What are greenhouse gases and CO2 equivalent (CO2e)?
Which gases warm the planet, how CO2 equivalent and global warming potential work, why reports use different GWP values, and where India's emissions come from.
What is global warming potential (GWP)?
The IPCC (AR6 Working Group III glossary, 2022) describes GWP as an index of how much heat a unit mass of a gas traps over a chosen time horizon, compared with the same mass of carbon dioxide. It combines two things: how strongly the gas absorbs heat and how long it stays in the air.
The time horizon changes the answer, especially for methane, which is powerful but short-lived:
| Gas | GWP over 20 years (AR6) | GWP over 100 years (AR6) |
|---|---|---|
| Methane, non-fossil | 79.7 | 27.0 |
| Methane, fossil | 82.5 | 29.8 |
| Nitrous oxide | 273 | 273 |
Source: IPCC AR6 Working Group I, Chapter 7, Table 7.15 (2021).
Fossil methane, from coal mines or gas leaks, has a slightly higher value because its carbon was not recently taken from the air, so the carbon dioxide it eventually turns into adds to warming. The GHG Protocol (August 2024) advises using the fossil value for leaks from fossil fuel systems and the non-fossil value for other sources, including fuel combustion.
The IPCC does not say that any one metric is correct; the right choice depends on the purpose. Most climate rules and company reporting use the 100-year GWP.
Sources: IPCC AR6 Working Group I, Summary for Policymakers (2021); IPCC AR6 Working Group I, Chapter 7: The Earth's Energy Budget, Climate Feedbacks and Climate Sensitivity (2021); IPCC AR6 Working Group III, Annex I: Glossary (2022); GHG Protocol, IPCC Global Warming Potential Values, Version 2.0 (August 2024); MoEFCC, India First Biennial Transparency Report (BTR-1) to the UNFCCC; MoEFCC, India Fourth Biennial Update Report (BUR-4), December 2024; UNFCCC Decision 18/CMA.1, Modalities, procedures and guidelines for the transparency framework; UNFCCC Decision 5/CMA.3, Guidance for operationalizing the modalities, procedures and guidelines for the enhanced transparency framework; Press Information Bureau / PM India: Cabinet approves ratification of Kigali Amendment to the Montreal Protocol (August 2021); 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 2, Chapter 1
This article was prepared with AI assistance and checked by the GreenEye team against the sources shown in each section.
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