Environmental Indicators

 Compiled by Rolando Delgado Castillo and Rafaela Perez Marchena


    Versión en Español                                                                         English version



Global Warming Potential: a number that refers to the amount of global warming caused by a substance


The GWP is the ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. Thus, the GWP of CO2 is defined to be 1.0 . CFC-12 has a GWP of 8,500, while CFC-11 has a GWP of 5,000. Various HCFCs and HFCs have GWPs ranging from 93 to 12,100. 

Source: US EPA Ozone Depletion Glossary


On its own however, GWP cannot describe the climate impact of a Greenhouse Gas.


The GWP (Global Warming Potential) is an index, specific to each gas, which expresses its climatic warming potential relative to that of carbon dioxide, which by convention is set at 1. It enables to compare the impacts of emissions and reductions of different greenhouse gases. According to the IPCC, GWPs typically have an uncertainty of ±35 percent.

The GWP is actually calculated in terms of the 100 year warming potential of a kilogram (kg) of a gas relative to that of a kilogram of CO2.

Because the decay of CO2 in the atmosphere follows a different pathway than the other Greenhouse Gases, the lifetime plays a role in the GWP values. The parties to the UNFCCC have also agreed to use GWPs based upon a 100 year time horizon.


Lifetime of greenhouse gases in the atmosphere

The longer a greenhouse gas stays in the atmosphere, the more its cumulative heating effect. Although the GWPS are calculated on a 100 years basis, lifetime becomes an important parameter for the longer term.

Actually, CO2 has a very long lifetime: it remains in the atmosphere for several thousand years and after 100 years has developed less than one quarter of its impact.

In contrast, HFCs are quickly removed from the atmosphere due to their relatively short atmospheric lifetimes, and their lifetimes are decades or less.

Unlike HFCs, which are removed from the atmosphere relatively quickly, the long lifetime of CO2 means a significant commitment for climate change long into the future. Compared to CO2.


Climate impact

The GWP has to be put into perspective. The total quantity released is as important as the GWP in calculating the real environmental impact.


Clearly GWP as a measure does not satisfactorily describe the climate impact of a greenhouse gas.

Despite the low GWP of CO2, the enormous quantities emitted and its long lifetime means that it has a far greater impact on climate than HFCs. Currently, CO2 emissions contribute 64% of the total greenhouse gas emissions and are rising.

Source: European Fluorocarbons Technical Committee (EFCTC)


Global Warming Potentials (GWPs) as a quantified measure of the globally averaged relative radiative forcing impacts


Global Warming Potentials (GWPs) are intended as a quantified measure of the globally averaged relative radiative forcing impacts of a particular greenhouse gas. It is defined as the cumulative radiative forcing -both direct and indirect effects - integrated over a period of time from the emission of a unit mass of gas relative to some reference gas (IPCC 1996). Carbon dioxide (CO2) was chosen as this reference gas. Direct effects occur when the gas itself is a greenhouse gas. Indirect radiative forcing occurs when chemical transformations involving the original gas produce a gas or gases that are greenhouse gases, or when a gas influences other radiatively important processes such as the atmospheric lifetimes of other gases. The relationship between gigagrams and Tg CO2 Eq. can be expressed as follows:

Tg CO2 Eq = (Gg of gas) x (GWP) x {Tg/ 1000 Gg}

where: Tg CO2 Eq = Teragrams of CO2 Equivalents; Gg = Gigagrams (equivalent to 1000 metric tons);

GWP = Global Warming Potential; Tg = Teragrams   


Source: U.S. Greenhouse Gas Inventory Program, Office of Atmospheric Programs, U.S Environmental Protection Agency, April 2002. 



Used to compare the abilities of different greenhouse gases

Global warming potentials (GWPs) are used to compare the abilities of different greenhouse gases to trap heat in the atmosphere. GWPs are based on the radiative efficiency (heat-absorbing ability) of each gas relative to that of carbon dioxide (CO2), as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of CO2. The GWP provides a construct for converting emissions of various gases into a common measure, which allows climate analysts to aggregate the radiative impacts of various greenhouse gases into a uniform measure denominated in carbon or carbon dioxide equivalents.

The generally accepted authority on GWPs is the Intergovernmental Panel on Climate Change (IPCC). In 2001, the IPCC updated its estimates of GWPs for key greenhouse gases.

Reference: IPCC Global Warming Potential page


Water Hazard Classification


The most important fluorocarbons have been classified for their impact on aquatic environment in Water Hazard Classes. The classification is committed according to the German “Administrative Regulation on the Classification of Substances Hazardous to Waters into Water Hazard Classes” (Verwaltungsvorschrift wassergefährdende Stoffe – VwVwS).

Three Water Hazard Classes (WGK) are defined:

  1. low hazard to waters
  2. hazard to waters
  3. severe hazard to waters

Source: European Fluorocarbons Technical Committee (EFCTC)

Ozone Depletion Potential (ODP): a number that refers to the amount of ozone depletion caused by a substance

The ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11. Thus, the ODP of CFC-11 is defined to be 1.0. Other CFCs and HCFCs have ODPs that range from 0.01 to 1.0. The halons have ODPs ranging up to 10. Carbon tetrachloride has an ODP of 1.2, and methyl chloroform's ODP is 0.11. HFCs have zero ODP because they do not contain chlorine.

Ozone-Depleting Substance(s) (ODS): a compound that contributes to stratospheric ozone depletion

ODS include CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone.

Chlorofluorocarbon (CFC): a compound consisting of chlorine, fluorine, and carbon

CFCs are very stable in the troposphere. They move to the Stratosphere and are broken down by strong ultraviolet light, where they release chlorine atoms that then deplete the ozone layer. CFCs are commonly used as refrigerants, solvents, and foam blowing agents.

The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115. The ozone depletion potential (ODP) for each CFC is, respectively, 1, 1, 0.8, 1, and 0.6.

Hydrochlorofluorocarbon (HCFC): a compound consisting of hydrogen, chlorine, fluorine, and carbon

The HCFCs are one class of chemicals being used to replace the CFCs. They contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs. HCFCs have ozone depletion potentials (ODPs) ranging from 0.01 to 0.1. Production of HCFCs with the highest ODPs will be phased out first, followed by other HCFCs. 

Hydrofluorocarbon (HFC): a compound consisting of hydrogen, fluorine, and carbon

The HFCs are a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. All HFCs have an ozone depletion potential of 0. Some HFCs have high GWPs.  .

Halon: a compound consisting of bromine, fluorine, and carbon

The halons are used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers. They cause ozone depletion because they contain bromine. Bromine is many times more effective at destroying ozone than chlorine. At the time the current U.S. tax code was adopted, the ozone depletion potentials of halon 1301 and halon 1211 were observed to be 10 and 3, respectively. These values are used for tax calculations. Recent scientific studies, however, indicate that the ODPs are at least 12 and 6, respectively. Note: technically, all compounds containing carbon and fluorine and/or chlorine are halons, but in the context of the Clean Air Act, "halon" means a fire extinguishing agent as described above. 

Hydrobromofluorocarbon (HBFC): a compound consisting of hydrogen, bromine, fluorine, and carbon

Hydrocarbon (HC): a compound consisting of carbon and hydrogen

Hydrocarbons include methane, ethane, propane, cyclopropane, butane, and cyclopentane. Although they are highly flammable, HCs may offer advantages as ODS substitutes because they are inexpensive to produce and they have zero ozone depletion potential, very low global warming potential (GWP), and low toxicity. 

Source: US EPA Ozone Depletion Glossary