Among the following greenhouse gases (GHGs), whose Global Warming Potential…

Concept

Global Warming Potential (GWP) compares the time-integrated radiative forcing caused by a unit mass of a greenhouse gas with that caused by the same mass of a reference gas over a specified time horizon.

The comparison gas defines the scale: its ratio to itself is the normalization point, while every other gas is measured relative to it.

Application

Carbon dioxide is the reference gas used for the GWP scale.

Contrast

• Chlorofluorocarbons are a family of compounds; their species-specific radiative efficiencies and atmospheric lifetimes produce GWPs well above the reference value.

• Nitrous oxide has strong radiative efficiency and a long atmospheric lifetime, so its GWP is substantially above the reference value.

• Methane has a shorter atmospheric lifetime than nitrous oxide but stronger warming per unit mass than the reference gas over standard assessment horizons.

Cross-check

Using GWPi = integrated forcing of gas i ÷ integrated forcing of the reference gas, substituting the reference gas for i makes numerator and denominator identical; the ratio is 1.

Result

The greenhouse gas whose GWP is considered 1 is carbon dioxide (CO2).