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.
Why do different reports use different GWP values?
The IPCC updates GWP values in each assessment report as the science improves. Different rules point to different editions, so the same tonne of methane can show up as a different CO2e number.
| Edition | Methane | Nitrous oxide | Who uses it |
|---|---|---|---|
| Second Assessment Report (AR2, 1995) | 21 | 310 | India's Fourth Biennial Update Report (BUR-4, December 2024) for the 2020 inventory |
| Fifth Assessment Report (AR5, 2013-14) | 28 (non-fossil), 30 (fossil) | 265 | Reporting under the Paris Agreement transparency rules (UNFCCC decisions 18/CMA.1 and 5/CMA.3), including India's BTR-1 |
| Sixth Assessment Report (AR6, 2021) | 27.0 (non-fossil), 29.8 (fossil) | 273 | Recommended by the GHG Protocol (August 2024) for company reporting |
Under the Paris Agreement rules, countries report with the AR5 100-year values (decision 18/CMA.1, annex, paragraph 37; decision 5/CMA.3 specifies the AR5 table and excludes the fossil methane value). This is why India's BUR-4 and BTR-1 are not directly comparable without converting: BUR-4 multiplied methane by 21, while BTR-1 multiplied it by 28.
The lesson is simple: always check which GWP set a number uses before comparing it with another.
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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