Which gas is used as a reference for measuring GWP?

• A. Methane
• B. Carbon Dioxide
• C. Nitrous Oxide
• D. Water Vapor

Answer: (B)

Global Warming Potential is a way to compare how much heat a given amount of a greenhouse gas traps in the atmosphere relative to carbon dioxide over a chosen time horizon. Carbon dioxide is used as the reference gas with a GWP of 1 because it’s long-lived, well-mixed, and its warming effect is well understood, making it a stable baseline for comparisons. When we say a gas has a GWP of X, we mean that one unit of that gas traps as much heat over the horizon as X units of CO2. The time horizon matters; over 100 years, methane is more potent per molecule than CO2 (about 28–34 times as warming), and nitrous oxide is around 300 times as warming. Water vapor isn’t assigned a GWP because it fluctuates rapidly with temperature and acts mainly as a feedback rather than a directly emitted long-lived gas, so it isn’t used as the reference.