.
At the end of 2012 and 2013, proven world oil reserves were 1687.3 and 1687.9 × 109 barrels, respectively, see BP. The U.S. reserves were 35 × 109 barrels, and the world consumed 31.7 × 109 barrels in 2013. If consumption continues at this rate, world oil reserves will be depleted in this century.
Depletion of conventional natural gas supplies is expected towards the end of this century. The explored reserves have increased from 126 × 1012 m3 in 1990 to 193 × 1012 m3 in 2013. However, consumption has doubled worldwide and in 2013 was at 3.37 × 1012 m3, see BP. According to BGR, world reserves of conventional natural gas are 193 × 1012 m3 and resources are 318 × 1012 m3 at the end of 2013. About 100 × 1012 m3 were already depleted.
BGR analyzes hard and soft varieties of coal, which we will consider together here. In 2013, consumption worldwide was about 8 billion tons (8 × 109 t). Reserves of 968 × 109 t and resources of 22 089 × 109 t are estimated. The annual consumption of coal may increase significantly when oil and natural gas run out. The stocks, however, will last well into the next century.
The distinction between reserves and resources of natural uranium stocks is quite simple: reserves cost less than 80 USD per kg uranium to produce, while resources cost more than this. From a BGR study of global uranium consumption, about 60,000 tons of uranium are consumed annually worldwide. The current reserves are 1.2 × 106 t and will last for a few decades. Resources with a price of less than 260 USD per kg are estimated at 13.4 × 106 t. Even with a price of 260 USD, thermal nuclear power plants will probably continue to be operated into the next century. Another possible source of uranium is sea water, as it contains natural uranium at a mass fraction of 3 × 10−9, but recovering this uranium does not make economic sense. More likely is the use of a fast breeder reactor for substantially more effective utilization of natural uranium. This has significant environmental risks, but it could delay the depletion of uranium sources for a long time.