Which of the following gases is used as the reference for measuring the global…

Concept

Global warming potential compares the time-integrated radiative forcing caused by an equal mass emission of a gas with that caused by an equal mass emission of a reference gas over a selected time horizon.

The comparison combines radiative efficiency with atmospheric persistence, while the reference gas is assigned a GWP of 1.

Application

In the standard IPCC definition, carbon dioxide is the reference gas. Its GWP is therefore 1, and the GWP values of methane, chlorofluorocarbons, hydrofluorocarbons, and other greenhouse gases are expressed relative to it.

Contrast

• Methane is compared with the reference and has a different atmospheric lifetime and radiative efficiency.

• Chlorofluorocarbons are compared with the reference and can have very high GWP values because of strong radiative effects and long lifetimes.

• Hydrofluorocarbons are also compared with the reference; their GWP values vary by compound.

Cross-check

IPCC assessment tables list carbon dioxide with GWP = 1 and list the other gases with values relative to that baseline. Hence the required reference gas is carbon dioxide.