Carbon dioxide equivalent
Encyclopedia
Carbon dioxide equivalent (CDE) and Equivalent carbon dioxide (or ) are two related but distinct measures for describing how much global warming
a given type and amount of greenhouse gas
may cause, using the functionally equivalent amount or concentration of carbon dioxide
as the reference.
that describes, for a given mixture and amount of greenhouse gas, the amount of that would have the same global warming potential
(GWP), when measured over a specified timescale (generally, 100 years). Carbon dioxide equivalency thus reflects the time-integrated radiative forcing of a quantity of emissions or rate of greenhouse gas emission—a flow into the atmosphere—rather than the instantaneous value of the radiative forcing of the stock (concentration) of greenhouse gases in the atmosphere described by e.
The carbon dioxide equivalency for a gas is obtained by multiplying the mass and the GWP of the gas. The following units
are commonly used:
For example, the GWP for methane over 100 years is 25 and for nitrous oxide 298. This means that emissions of 1 million metric tonnes of methane and nitrous oxide respectively is equivalent to emissions of 25 and 298 million metric tonnes of carbon dioxide.
as a given type and concentration of greenhouse gas. Examples of such greenhouse gases are methane
, perfluorocarbons, and nitrous oxide
. e is expressed as parts per million by volume
, ppmv.
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
a given type and amount of greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
may cause, using the functionally equivalent amount or concentration of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
as the reference.
Global warming potential
Carbon dioxide equivalency is a quantityQuantity
Quantity is a property that can exist as a magnitude or multitude. Quantities can be compared in terms of "more" or "less" or "equal", or by assigning a numerical value in terms of a unit of measurement. Quantity is among the basic classes of things along with quality, substance, change, and relation...
that describes, for a given mixture and amount of greenhouse gas, the amount of that would have the same global warming potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...
(GWP), when measured over a specified timescale (generally, 100 years). Carbon dioxide equivalency thus reflects the time-integrated radiative forcing of a quantity of emissions or rate of greenhouse gas emission—a flow into the atmosphere—rather than the instantaneous value of the radiative forcing of the stock (concentration) of greenhouse gases in the atmosphere described by e.
The carbon dioxide equivalency for a gas is obtained by multiplying the mass and the GWP of the gas. The following units
Units of measurement
A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...
are commonly used:
- By the UN climate change panel IPCCIntergovernmental Panel on Climate ChangeThe Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
: billion metric tonnes of CO2 equivalent (GtCO2eq). - In industry: million metric tonnes of carbon dioxide equivalents (MMTCDE).
- For vehicles: g of carbon dioxide equivalents / km (gCDE/km).
For example, the GWP for methane over 100 years is 25 and for nitrous oxide 298. This means that emissions of 1 million metric tonnes of methane and nitrous oxide respectively is equivalent to emissions of 25 and 298 million metric tonnes of carbon dioxide.
Equivalent carbon dioxide
Equivalent (e) is the concentration of that would cause the same level of radiative forcingRadiative forcing
In climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...
as a given type and concentration of greenhouse gas. Examples of such greenhouse gases are methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
, perfluorocarbons, and nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
. e is expressed as parts per million by volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
, ppmv.
- e calculation example:
- The radiative forcing for pure is approximated by
where C is the present concentration, 
is a constant, 5.35 and 
the pre-industrial concentration, 278 ppm. Hence the value of e for an arbitrary gas mixture with a known radiative forcing is given by 
in ppmv. - To calculate the radiative forcing for a 1998 gas mixture, IPCCIntergovernmental Panel on Climate ChangeThe Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
2001 gives the radiative forcing (relative to 1750) of various gases as: =1.46 (corresponding to a concentration of 365 ppmv), CH4=0.48, N2O=0.15 and other minor gases =0.01 W/m2. The sum of these is 2.10 W/m2. Inserting this to the above formula, we obtain e = 412 ppmv.
- The radiative forcing for pure is approximated by
See also
- Carbon accountingCarbon accountingCarbon accounting is the accounting process undertaken to measure the amount of carbon dioxide equivalents that will not be released into the atmosphere as a result of Flexible Mechanisms projects under the Kyoto Protocol. These projects thus include renewable energy projects and biomass, forage...
- Emission standardEmission standardEmission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...
- Global warming potentialGlobal warming potentialGlobal-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...