Global Warming Potential (GWP)

Global Warming Potential (GWP) is the metric used to express the climate impact of different greenhouse gases relative to CO₂ over a defined time horizon — the conversion factor that makes CO₂e possible.

Global Warming Potential (GWP): The Conversion Factor Behind Every CO₂e Value

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Global Warming Potential (GWP) is the metric used to quantify and compare the climate impact of different greenhouse gases (GHGs) relative to carbon dioxide (CO₂) over a defined time period. It is the conversion factor that makes CO₂e (carbon dioxide equivalent) possible: by expressing each GHG's warming contribution as a multiple of CO₂'s warming contribution over the same time horizon, GWP allows methane, nitrous oxide, fluorinated gases, and dozens of other GHGs to be summed into a single, comparable carbon footprint figure.

Without GWP, there would be no meaningful way to compare the climate impact of, say, one kilogram of methane with one kilogram of CO₂ — or to aggregate them into a single Product Carbon Footprint (PCF) or Corporate Carbon Footprint (CCF).

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How GWP works

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GWP is calculated by comparing the total amount of energy a given mass of a GHG absorbs in the atmosphere over a specific time horizon to the energy absorbed by the same mass of CO₂ over the same period. CO₂ has a GWP of 1 by definition — all other gases are expressed relative to this baseline.

Key GHG GWP values (IPCC AR6, 100-year time horizon):

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According to the IPCC AR6, the 100-year Global Warming Potential (GWP100) varies significantly across greenhouse gases. While carbon dioxide (CO₂) serves as the baseline with a GWP of 1, methane (CH₄) has a GWP of 27.9, and nitrous oxide (N₂O) reaches 273.

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Fluorinated gases have even higher values. For example, HFC-134a (C₂H₂F₄), commonly used as a refrigerant, has a GWP of 1,526, while HFC-23 (CHF₃) reaches 14,600. Sulfur hexafluoride (SF₆), used in electrical insulation, has an exceptionally high GWP of 25,200.

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This means that one kilogram of methane has the same warming effect as 27.9 kilograms of CO₂ over 100 years — and is therefore counted as 27.9 kg CO₂e in a carbon footprint calculation using this GWP factor.

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For powerful fluorinated gases used in refrigeration or electrical equipment, these multipliers can reach into the thousands or tens of thousands, making even small leaks or losses highly significant for carbon accounting.

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GWP100: the standard time horizon

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The most widely used GWP time horizon is 100 years (GWP100) — the version required by the GHG Protocol, ISO 14067, and the vast majority of carbon reporting frameworks including CSRD and CBAM. GWP100 values are published by the Intergovernmental Panel on Climate Change (IPCC) in its Assessment Reports; the most current values come from IPCC AR6 (2021), which revised several GWP values upward compared to AR5.

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Other time horizons exist — GWP20 (which gives much higher weight to short-lived gases like methane because it looks at a shorter window) and GWP500 — but GWP100 is the standard for all major regulatory and voluntary reporting frameworks, and the version used in sustamize's CO₂e databases.

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GWP, CO₂e, and PCF calculations

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In a Product Carbon Footprint or Scope 3 calculation, GWP values are built into the emission factors in the database: each emission factor already expresses the result in CO₂e, having applied the relevant GWP100 values to convert all GHGs into a CO₂-equivalent basis. For most product carbon footprints, CO₂ itself is the dominant gas — but for products or processes involving refrigerants, certain fertilizers, or specific industrial processes, the non-CO₂ GHGs and their GWP values can represent a significant share of the total footprint.

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The choice of IPCC Assessment Report generation matters: switching from AR5 to AR6 GWP values changes the CO₂e result for methane-intensive processes and supply chains, and some regulatory frameworks are starting to specify which IPCC generation must be used. For ISO 14067-aligned PCFs, transparency about the GWP source (IPCC AR5 or AR6) is a disclosure requirement.

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Why GWP matters for procurement and supply chain decisions

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For procurement teams evaluating materials and suppliers, GWP-based CO₂e values are the common language that makes carbon comparison possible: whether comparing two steel suppliers, evaluating polymer alternatives, or assessing logistics routes, every comparison rests on CO₂e values derived from GWP100 emission factors. The quality of those emission factors — including whether they use current IPCC AR6 GWP values or outdated ones — directly affects the accuracy of the comparison.

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