highglobalwarmingpotential

High global warming potential (high-GWP) refers to greenhouse gases with a large ability to trap heat in the Earth's atmosphere relative to carbon dioxide (CO2) over a specified time horizon. The GWP is a dimensionless index used in climate science and policy to compare the climate impact of emitting different gases.

GWP is calculated as the integrated radiative forcing per unit mass of a gas over a chosen time horizon, usually 100 years, divided by the same quantity for CO2. It depends on the gas's radiative efficiency and atmospheric lifetime. Because lifetimes and spectral properties differ, the ranking of gases can change with the chosen horizon; some gases have much higher GWP over 20 years than 100 years.

Examples illustrate the scale of high-GWP substances. CO2 has a GWP of 1 by definition. Methane has a GWP of about 28–36 over 100 years. Nitrous oxide is about 298. Among the highest are sulfur hexafluoride (SF6), with a GWP around 23,500 over 100 years, and many fluorinated gases (HFCs, PFCs, halons) with GWPs ranging from hundreds to tens of thousands.

Policy relevance is significant, as high-GWP gases are targeted for regulation and phasedown in many frameworks. The Kigali Amendment to the Montreal Protocol and other international agreements aim to reduce emissions of high-GWP refrigerants, solvents, and manufacturing by-products. GWP values also underpin national greenhouse gas inventories and aid in evaluating mitigation options.

Limitations include that GWP abstracts away certain dynamics, such as nonlinearity, indirect climate effects, and time-varying emission profiles. Some analyses use alternative metrics (for example, GWP) to address these limitations and provide a more nuanced view of long-term impacts.