Natural Gas
Natural Gas
Introduction
Natural gas is the cleanest of conventional fossil fuels. When burned, the colorless, odorless gas emits 30% less carbon dioxide (CO2), the most important anthropogenic (human-caused) greenhouse gas, than does oil, and 45% less CO2 than coal. Natural gas also releases significantly less particulate matter, nitrogen oxides, and sulfur dioxides (which can cause acid rain) than other fossil fuels. Even so, it accounts for a significant fraction of global greenhouse gas emissions. Nearly 21% of the 31.1 billion tons (28.2 billion metric tons) of CO2 pumped into the atmosphere by countries around the globe in 2005 came from the consumption and flaring of natural gas.
Natural gas itself—composed primarily of methane, is at least 21 times more potent at heating the planet than CO2. It also contributes to global warming directly when it escapes from pipelines, wells, and processing facilities; is vented from coal mines for worker safety; or makes its way into the atmosphere because of equipment failure. The natural gas industry is responsible for approximately 15% of anthropogenic methane emissions.
Historical Background and Scientific Foundations
Natural gas and oil are both the product of prolonged heat and pressure acting on the remains of tiny oceanic plants and animals (plankton) that were buried deep under sand, silt, and rock some 200–400 million years ago. Natural gas can also be extracted from coal seams. Coal bed methane is a hazard to working coal miners, as the highly combustible gas can cause underground explosions. Today, it is being considered as a useful energy resource.
Around 500 BC, the Chinese were the first to harness natural gas as fuel, using bamboo to pipe it from seeps in order to boil and desalinate seawater for drinking. However, natural gas was not a widely important source of energy until after World War II (1939–1945), when advances in metallurgy, welding, and pipe rolling allowed for the construction of reliable pipelines and widespread distribution of the gas. New uses in the residential, commercial, and industrial sectors proliferated. Since the 1980s, natural-gas-fired power generation and other gas uses have grown more rapidly than before, in part because natural gas generally has lower investment costs, higher fuel efficiency, better operational flexibility, and lower toxicity than other conventional fossil fuels.
As of 2005, natural gas accounted for about 21% of global primary energy use. Industry—where natural gas is used both as an energy source and as the base ingredient for fertilizer, plastics, fabrics, and other products—is the greatest consumer of natural gas, accounting for 43% of natural gas use across all sectors.
Impacts and Issues
Because natural gas emits the least greenhouse gas per unit of energy among conventional fossil fuels, its expanded use is often favored as an economically practical way to begin reducing human greenhouse-gas emissions and as a bridge to cleaner technologies. For example, replacing coal-fired power plants with gas power plants could approximately halve the amount of CO2 produced per unit of electricity, and carbon sequestration technologies in the future may help natural gas power become even cleaner.
Hydrogen (H2), a clean-burning gas that in theory could serve as an emission-free fuel, is currently produced primarily from natural gas. However, more CO2 is produced by making H2 from natural gas than by burning the natural gas directly; substituting H2 for natural gas can make greenhouse sense only if carbon is sequestered at the refinery or if H2 is consumed in high-efficiency fuel cells rather than being burned. Natural gas can also be a relatively clean way to make some renewable energy sources more reliable by filling power-generation gaps left by intermittent power sources such as wind turbines and solar panels.
WORDS TO KNOW
ACID RAIN: A form of precipitation that is significantly more acidic than neutral water, often produced as the result of industrial processes.
ANTHROPOGENIC: Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.
CARBON SEQUESTRATION: The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen, and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned.
CARCINOGENS: Chemicals that induce, or increase the likelihood of, cancer. Carcinogens may be natural or artificial, and may have a carcinogenic effect in low or high concentrations, depending on the chemistry of the particular substance.
FOSSIL FUELS: Fuels formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.
GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.
RENEWABLE ENERGY: Energy obtained from sources that are renewed at once, or fairly rapidly, by natural or managed processes that can be expected to continue indefinitely. Wind, sun, wood, crops, and waves can all be sources of renewable energy.
Expanding natural gas extraction to meet new demand carries its own set of problems. The fossil fuel is not an inexhaustible resource and its production will eventually peak. In rich gas fields in Alberta (Canada) and Texas, for example, gas production has remained
relatively stable or declined in recent years, even though the number of gas wells drilled per year has gone up. The decline of domestic production in countries that rely on natural gas is a major issue, as the fuel is costly and energy-intensive to import from overseas as a liquid. However, this method is expected to expand to meet growing global energy needs.
Meanwhile, increasing demand, a decline in the productivity of many conventional natural gas deposits, and a sharp increase in natural gas prices have led companies to pursue unconventional deposits of natural gas, such as tight sands and coal bed methane, that were once considered too costly and difficult to extract. This is primarily occurring in the United States and Canada. Drilling for these types of gases has increased in the Rocky Mountains over the last decade, and the associated latticework of bulldozed well pads and roads, increased heavy truck traffic, and storage ponds (which often contain salty or chemical-laden water) can harm wildlife, livestock, habitat connectivity, and air and water quality. The chemicals in drilling wells, some of them potent carcinogens, may pose health risks to those living in neighboring rural communities. Another form of unconventional natural gas, methane gas hydrate ice found on the ocean floor, is still out of reach, as no safe or economical methods of extraction are yet available. Indeed, this resource may be too dispersed and difficult to access to ever be environmentally and economically feasible.
See Also Energy Contributions; Hydrocarbons; Methane.
BIBLIOGRAPHY
Books
Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.
Periodicals
Hoffert, Martin I., et al. “Advanced Technology Paths to Global Climate Stability: Energy for a Greenhouse Planet.” Science 298 (2002): 981–987.
Maffly, Brian. “Where the Antelope (and the Oil Companies) Play.” High Country News (August 18, 2003).
Pacala, S., and R. Socolow. “Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies.” Science 305 (2004): 968–972.
Web Sites
“Environment: Energy-related Emissions Data & Environmental Analysis.” Energy Information Administration, 2007. <http://www.eia.doe.gov/environment.html> (accessed November 8, 2007).
“Global Anthropogenic Non-CO2 Greenhouse Gas Emissions: 1990–2020.” U.S. Environmental Protection Agency, 2006. <http://www.epa.gov/nonco2/econ-inv/downloads/GlobalAnthroEmissionsReport.pdf> (accessed November 10, 2007).
“Overview of Natural Gas.” NaturalGas.org, 2004. <http://naturalgas.org/overview.asp> (accessed November 8, 2007).
Sarah Gilman