Carbon dioxide
Carbon dioxide
Environmental ChemistryIntroduction
Carbon dioxide (CO2) is the most important greenhouse gas produced by human activities, primarily through the combustion of fossil fuels. Its concentration in the Earth's atmosphere has risen by more than 30% since the Industrial Revolution. Charles D. Keeling was a pioneer in the monitoring of carbon dioxide concentrations in the atmosphere. Atmospheric mixing ratios for carbon dioxide are now higher than at any time in the last 800,000 years, standing at 380 parts per million (ppm) compared to a pre-industrial high of 280ppm. The current rate of increases is around 2ppm per year (see Figure 1).
Sources of Carbon dioxide
Figure 1: The following graph illustrates the rise in atmospheric carbon dioxide from 1744 to 2005. Note that the increase in carbon dioxide's concentration in the atmosphere has been exponential during the period examined. An extrapolation into the immediate future would suggest continued increases. (Source: PhysicalGeography.net)
Respiration
Respiration, both on land and in the sea, is a key component of the global carbon cycle. On land, an estimated 60 Pg C (60 billion tonnes) is emitted to the atmosphere each year by autotrophic respiration. A similar amount, about 55 Pg C, is emitted as a result of heterotrophic respiration.
In the sea, autotrophic respiration is thought to account for about 58 Pg of the dissolved inorganic carbon in surface waters each year, with the contribution of heterotrophic respiration being 34 Pg C.
Vulcanism
Emissions of CO2 due to volcanic activity, though sometimes large on a local scale, are relatively minor on a global scale, accounting for between 0.02 and 0.05 Pg C per year.
Land-use Change
It is estimated that man-made changes in land-use have, until now, produced a cumulative global loss of carbon from the land of about 200 Pg. Widespread deforestation has been the main source of this loss, estimated to be responsible for nearly 90 percent of losses since the mid-nineteenth century. Losses primarily occur due to the relatively long-term carbon sinks of forests being replaced by agricultural land.
The conversion of land from forested to agricultural land can have a wide range of negative effects as far as greenhouse gas emission is concerned. Soil disturbance and increased rates of decomposition in converted soils can both lead to emission of carbon to the atmosphere, with increased soil erosion and leaching of soil nutrients further reducing the potential for the area to act as a sink for carbon.
Current estimates suggest land-use changes lead to the emission of 1.7 Pg C per year in the tropics, mainly as a result of deforestation, and to a small amount of uptake (about 0.1 Pg C) in temperate and boreal areas - so producing a net source of around 1.6 Pg C per year.
Energy - Stationary Sources
Of the carbon dioxide emissions arising from fossil fuel combustion—up to 6.5 Pg C each year—around 40% is a result of electricity generation, with coal-fired generation being the leading sector. Other stationary sources include industrial (particularly iron and steel manufacture), emissions resulting from oil extraction, refinement and transportation, and domestic and commercial fossil fuel use.
Energy - Mobile Sources
Globally, transport-related emissions of carbon dioxide are growing rapidly. They currently consitute around 24% of anthropogenic CO2 emissions. Road transport dominates these emissions, though off-road, air and marine transport emissions are aslo significant. The use of petroleum as a fossil fuel for transportation dominates carbon dioxide emissions from this source. In 1999, in the U. S., more than 30 percent of fossil fuel-related carbon dioxide emissions were a direct result of transportation. With about two-thirds of this being from gasoline consumption by motor vehicles and the remainder coming from diesel and jet fuel use in lorries and aircraft, respectively.
Industry (non-energy-related)
Carbon dioxide is produced in lime and cement manufacture as a result of the heating of limestone. The final amount of CO2 produced varies depending the type of cement being made. Globally, this source is estimated to amount to 0.2 Pg C emission to the atmosphere each year. Significant carbon dioxide emissions (around 0.25 PgC per year) also result from its use in chemical feedstocks.
Biomass Burning
Though responsible for large CO2 emissions over short time-scales, the net CO2 emissions due to biomass burning are difficult to quantify due to the subsequent uptake of CO2 through regrowth of vegetation. An unsustainable (i.e., not off-set by regrowth) fraction equivalent to about 10% of total emissions is generally assumed biomass used in energy-generation, with this figure being incorporated into the total emissions resulting from land-use change.
Further Reading
- Climate Change 2001: The Scientific Basis. IPCC 2001. Full text.
- Carbon dioxide Capture and Storage. IPCC 2005 Full text.
- Greenhouse Gas Sinks. Reay etal. (eds). CABI Publishing (in press).
- PhysicalGeography.net
Citation
Dave Reay, Michael Pidwirny (Lead Author);Jay Gulledge, Sidney Draggan (Topic Editor) "Carbon dioxide". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth May 17, 2010; Last revised Date February 19, 2011; Retrieved February 6, 2012 <http://www.eoearth.org/article/Carbon_dioxide>
The Authors
Dave Reay was born in Hampshire, in 1972. He studied Marine Biology at Liverpool University and graduated in 1994. He went on to gain a Ph.D. at Essex University studying the response of Southern Ocean algae and bacteria to temperature change. After gaining his doctorate he continued working as a post-doc at Essex, investigating the impact of land-use on the soil methane sink. In 2001 he moved to Edinburgh University to investigate emissions of the greenhouse gas nitrous oxide from agriculture ... (Full Bio)
Michael Pidwirny studied Physical Geography at the University of Winnipeg and the University of Manitoba. He received his PhD from the Simon Fraser University in Burnaby, British Columbia in 1994. He currently is an Associate Professor of Physical Geography at the University of British Columbia, Okanagan Campus. Pidwirny’s research interests include climate change, the influence of land-use change on biodiversity, and the use of technology in education. He publishes regularly in encyclo ... (Full Bio)
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Comments
Posted by Milton Beychok on September 12, 2011 8:21 pm
The title of this article should be revised to reflect the fact that it is entirely about carbon dioxide as a greenhouse gas.
If the title is not changed, than readers should be provided at least some of the physical and chemical properties of the gaseous chemical compound named carbon dioxide. For example, the article should at least include the chemical compound's molecular weight, melting point, boiling point, color, odor, density, solubility in water, etc., etc.