Global Warming Potential (GWP) is a measure of how much heat a given greenhouse gas traps in the atmosphere over a specified time period (usually 100 years), expressed relative to carbon dioxide. CO₂ has, by definition, a GWP of 1.
GWP values are published by the Intergovernmental Panel on Climate Change (IPCC) and updated periodically. The current authoritative values come from the IPCC's Sixth Assessment Report (AR6); earlier UK reporting used AR4 and AR5.
Why it matters
GWP is what allows different greenhouse gases to be combined into a single tCO₂e figure. Without it, you could not meaningfully add a tonne of methane to a tonne of CO₂ — they have very different warming impacts.
It matters most for refrigerant emissions (Scope 1 fugitive emissions), where modern HFC refrigerants can have GWPs in the thousands. A small kilogramme-scale leak of a high-GWP refrigerant can produce more tCO₂e than several tonnes of CO₂ from fuel combustion.
A practical example
Methane has a 100-year GWP of roughly 28 (per IPCC AR6). A 1-tonne leak of methane is therefore equivalent to 28 tCO₂e. Refrigerant R410A has a GWP of roughly 2,088 — a 1 kg leak is equivalent to about 2.1 tCO₂e.
We use GWP values from the latest IPCC report, as published in the DEECC conversion factors. See where they apply on the methodology page.