GWPs

Global Warming Potential (GWP) is a metric used to compare the climate impact of different greenhouse gases. It expresses the amount of heat a given mass of a gas traps in the atmosphere over a specified time horizon, relative to the same mass of carbon dioxide (CO2), which has a GWP of 1. GWPs are used to convert emissions of various gases into CO2-equivalents (CO2e) for reporting and policy analysis.

GWP depends on two factors: the gas’s radiative efficiency and its atmospheric lifetime. The calculation integrates the gas’s radiative forcing over the chosen horizon and divides by the same integral for CO2. Because gases persist for different lengths of time, a gas’s GWP can vary significantly between a 20-year horizon and a 100-year horizon, and even more for longer horizons.

Common values (as used in IPCC assessments) include: CO2 = 1 by definition. Methane (CH4) GWP100 is about 28–36, with a higher GWP20 of roughly 84–87. Nitrous oxide (N2O) GWP100 is around 265. Fluorinated gases can have very large GWPs; sulfur hexafluoride (SF6) is about 23,500 over 100 years. Other hydrofluorocarbons and perfluorocarbons span wide ranges depending on the gas and horizon.

Uses and limitations: GWPs are widely used in national inventories, climate pledges, and life cycle assessment to convert mix emissions into CO2e. They are simplifications and have limitations: a single number cannot capture all climate impacts, feedbacks, or damages, and results depend on the chosen time horizon. Some researchers explore alternative metrics or multiple horizons to address these issues.

History and context: GWPs were introduced by the IPCC in 1990 to enable cross-gas comparisons and are incorporated in frameworks such as the UNFCCC and the Kyoto Protocol. They remain standard in policy, though discussions continue about complementary metrics.