All fossil fuels are mixtures of hydrocarbons, which contain varying ratios of carbon and hydrogen. Upon their combustion, carbon is converted into CO2 and hydrogen into water. Consequently, when burned these fuels are irreversibly used up. The increases in the CO2 content of the atmosphere which result from human activities and the excessive combustion of fossil fuel is considered to be a major man-made cause of global warming.
Much has been said of the extent of our available oil and gas resources (see Chapters 4 and 5). Although our coal reserves may last for another two or three centuries, the mining of coal (except in areas suited to surface strip mining) involves difficult and dangerous labor, hazards and environmental difficulties. Moreover, our oil and gas reserves, although readily accessible, will not last much longer than the end of the 21st century - even taking into consideration new discoveries, improved technologies and unconventional sources.
Besides accessible petroleum oil and natural gas (and coal) resources, we have additional unconventional hydrocarbon sources such as heavy oil deposits in Venezuela, oil shale in various geological formations, including the U.S. Rocky Mountains, and vast tar sand deposits in Alberta. The hydrates of methane, as are found under the Siberian tundra and along the continental shelves of the oceans, represent significant resources for natural gas for the future. They too will all eventually be exploited, although the difficulties and costs involved are immense.
Besides the size of the reserves, as discussed, one must also consider the expanding world population, which currently exceeds six billion and will most likely attain eight to ten billion by the end of the 21st century. The consequences of increasing consumption of our reserves, due to improving standards of living in the world, as well as increased demands in fast-developing countries such as China and India, are clear. Potential oil reserves estimated at one to two trillion barrels or some 135 to 270 billion tonnes must be considered when taking into account these factors. The best present estimates of our readily accessible oil reserves imply that they would last for no more than 70 years at the current rate of consumption. Natural gas reserves are somewhat larger, and may last for another 80 to 100 years. New discoveries and improved recovery methods can extend these estimates, while increased oil consumption will place more pressure on our reserves. In any case, mankind must begin to prepare itself for the future, and find new sources and solutions.
In order to satisfy mankind's ever-increasing energy needs, the use of all feasible alternative energy sources will be necessary in the future. Hydro and geother-mal energy are already well used where Nature makes them feasible, but no further major new suitable locations are expected to be found in developed countries. The energy of the Sun, wind, waves and tides of the seas all have great potential and are increasingly being exploited, though their large-scale use as substitutes for fossil fuels is not expected to have significant effect on our energy picture in the foreseeable future.
Perhaps the greatest technological achievement of the 20th century has been mankind's ability to harness the energy of the atom. Regretfully, as this was first achieved in the building of the atom bomb, public opinion has in subsequent years increasingly turned against this energy source, even when considering only its peaceful uses. During the past few decades, relatively few new atomic power plants have been constructed (and none in the United States). There is even strong sentiment in some countries to close them down altogether, whilst other countries such as France depend on them for some 80% of their electricity needs. Much progress has been made to limit the use of atomic energy only to peaceful uses and to improve safety aspects, including radioactive waste storage and disposal. Our society, which was able to build the atom bomb, can - and will - solve these problems. The decline of the atomic energy industry in most industrialized countries is most regrettable and shortsighted. Whether or not one likes atomic energy, it is for the foreseeable future the most feasible and massive energy source available to mankind. Of course it should be made even safer and more effective, solving the problem of reuse and storage of radioactive wastes as well as developing new improved reactor designs and the use of atomic fusion. Conservation, as well as use of alternate energy sources, are most desirable, but these alone cannot solve our enormous appetite for energy. Nonetheless, there have been recent hopeful signs that the generally negative perception of atomic energy is slowly changing.
Despite their non-renewable nature and diminishing resources, fossil fuels -and particularly oil and gas - will maintain their leading role as long as they are readily available. A vast infrastructure exists for their transport and distribution. As transportation fuels for our cars, trucks and airplanes they are used in the form of their convenient products (gasoline, diesel fuel or as compressed natural gas). Natural gas and heating oil are essential for heating our homes and offices, and to provide energy for industry. Oil and gas are also the raw materials for chemical products and materials essential for our everyday life. However, the bulk of the fossil fuels are still utilized in power plants to generate electricity. From whatever source electricity is generated, its storage on a large scale is still unresolved (batteries, for example, are inefficient and bulky), and it is therefore necessary to find, besides new energy sources, efficient ways for energy storage and distribution. We also need to develop new and efficient ways to produce synthetic hydrocarbons and their varied products from non-fossil fuel sources. It is ironic that, in knowing fully that we will need to produce synthetic hydrocarbons at a significant cost and major technological efforts, we continue to burn much of the still-existing natural fossil fuel resources in order to provide energy.
One approach which has been proposed and much discussed recently is the use of hydrogen as a clean fuel (the so-called "hydrogen economy"; see Chapter 9). Free hydrogen is however not a natural energy source on Earth as it is incompatible with the high oxygen content of our atmosphere. Whilst it is indeed "clean burning" (forming only water), its generation from its bound compounds (hydrocarbons, water) is a highly energy-consuming process which is at present far from clean as hydrogen is mainly produced by reforming of natural gas, oil or coal (i.e., fossil fuels) to syn-gas (a mixture of CO and H2). The CO generated is oxidized to CO2, or it can be further used in the water gas shift reaction to yield more hydrogen. Overall, however, one-fourth of the energy of fossil fuels is lost as heat. Hydrogen can also be produced by the electrolysis of water, a process which does not produce CO2 and does not necessarily involve a fossil fuel source. Our oceans represent an inexhaustible source of water that can be split by electricity (or by other means) to produce hydrogen and oxygen. Hydrogen is, however, not a convenient energy storage medium, as its storage, transportation and distribution are both difficult and costly. The handling of extremely volatile and potentially explosive hydrogen gas necessitates high-pressure equipment, the use of special materials to minimize diffusion and leakage, and extensive safety precautions to prevent explosions. In addition to these difficulties, the essential infrastructure for the development of the hydrogen economy is yet to be developed, at extreme cost.
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