Global Warming Potential (GWP)

Global Warming Potential (GWP) is a factor that quantifies the relative climate impact of a greenhouse gas compared with carbon dioxide (CO₂) over a given time horizon, normally 20 or 100 years. It is the metric that allows different gases to be added together and expressed in a single unit, the CO₂ equivalent (CO₂e).

The IPCC publishes updated values in its assessment reports. The current reference is the Sixth Assessment Report (AR6, 2021), whose 100-year values (GWP100) replace the older figures from AR4 and AR5.

How CO₂ equivalent is calculated

The total in CO₂e is obtained by multiplying the mass of each gas by its GWP and adding the results:

CO₂e = Σ (mass of gas × GWP of that gas)

Main IPCC AR6 GWP100 values

• CO₂ = 1 (reference).
• Fossil methane (CH₄) = 29.8.
• Non-fossil (biogenic) methane (CH₄) = 27.0.
• Nitrous oxide (N₂O) = 273.
• Sulphur hexafluoride (SF₆) = 25,200.
• HFC-134a = 1,530.

Fossil methane has a higher value than biogenic methane because, when it oxidises in the atmosphere, it adds CO₂ from fossil carbon that was not previously part of the natural carbon cycle. Over a 20-year horizon (GWP20) methane values are much higher (around 80 for fossil methane), which is why the time horizon used must always be stated.

Use in inventories, LCA and reporting

• ISO 14064-1 for corporate greenhouse gas inventories.
• ISO 14067 and Environmental Product Declarations (EPDs) for product carbon footprints.
• The GHG Protocol, which references the IPCC values and is undergoing a major revision begun in 2023.
• The EU Carbon Border Adjustment Mechanism (CBAM), whose definitive regime applies from January 2026 and relies on embedded-emissions calculations.

Good practice when updating inventories

• Always declare which IPCC report and GWP version you used (AR5 or AR6) so results stay comparable.
• Moving from AR5 to AR6 changes the CO₂e attributed to methane, so a recalculation can shift a footprint where methane is significant.
• Related but distinct metrics exist, such as GTP (Global Temperature change Potential) and GWP*, which better captures the short-lived behaviour of methane.

GWP is the cornerstone of climate accounting: using the most recent IPCC factors keeps your figures scientifically sound and aligned with frameworks such as CBAM and the CSRD. At Manglai we help companies measure their carbon footprint and prepare their sustainability reporting with up-to-date emission factors. Discover how Manglai can help you.