Carbon Dioxide (CO2)

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Carbon Dioxide (CO2)

Introduction

Carbon dioxide consists of one carbon (C) atom doubly bonded to two oxygen (O) atoms to produce the molecular compound O=C=O, with the chemical symbol CO₂. It does not have color or odor, but carbon dioxide does have a slight sour taste. This acidic flavor is found in carbonated beverages because carbon dioxide gives such liquids their fizz. Under normal temperatures and pressures found on Earth, carbon dioxide is a gas but can also be found in liquid and solid states.

Scientists have learned that carbon dioxide is found in Earth's atmosphere in a proportion of about 300 to 400 parts per million (ppm). However, as the global climate has been studied, an increase in the concentration of carbon dioxide has been noticed by scientists at a rate of about 0.4% annually. This increase in concentration is important to the study of climate change because scientists contend that a portion of this increase is due to the combustion of fossil fuels and vegetation such as wood, petroleum, and coal.

Historical Background and Scientific Foundations

Flemish chemist Johannes van Helmont (1580-1644) observed that the final mass was less than the initial mass when charcoal burned in a closed container. Van Helmont

conjectured the difference was the removal of an invisible substance (eventually identified as carbon dioxide).

Later, Scottish chemist Joseph Black (1728–1799) produced an unknown substance—called “fixed air”— when he broke down chalk and limestone. Black is generally considered the first scientist to discover carbon dioxide.

WORDS TO KNOW

BIOSPHERE: The sum total of all life-forms on Earth and the interaction among those life-forms.

CARBON CYCLE: All parts (reservoirs) and fluxes of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest pool of carbon near the surface of Earth, but most of that pool is not involved with rapid exchange with the atmosphere.

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 GAS: A gaseous component of the atmosphere contributing to the greenhouse effect. Greenhouse gases are transparent to certain wavelengths of the sun's radiant energy, allowing them to penetrate deep into the atmosphere or all the way into Earth's surface. Greenhouse gases and clouds prevent some infrared radiation from escaping, trapping the heat near Earth's surface where it warms the lower atmosphere. Alteration of this natural barrier of atmospheric gases can raise or lower the mean global temperature of Earth.

INDUSTRIAL REVOLUTION: The period, beginning about the middle of the eighteenth century, during which humans began to use steam engines as a major source of power.

PHOTOSYNTHESIS: The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process, oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.

RESPIRATION: The process by which animals use up stored foods (by combustion with oxygen) to produce energy.

In addition, Swedish chemist Svante Arrhenius (1859–1927) was the first scientist to publish a paper about carbon dioxide emissions from the burning of fossil fuels. Arrhenius published “On the influence of carbonic acid in the air upon the temperature of the ground” in 1896.

Impacts and Issues

Carbon dioxide plays an important role in the carbon cycle, which involves an exchange of carbon dioxide between the biosphere (living beings), geosphere (land masses), hydrosphere (water bodies), and atmosphere (air).

Under photosynthesis, green plants convert carbon dioxide and water into food such as oxygen and glucose. Conversely, plants and animals release carbon dioxide in a process called respiration.

However, humans affect the amount of carbon dioxide released into the atmosphere with their artificially produced activities such as the burning of fossil fuels, clearing of forests, and the use of fuel-powered vehicles. Because of such activity, the concentration of carbon dioxide in the atmosphere has been steadily increasing since about 1850, the start of the second Industrial Revolution. As reported by the United Nations' Intergovernmental Panel on Climate Change (IPCC), between 1970 and 2004 the increase in CO₂ emissions has grown by about 80%.

IN CONTEXT: CO₂ CAPTURE AND STORAGE

“CCS [CO₂ Capture and Storage] in underground geological formations is a new technology with the potential to make an important contribution to mitigation by 2030. Technical, economic and regulatory developments will affect the actual contribution.”

SOURCE:Metz, B., et al.“IPCC, 2007: Summary for Policymakers.” In: 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.

The environmental problem called global warming is a worry to humans because of the noticed increase of greenhouse gases such as carbon dioxide. Scientists are investigating this greenhouse effect to see if the melting of glaciers and icebergs, increased storm activity, and warmer-than-normal temperatures are due to an exaggerated greenhouse effect. By 2050, the IPCC predicts that carbon dioxide in the atmosphere could reach 450 to 550 ppm.

BIBLIOGRAPHY

Books

Gunter, Valerie Jan. Volatile Places: A Sociology of Communities and Environmental Controversies. Thousand Oaks, CA: Pine Forge Press, 2007.

Mackenzie, Fred T. Carbon in the Geobiosphere: Earth's Outer Shell. Dordrecht, Netherlands: Springer, 2006.

National Academy of Engineering, National Research Council of the National Academies. The Carbon Dioxide Dilemma: Promising Technologies and Policies. Washington, DC: National Academies Press, 2003.

Web Sites

“Contributions of Working Group III to the Fourth Assessment Report of the Intergovermental Panel on Climate Change.” Intergovermental Panel on Climate Change, May 4, 2007. < http://www.ipcc.h/SPM040507.pdf> (accessed November 5, 2007).

Climate Change: In Context