28–36 times more harmful (methane GWP 28)

The 28-36 times more harmful figure quantifies the Global Warming Potential (GWP) of methane relative to carbon dioxide over a 100-year time horizon — meaning one tonne of methane emitted to atmosphere traps as much heat over the next century as 28-36 tonnes of CO2. The range reflects scientific updates: IPCC Fourth Assessment Report (AR4, 2007) reported 25; AR5 (2013) reported 28-34; AR6 (2021) reports 27-30 depending on whether climate-carbon feedbacks are included. Most Indian carbon accounting frameworks currently use the AR5 figure of 28 for legacy projects and AR6 for new ones.

The GWP definition involves three factors:

• Radiative efficiency: methane absorbs infrared radiation about 120 times more strongly per molecule than CO2.
• Atmospheric lifetime: methane persists about 12 years versus CO2's complex multi-century to multi-millennial removal profile.
• Time horizon: integrating heat trapping over 100 years dilutes methane's short-term punch; over 20 years, methane GWP rises to 80-87.

For waste-processing sectors in India, the 28-36x figure has profound economic and regulatory implications:

• CBG plant climate value: every tonne of organic waste diverted from open dumping or landfill prevents 50-150 kg of methane emissions (5-15 kg per tonne x 28-36 GWP), creating 1.4-5.4 tonnes CO2e of avoided emissions — monetisable under carbon markets at 600-2,500 INR per tonne CO2e.
• Fugitive methane leaks at CBG plants: are the dominant climate risk. A 2% methane slip during upgrading on a 10 TPD CBG plant emits about 80 kg methane per day = 2.4 tonnes CO2e daily, eroding the climate value the plant otherwise creates.
• Landfill gas capture: each tonne of methane captured and combusted (converting to CO2) reduces climate impact by a factor of 28-36; this is the foundation of landfill gas-to-energy carbon project methodologies.
• Global Methane Pledge (2021): India did not join the headline pledge but has aligned bilateral commitments to methane reductions in oil and gas, agriculture, and waste sectors.

Methane's short atmospheric lifetime creates a strategic trade-off in climate policy: reducing methane delivers fast climate benefit and helps meet 2030 targets, but does not resolve the long-term CO2 stabilisation problem. CO2 abatement remains essential because CO2 emissions accumulate for centuries. Most credible corporate net-zero strategies in India (including those aligned with SBTi) address both gases in parallel, treating methane reduction as a high-impact near-term lever and CO2 reduction as the long-term transformation.