If energy is all around us (in the forms of heat, molecular movement, light, sound, etc.) why should we be concerned about energy prices and a future energy crisis? Low quality energy is not intense enough or too dispersed to perform much useful work (like generate electricity). Heat and dispersed geothermal energy in the earth would be examples of this. Moderate and high quality energy sources are concentrated enough to perform many types of useful work. Are these sources practical sources of energy for human needs? Not necessarily--that depends on the net energy ratio which is the energy produced compared to the energy used to produce it. Finding, processing, concentrating, and transporting an energy source may use more energy than the amount which id produced.
As the graph below indicates, humans have tended to use more and more energy per person as time has progressed.

In Prehistory, humans probably had a daily per capita energy consumption of about 2,000 kcal. By 1400 it was approaching 30,000 which is the level in many developing nations today (American Chemical Society, 1994). By 2000, the average per capita energy expenditure is 250,000-300,000 kcal (Kemp, 2004). Although there are many people on earth who lack the means to use considerable amounts of conventional energy, that situation is changing. Two billion people in the developing world do not have access to commercial electricity but the demand for electricity in developing nations is growing much faster than in the rest of the world (Kemp, 2004). The Department of Energy predicts that the world's energy use will increase 58% by the year 2025. China's energy demand alone grew 6% during the year 2001-2002 (Blatt, 2005). Energy is an important issue in the United States because of the enormous amount of energy we use. The U.S. population makes up 4.8% the world's population but uses 25% of the earth's energy resources (Americans use more energy for air conditioning than the population of China uses for all purposes). In contrast, India has 16% the world's population and uses 1.5% the world's commercial energy. As the graph below indicates, the average American uses much more energy than the vast majority of people living in the world.

There are many different energy sources which have been used in the United States. The relative percentages of these various energy sources in the total energy use has changed over time. In early America, wood was the primary source of energy. The contributions of coal to the total national energy usage were greatest around 1900. Since then, oil and natural gas have become the most significant sources of energy in this country.

(American Chemical Society, 1994).

1) FOSSIL FUELS
As discussed previously, plants absorb energy from the sun and store some of it in chemical bonds. If this energy is not released during decomposition because it is buried (and thus protected form oxygen), the potential energy remains. As of 2007, the greatest source of carbon dioxide emissions and the most rapidly increasing source was the generation of electricity (IPCC, Document III, 2007).

A) COAL

America possesses the largest coal reserves in the world, accounting for 26% of the world's coal consumption. Coal generates 52% of American's electricity and 66% of the energy use in China (Blatt, 2005). The following photo is of a series of train cars transporting coal.

Millions of years ago, the earth's temperature was warmer and large land masses covered the equator. The large amounts of plant biomass was produced and much of it was buried before it could decompose. Fossil beds commonly contain at least a little coal; most coal came from 300 million years ago when the climate was warmer and wetter. This compost was compressed and heated over time to go through several transitional stages as oxygen and moisture were gradually lost:
a) Peat does not burn as well as wood.
b) Lignite (brown coal) is the lowest grade of coal, similar in chemical composition and energy potential to wood. Some have asked the question whether lignite is "low quality coal or high quality dirt."
c) Bituminous coal is the most common form of coal. It burns well (with twice the energy content of lignite) although it produces a good deal of smoke and has a high sulfur content.
d) Anthracite coal is almost pure carbon and is the most desirable form of coal.

The following plant is one in which coal is converted to electricity.

In 1850, coal provided 10% the energy in the U.S. (wood supplied the rest); 50 years later, coal provided 70% of the U.S. energy but this dropped to 23% by 1990. Coal is the most abundant fossil fuel. World coal supplies could supply earth's energy needs for perhaps 200 years since coal reserves are 20-40x greater than those of petroleum. North America and the former USSR each have 11-13% world's coal reserves; China has 57%. About 60% of the world's coal (and 70% of the coal in the U.S.) is burned to produce steam to make electricity. More than half of the U.S. electricity is produced this way (American Chemical Society, 1994)..

Disadvantages of the use of coal:
1) MINING
Since 1900, more than 100,000 workers in the U.S. have died in explosions, floods, collapsing tunnels, and suffocating gases. More than 1 million workers have been disabled; 250,000 suffer from black lung disease (a form of emphysema). Taxpayers now pay $1 billion/year in benefits to these retired workers who suffered due to inappropriate safety measures of the past. About 1/3 present tunnel mines still present a high risk for black lung disease.
Strip mining is the only alternative to tunnels. It does not present the health risks to coal miners seen in tunnel mining but it leaves craters and often acidifies soils and water. Erosion in areas which have been strip-mined is increased 1000x and toxic materials are leached and contaminate surrounding groundwater. More than 1 million acres in the U.S. have been destroyed by strip mining and not reclaimed.
2) SMOKE
Bituminous coal releases as much smoke as heat; old London and Pittsburgh were smoky, grimy places. Bituminous coal also contains sulfur which produces acid rain when released into the atmosphere. Coal burning releases 70% U.S. sulfur dioxide emissions and 1/4 nitric oxide emissions. The U.S. burns 900 million tons of coal (83% of this is used for electricity); this creates 18 million metric tons of sulfur dioxide, 5 million tons of nitrogen oxides, 4 million tons of particulates, 0.6 million tons of CO and VOCs (volatile organic carbons) and a trillion metric tons of carbon dioxide.
There have been efforts to make coal-burning cleaner. Fluidized bed combustion boilers use limestone to remove 90-98% of the sulfur, producing solid calcium sulfate which will not be released into the air. Coal can be converted to methane, methanol, or synthetic gasoline, all of which are cleaner burning & easier to transport; due to the energy needed to create these substances, they are not yet economical for widespread use (currently around 3x price oil).