Global Warming Potential

Global warming potential is the conversion factor that makes CO₂e possible. Without GWP values, emissions from methane, nitrous oxide, or F-gases could not be expressed as a single comparable figure. 

GWP values are published by the Intergovernmental Panel on Climate Change (IPCC) and updated periodically as scientific understanding improves. They are calculated based on the intensity of infrared absorption by each gas and how long emissions remain in the atmosphere.

The time period most commonly used for GWPs is 100 years, referred to as GWP-100. This is the standard applied in corporate carbon accounting and most reporting frameworks, including the GHG Protocol. A shorter 20-year horizon (GWP-20) is sometimes referenced, particularly for methane, but GWP-100 remains the convention for disclosure purposes.

In practice, GWP acts as a multiplier. A GWP value of 25 for a given gas means one tonne of gas has 25 times the warming impact of one tonne of CO₂. To calculate CO₂e, you multiply the mass of the emission by its GWP value. This allows organisations to aggregate emissions across different gases into a single inventory figure.

When building a carbon inventory, GWP values are a given, not a choice. They come from IPCC Assessment Reports, and the version applied should be recorded, as different frameworks and jurisdictions do not always reference the same one.