Most of the natural gas produced is trapped in rock formations that are millions of years old and at depths much deeper than the shallow-biogenic type. The market for natural gas has developed recently, relative to the history of the oil industry. For many years, it was regarded as a nuisance because necessary pipelines did not exist and could not be justified financially. Therefore, discoveries of gas in the search for oil were abandoned, and when gas was produced as a co-product from oil wells, it was ignited and flared for safety reasons. Natural gas is now regarded as a valuable commodity and only minor amounts are flared or lost to the atmosphere. Markets have developed and demand is strong and growing. The primary transportation of natural gas is by pipeline, and because of higher prices, smaller deposits of gas can justify drilling and laying a pipeline. In addition, a rapidly-developing transportation mode for natural gas is by tanker in liquefied form. Large volumes can be pressurized and moved on the high seas to coastal terminals where pipelines then move the gas to consumers. Natural gas is now a global commodity.

The increased value also spurs exploration for new deposits at depths of 4 mi. (6.4 km.), and the development of nontraditional sources, such as from landfills and coal seams. The production of natural gas from coal beds, known as coal bed methane, is through wells drilled into the coal. This same gas has been the source of coalmine explosions when not properly ventilated. The production of coal bed methane can reduce the eventual release of methane to the atmosphere through mining operations. The production of natural gas from hydrates is not a reality yet, for technical and economic reasons. Ironically, the methane in gas hydrates of tundra regions may be released by global warming. The permafrost is thawing in some areas. This will release the gas trapped in ice crystals to the atmosphere. In this instance, global warming becomes the culprit in creating greenhouse gas.

Most of the methane in the atmosphere is the result of living organisms such as livestock, and not natural gas. Natural gas is sequestered in the Earth until released through production into a pipeline or other vessel. It enters the atmosphere in raw form or as CO2 and nitrous oxide from combustion. While the greenhouse gases released are in lesser amounts than from burning other hydrocarbons, the concern is for the enormous volumes of natural gas being produced and, therefore, the enormous amount of CO2emitted. Natural gas has been forming for millions of years; the first organisms on Earth are thought to be more than 600 million years old. These organisms, if buried before decay, can generate natural gas through a maturation process in the absence of oxygen. If not buried, they oxidize in the atmosphere and release gases at that time. The natural gas produced today literally represents a deposit of greenhouse gas that was not spent at the time the organism died. So, millions of years of saved deposits of greenhouse gas are now being released at a rapid and accelerating rate with the popularity of natural gas as a clean, efficient burning fuel.

Based on trapped gases in ice cores in Antarctica, there has been a dramatic increase in greenhouse gases in the global atmosphere since the beginning of the Industrial Revolution. Samples indicate that in the last 200 years, CO2 has increased by 35 percent, methane by 600 percent, and nitrous oxide by 18 percent. Data for CO2 suggest that about 100 years ago there was an increase in the growth rate of atmospheric concentration, followed by another rate increase beginning about 50 years ago, when the world consumption of hydrocarbons, combined oil and gas, surpassed coal in energy content.

See ALSo: Carbon Dioxide; Carbon Emissions; Coal; Greenhouse Gases; Oil, Production of.

BIBLIOGRApHY. Carbon Dioxide Information Analysis Center, (cited November 2007); Nick Hopwood and Jordan Cohen, "Greenhouse Gases and Society," University of Michigan, (cited November 2007); Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, 2007).

Roger Brown Western Illinois University

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