Fossil Fuels
Fossil fuels or mineral fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. These fuels contain high percentages of carbon and hydrocarbons.
Fossil fuels range from volatile materials with low carbon:hydrogen ratios like methane, to liquid petroleum to nonvolatile materials composed of almost pure carbon such as anthracite coal. Methane can be found in hydrocarbon fields, alone, associated with oil, or in the form of methane clathrates. It is generally accepted that they formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust.
In 2007 the UK primary sources of energy consisted of oil 38%, coal 16.7% and natural gas 37.7%. Nuclear power (5.8%) and renewable sources (1.8%) make up the total energy usage. The dependence of the UK on fossil fuels at that time is clearly shown by these 2007 totals.
Burning fossil fuels globally produces around 21.3 billion tons (21.3 gigatons) of carbon dioxide per year, and it is estimated that natural processes can only absorb about half of that amount. There is a net increase of 10.65 billion tones of atmospheric carbon dioxide per year (one tonne of atmospheric carbon is equivalent to 44/12 or 3.7 tons of carbon dioxide).
(US Department of Energy on greenhouse gases)
Carbon dioxide is one of the greenhouse gases that enhances radiative forcing and contributes to global warming, causing the average surface temperature of the Earth to rise in response, which climate scientists agree will cause major adverse effects.
Effects of CO2
Carbon dioxide (CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere as a gas.
Within the atmosphere it is currently at a globally averaged concentration of approximately 387 ppm by volume, although it does fluctuate slightly throughout the year.
Carbon dioxide is used by plants during photosynthesis to make sugars which may either be consumed again in respiration or used as the raw material to produce polysaccharides such as starch and cellulose, proteins and the wide variety of other organic compounds required for plant growth and development.
But it is also produced during respiration by plants, and by all animals, fungi and microorganisms that depend on living and decaying plants for food, either directly or indirectly.
Carbon dioxide is a greenhouse gas, which means that it transmits visible light but absorbs strongly in the infrared and near-infrared.
Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay.
Carbon dioxide is also generated as a by-product of the combustion of fossil fuels or the burning of vegetable matter, among other chemical processes. Large amounts of carbon dioxide are emitted from volcanoes and other geothermal processes such as hot springs and geysers and by the dissolution of carbonates in crustal rocks.
Sustainable energy sources may also include technologies that improve energy efficiency.
(US Department of Energy on greenhouse gases). http://www.eia.gov/oiaf/1605/ggccebro/chapter1.html