Carbon Dioxide Equivalent (CDE)
Carbon Dioxide Equivalent (CDE)
A carbon dioxide equivalent (CDE, or CO2E) is the standard measure used to report greenhouse gas emissions. It provides a meaningful comparison of greenhouse gas emissions by providing a measure of the quantity of the gas emitted, while taking into account the relative effect of the gas on global warming compared to the effect of carbon dioxide.
Historical Background and Scientific Foundations
Greenhouse gases are gases that contribute to Earth's greenhouse effect by absorbing and emitting infrared radiation. Greenhouse gases directly affect Earth's atmosphere by absorbing and trapping infrared radiation, thereby contributing to global warming.
Greenhouse gases can also have an indirect effect on the atmosphere. This occurs when a greenhouse gas undergoes a chemical reaction to produce a second greenhouse gas, influences other greenhouse gases (for example, increasing their lifetime), or alters some other aspect of the atmosphere that affects radiation, such as promoting cloud formation.
Differences in the effect of each greenhouse gas means that the impact each gas has on the greenhouse effect cannot be measured only by reporting the quantity of each gas released. Instead, greenhouse gas emissions must be reported based on the impact the gas has on the greenhouse effect.
Impacts and Issues
Global warming potential (GWP) is the measure used to indicate the ability of a greenhouse gas to trap heat energy in the atmosphere. The GWP of a greenhouse gas is given as compared to carbon dioxide, which has a GWP of 1. The GWP can also be given over different time horizons. The Intergovernmental Panel on Climate Change (IPCC) has standardized the measurements for 20-year, 100-year, and 500-year GWPs for greenhouse gases.
The 100-year GWPs of methane, nitrous oxide, sulfur hexafluoride, and HFC-23 are 23, 296, 22,000, and 12,000 respectively. This indicates that each gram of methane has the same global warming effect as 23 grams of carbon dioxide, while each gram of HCF-23 emitted has the same global warming effect as 12000 grams of carbon dioxide.
WORDS TO KNOW
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.
INFRARED RADIATION: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat.
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE(IPCC): Panel of scientists established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 to assess the science, technology, and socioeconomic information needed to understand the risk of human-induced climate change.
Measures of greenhouse gas emissions are reported by multiplying the GWP of a greenhouse gas by the mass of the emissions of that gas. This measure is known as the carbon dioxide equivalent (CO2E) and allows the amount of each greenhouse gas to be compared based on its effect on global warming.
Houghton, J. T., et al. Climate Change 2001: The Scientific Basis. Cambridge: Cambridge University Press, 2001.
“Fourth Climate Action Report to the UN Framework Convention on Climate Change.” U.S. Department of State, 2007 < http://www.state.gov/g/oes/rls/rpts/car/> (accessed November 6, 2007).