Global Warming Potential (GWP) — a practical guide.
GWP is the unit that lets us compare the climate impact of different greenhouse gases on a single scale. This guide explains what it is, how it's calculated, and the values most often used in carbon inventories.
What is GWP?
Global Warming Potential measures how much energy the emissions of 1 tonne of a gas will absorb over a given time period, relative to the emissions of 1 tonne of carbon dioxide. The most commonly used time horizon is 100 years (GWP₁₀₀).
Reporting frameworks — including the GHG Protocol, ISO 14064 and Australia's NGER scheme — use GWP values to convert emissions of all greenhouse gases into a single "carbon dioxide equivalent" (CO₂e) figure.
How GWP is calculated
GWP combines two factors: the radiative efficiency of a gas (how strongly it traps heat per molecule) and its atmospheric lifetime (how long it persists before breaking down). Methane, for example, is far more potent than CO₂ per molecule but lifts out of the atmosphere within a decade or two — which is why its GWP₂₀ value is much higher than its GWP₁₀₀ value.
Common GWP₁₀₀ values (IPCC AR6)
| Gas | Formula | GWP₁₀₀ | Notes |
|---|---|---|---|
| Carbon dioxide | CO₂ | 1 | The reference gas — every other GWP is expressed relative to CO₂. |
| Methane (fossil) | CH₄ | 29.8 | Short-lived but very potent over a 20-year horizon (GWP₂₀ ≈ 82.5). |
| Nitrous oxide | N₂O | 273 | Long-lived; significant from agriculture and combustion. |
| HFC-134a | CH₂FCF₃ | 1,530 | Common refrigerant; being phased down under the Kigali Amendment. |
| Sulphur hexafluoride | SF₆ | 25,200 | Used in electrical switchgear; one of the most potent GHGs known. |
Source: IPCC Sixth Assessment Report (AR6), Working Group I, Chapter 7.
Why GWP matters for your inventory
GWP values determine how non-CO₂ emissions show up in your inventory totals. Choosing the right vintage (AR5 vs AR6) and the right time horizon (20 vs 100 years) can materially shift methane- and refrigerant- heavy footprints. Disclosure frameworks usually specify which vintage to use — confirm before you report.