Carbon Dioxide

Carbon Dioxide

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Carbon dioxide (CO2) is a nontoxic, odorless, and colorless gas present in trace concentrations in the atmosphere. The molecule is linear with a central carbon atom doubly bonded to two oxygen atoms (O=C=O). Natural sources of CO2 include volcanic outgassing, animal respiration, biomass decay, and oceanic evaporation. Removal processes include photosynthesis and dissolution into the oceans .

CO2 is a long-lived gas, with an atmospheric lifetime of more than one hundred years. It is a natural greenhouse gas and plays an important role in regulating Earth's climate. Like water vapor, CO2 traps outgoing infrared radiation emitted by Earth into space. By absorbing this energy, the atmosphere warms the earth, a process known as the natural greenhouse effect. Without carbon dioxide and water in the atmosphere, the earth's average surface temperature would be below 0°F, turning oceans into ice and dramatically altering life as it is known.

CO2 is also an anthropogenic greenhouse gas, ranked number one for its contributions to global warming. At the beginning of the Industrial Era (around 1750), CO2 concentrations worldwide were approximately 280 parts per million (ppm); by 1999 concentrations reached 367 ppm. (One ppm equals one molecule of CO2 for every million molecules of air, or 0.0001 percent.) CO2 emissions continue to rise; the average rate of increase since 1980 is 0.4 percent per year.

The recent rise in anthropogenic CO2 is attributed largely to fossil fuel combustion (73 percent) and land use conversion resulting from deforestation (25 percent). When oil, coal, or natural gas is burned to generate energy, the by-products are CO2 and water. Due to heavy fossil fuel consumption, the United States leads the world in anthropogenic CO2 emissions (see table). In 1996 the United States contributed more than 50 percent of the 1.027 × 1016 grams of total global CO2 emissions.

As concentrations of CO2 increase in the atmosphere, more outgoing infrared energy is trapped (energy that would have escaped to space), warming the earth's atmosphere and surface. The Intergovernmental Panel on Climate Change estimates that the global surface temperature has increased by 1.1°F since the late nineteenth century, due to increases in CO2 and other greenhouse gases.

International efforts are underway to reduce CO2 and other greenhouse gases. As of December 2001, 186 countries ratified the Kyoto Protocol, an international agreement to reduce CO2 and other greenhouse gas emissions. CO2 emissions can be reduced by reforestation and afforestation efforts by changing cropland management practices such as tilling, and by reducing the combustion of fossil fuels. The United States did not sign the protocol, but promotes voluntary development of climate-friendly technologies (i.e., renewable energy sources) coupled with changes in land use and forestry practices. Examples of the latter include decreased deforestation, increased reforestation, and agricultural practices designed to increase soil carbon.

see also Electric Power; Emissions Trading; Global Warming; Greenhouse Gases; Petroleum; Vehicular Pollution.

Bibliography

Turco, Richard P. (1997). Earth under Siege: From Air Pollution to Global Change. New York: Oxford University Press.

Internet Resources

Intergovernmental Panel on Climate Change, Working Group I. "The Carbon Cycle and Atmospheric Carbon Dioxide." In Climate Change 2001: The Scientific Basis. Available from http://www.ipcc.ch.

United Nations Framework Convention on Climate Change. "Texts of the Convention and the Kyoto Protocol." Available from http://unfccc.int/resource.

United Nations Framework Convention on Climate Change, Conference of the Parties. Fourth session, Buenos Aires, November 2–13, 1998, Information 9. "Summary Compilation of Annual Greenhouse Gas Emissions Inventory Data from Annex I Parties." Available from FCCC/COP/1998/INF.9.

Marin Sands Robinson