Greenhouse gases (Encyclopedia of Environmental Issues, Revised Edition)
The majority of scientists accept that a small global warming has taken place—that is, the earth’s surface temperature has warmed about 0.7 degree Celsius (1.3 degrees Fahrenheit)—since the end of the nineteenth century. At least half of this temperature rise is attributed to the release of greenhouse gases into the atmosphere by human beings. It is thought that if greenhouse gases were returned to their 1990 levels, the temperature would still rise another 0.5 degree Celsius (0.9 degree Fahrenheit). Since greenhouse gases are transparent to visible light, sunlight passes through the atmosphere and warms the earth’s surface. The warmed surface radiates infrared into the sky, where greenhouse gases absorb infrared and then reradiate it. They radiate about half of the infrared upward into space and half of it back down to the earth’s surface. Since the earth absorbs more energy than it radiates back into space, it heats up until the energies entering and leaving are equal. Balance is possible because a hotter earth radiates with greater intensity and at shorter wavelengths where greenhouse gases allow more infrared to escape into space.
Water vapor strongly absorbs infrared of about 3 microns wavelength (3,000 nanometers), and so does carbon dioxide. Adding more carbon dioxide will not change the amount of energy passing out into space, since water vapor absorbs all of the energy near that wavelength. However, more carbon dioxide...
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Earth’s Major Greenhouse Gases (Encyclopedia of Environmental Issues, Revised Edition)
Water vapor, carbon dioxide, methane, nitrous oxide, fluorocarbons, and ozone are the major greenhouse gases. The effect of a particular gas depends on which other gases are present, how much of the gas is present, and how likely a gas molecule is to absorb infrared radiation.
Water vapor is the most important greenhouse gas, but human activities have no direct effect on the global average amount of water vapor, which is fixed mainly by evaporation from the earth’s oceans. Other greenhouse gases are significantly affected by human activities. Burning fossil fuels and deforestation in the Tropics increase the amount of carbon dioxide in the atmosphere. Rice paddy farming and the digestive processes of livestock produce large amounts of methane. Fertilizers used in farming produce nitrous oxide, and refrigeration systems and some manufacturing processes release chlorofluorocarbons, other perfluorocarbons, and sulfur hexafluoride.
Since the mid-nineteenth century, carbon dioxide concentration in the air has increased from 280 parts per million to almost 380 parts per million. Normal carbon is carbon 12 (6 protons and 6 neutrons in the nucleus), but about 1 percent of carbon is carbon 13 (6 protons and 7 neutrons). Plants prefer carbon 12, so plant carbon (and fossil fuels from plants) has a smaller ratio of carbon 13 to carbon 12 than the atmosphere does. Analysis of air bubbles in ice cores shows that...
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Politics (Encyclopedia of Environmental Issues, Revised Edition)
Under the sponsorship of the United Nations, the Kyoto Protocol was adopted in December, 1997, and went into force in February, 2005. Seeing the protocol as flawed because it places no limits on China (the world’s largest polluter) or India, the United States opted out of the protocol. Under the protocol, industrialized nations set goals for greenhouse gas reductions, and developing nations negotiated for money from those nations to help them industrialize with fewer greenhouse emissions. By 2007 only Germany, Norway, France, and the United Kingdom were meeting their goals. Several nations that had been part of the former Soviet Union reduced emissions, in large part because their economies floundered.
In December, 2009, the U.S. Environmental Protection Agency (EPA) released a finding that greenhouse gases threaten the public health and welfare of the American people. The finding will allow the EPA to regulate greenhouse gas emissions in the United States if the Congress fails to pass legislation to do so.
In November, 2009, a large number of e-mails were stolen from the Climatic Research Unit at the University of East Anglia, United Kingdom. Some climate change skeptics alleged that the e-mails provided evidence that scientists had doctored data on global warming. Subsequent investigations found evidence of frustration on the part of the climate researchers and a lack of willingness among them to share raw data, but no...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Houghton, John. Global Warming: The Complete Briefing. New York: Cambridge University Press, 2009.
Singer, S. Fred, and Dennis T. Avery. Unstoppable Global Warming: Every 1,500 Years. Updated ed. Lanham, Md.: Rowman & Littlefield, 2008.
Weart, Spencer W. The Discovery of Global Warming. Rev. ed. Cambridge, Mass.: Harvard University Press, 2008.
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Background (Encyclopedia of Global Warming)
Greenhouse gases (GHGs) have both natural and anthropogenic sources. They allow sunlight to pass through them and reach Earth’s surface, but they trap the infrared radiation released by Earth’s surface, preventing it from escaping into space. These trace atmospheric gases thus play an important role in the regulation of Earth’s energy balance, raising the temperature of the lower atmosphere. GHG concentrations in the atmosphere have historically varied as a result of natural processes, such as volcanic activity. They have always been a small fraction of the overall atmosphere, however, exhibiting significant effects on the climate despite their low concentrations. Thus, small variations in GHG concentration may have disproportionate effects on Earth’s climate. Since the Industrial Revolution, humans have added a significant amount of GHGs to the atmosphere by burning fossil fuels and cutting down trees. Scientists estimate that the Earth’s average temperature has already increased by 0.3° to 0.6° Celsius since the beginning of the twentieth century.
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GHG Sources and Atmospheric Physics (Encyclopedia of Global Warming)
The atmosphere comprises constant components and variable components. It is composed primarily of nitrogen (78 percent) and oxygen (21 percent). Its other constant components include argon, neon, krypton, and helium. Its variable components include carbon dioxide (CO2), water vapor (H2O), methane (CH4), sulfur dioxide (SO2), ozone (O3), and nitrous oxide (N2O). The variable components affect the weather and climate because they absorb heat emitted by Earth and thereby warm the atmosphere. In addition to the variable natural atmospheric GHGs, anthropogenic halocarbons, other chlorine- and bromine-containing substances, sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons contribute to the greenhouse effect.
CO2, composed of two oxygen atoms and one carbon atom, is a colorless, odorless gas deriving from carbon burning in the presence of sufficient oxygen. It is released to the atmosphere by forest fires, fossil fuel combustion, volcanic eruptions, plant and animal decomposition, oceanic evaporation, and respiration. It is removed from the atmosphere by CO2 sinks, seawater absorption, and photosynthesis.
Methane is a colorless, odorless, nontoxic gas consisting of four hydrogen atoms and one carbon atom. It is a constituent of natural gas and fossil fuel. It is released into the atmosphere when organic matter decomposes in oxygen-deficient environments. Natural sources include wetlands,...
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Effect on Climate Change (Encyclopedia of Global Warming)
The Working Groups of the Intergovernmental Panel on Climate Change (IPCC) presented a synthesis report in 2007, providing an integrated view of climate change from multiple perspectives. The report observed an increase of global air and ocean temperatures, melting of snows, and rising sea levels. The report estimated the one-hundred-year linear trend of Earth’s average temperature between 1906 and 2005 at an increase of 0.74° Celsius, significantly greater than the trend from 1901 to 2000(0.6° Celsius). The increase of temperature contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns.
Global average sea level has risen between 1961 and 2001 at an average rate of 1.8 millimeters per year and between 1993 and 2008 at an average rate of 3.1 millimeters per year. The increase is due largely to melting glaciers and polar ice sheets. Satellite data between 1978 and 2008 show that average annual extent of Arctic sea ice shrank by an average of 2.7 percent per decade. The average summertime extent shrank far more, an average of 7.4 percent per decade.
Increases have been reported in the number and size of glacial lakes and the rate of change in some Arctic and Antarctic ecosystems. Runoff and earlier spring peak discharge in many glacier- and snow-fed rivers have also increased. These increases have in turn had effects on the thermal structure and water quality of...
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Context (Encyclopedia of Global Warming)
In response to global warming, changes are being implemented to reduce GHG emissions. The United NationsFramework Convention on Climate Change prepared the 1997 Kyoto Protocol. Under the protocol, thirty-six states, including highly industrialized countries and countries undergoing transitions to a market economy, entered into legally binding agreements to limit and reduce GHG emissions. Developing countries assumed nonbinding obligations to limit their emissions as well.
In the energy sector, fuel use is slowly transitioning from coal to natural gas and renewable energy (hydropower, solar, wind, geothermal, tidal, wave, and bioenergy). In the transport sector, fuel-efficient, hybrid, and fully electric vehicles are being designed and marketed, and governments are attempting to motivate commuters to use mass-transit systems. More efficient uses of energy, including low-energy lightbulbs, day lighting, and efficient electrical, heating, and cooling appliances are being developed and deployed.
Industrial manufacturers have implemented electrical efficiency measures as well, and they have begun recycling, as well as capturing and storing CO2. Crop and land management techniques have also improved, leading to an increase in soil carbon storage and the restoration of peaty soils and degraded land. Rice cultivation techniques have been improved, and livestock management techniques are being developed to reduce methane and nitrogen...
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Further Reading (Encyclopedia of Global Warming)
Dlugokencky, E. J., et al. “Continuing Decline in the Growth Rate of the Atmospheric Methane Burden.” Nature 393 (1998): 447-450. Presents analyses and measurements of methane in the atmosphere and shows a decreasing trend.
Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. Emmaus, Pa.: Rodale, 2006. Gore, the former vice president of the United States, presents documentary examples of global warming’s effects on Earth.
Le Treut, H., et al. “Historical Overview of Climate Change.” In Climate Change, 2007—The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by Susan Solomon et al. New York: Cambridge University Press, 2007. Contains an evaluation of climate change as an effect of the temperature increase at the Earth’s surface.
Walker, Gabrielle. An Ocean of Air: Why the Wind Blows and Other Mysteries of the Atmosphere. Orlando, Fla.: Harcourt, 2007. Informative book about air, processes in the atmosphere, and the climate.
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