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 are the common mistakes with CO2e?
- Mixing carbon and carbon dioxide. Some forestry and soil studies report tonnes of carbon (C), not CO2. One tonne of carbon equals about 3.67 tonnes of CO2, because the molecular weight ratio of CO2 to C is 44 to 12.
- Mixing GWP sets. Adding an AR5-based number to an AR6-based number gives a wrong total.
- Picking the time horizon that suits a story. A 20-year GWP makes methane look about three times bigger than the 100-year value. Both are valid for different questions, but the choice should be stated.
- Forgetting units. Check whether a number is in kg, tonnes or million tonnes, and whether it is CO2 only or CO2e.
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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