Global warming potential (GWP)
The factor that converts a greenhouse gas into an equivalent quantity of CO₂, over a given time horizon.
Different gases warm the planet by different amounts and persist for different lengths of time. GWP puts them on one scale so they can be added up as CO₂-equivalent.
The horizon matters. GWP100 — a hundred-year horizon — is the convention in most reporting. Methane looks far worse on a twenty-year horizon than on a hundred-year one, because it is potent but short-lived.
Values are revised as the science is updated: IPCC assessment reports have changed methane’s GWP100 more than once. So a CO₂e total is only comparable with another if both used the same assessment report.
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