GHGs: CO2, Methane, Nitrous Oxide

GHGs: CO2, Methane, Nitrous Oxide

GHGs: Scientific Basis & Classification

The Intergovernmental Panel on Climate Change (IPCC) defines greenhouse gases as “gases that absorb and emit infrared radiation, thereby trapping heat in the atmosphere” (IPCC AR6 WGIII, 2021, p. 5). Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) are the three long‑lived gases that dominate anthropogenic radiative forcing (IPCC AR6, 2021, Table 7.1). CO₂ concentration reached 416 ppm, CH₄ 1900 ppb, and N₂O 332 ppb in 2023 (NOAA Global Monitoring Laboratory, 2023). Their 100‑year global warming potentials are 1 for CO₂, 28 for CH₄, and 265 for N₂O (IPCC AR6, 2021, Annex B). Under the United Nations Framework Convention on Climate Change (UNFCCC) Annex I, these gases are listed as “greenhouse gases” for reporting and mitigation (UNFCCC, 1992, Annex I). The World Meteorological Organization (WMO) classifies them as long‑lived climate forcers because atmospheric lifetimes exceed a decade (WMO, 2022, Technical Note). They differ from short‑lived pollutants such as tropospheric ozone, which, despite warming the climate, are excluded from the UNFCCC greenhouse‑gas inventory. A common misconception is that any gas with a high GWP is a greenhouse gas; water vapour, for example, has a GWP orders of magnitude larger than CO₂ but is excluded because its concentration is temperature‑controlled rather than emission‑controlled. Likewise, CO₂ is not a toxic pollutant; its climate relevance derives from radiative forcing, not acute health effects. The scientific basis for treating CO₂, CH₄ and N₂O as distinct climate forcers rests on their spectroscopic absorption bands, atmospheric lifetimes, and anthropogenic emission trends documented in the IPCC Emissions Database (2022). Consequently, national inventories such as India’s National GHG Inventory 2022 report emissions of these three gases separately to align with IPCC methodology (MoEFCC, 2023).

💡 Key Insight: N₂O’s 100‑year GWP of 265 means it traps 265 times more heat per molecule than CO₂ over a century, despite being present at only ~332 ppb.

💡 Key Insight: Water vapour, while possessing a vastly larger GWP than CO₂, is omitted from UNFCCC inventories because its atmospheric concentration is driven by temperature, not direct emissions.

[!infographic: "Global atmospheric concentrations of CO₂, CH₄, and N₂O from 2000 to 2023, showing the steep rise in CO₂ and steady increases in CH₄ and N₂O"]<

[!infographic: "Spectroscopic absorption bands of CO₂, CH₄, and N₂O in the infrared region"]<

⚖️ Comparative Analysis: CO₂, CH₄, N₂O

GHG Emissions Governance Framework

The constitutional anchor for GHG governance lies in Article 48A (State duty to protect the environment) and Article 51A(g) (citizen duty to protect the environment) of the Constitution of India (1950). These provisions empower the Union and States to enact climate‑relevant statutes under the legislative competence defined in Article 246.

The Environment Protection Act 1986 (EPA 1986) establishes a comprehensive regulatory regime for all pollutants, delegating authority to the Ministry of Environment, Forest and Climate Change (MoEFCC) to issue emission standards for CO₂, CH₄ and N₂O. The Air (Prevention and Control of Pollution) Act 1981 (APC 1981) mandates continuous ambient‑air monitoring; the Central Pollution Control Board (CPCB) publishes annual PM₂.₅ and GHG inventories (CPCB, 2023).

Carbon sequestration is governed by the Forest Conservation Act 1980 (FCA 1980) and the Forest Rights Act 2006 (FRA 2006). FCA 1980 requires prior approval for any forest‑land conversion that would release stored CO₂, while FRA 2006 recognises community rights to forest carbon benefits, enabling joint‑implementation projects under the UNFCCC.

Energy‑related emissions are regulated by the Energy Conservation Act 2001 (ECA 2001) and its 2022 amendment, which introduced the Perform, Achieve and Trade (PAT) Scheme 2012 and the Carbon Trading Scheme 2022. PAT 2012 sets sector‑specific CO₂ intensity targets for energy‑intensive industries; the Carbon Trading Scheme 2022 creates a national registry for verified emission reductions, overseen by the Ministry of New and Renewable Energy (MNRE).

The National Action Plan on Climate Change 2008 (NAPCC 2008) delineates eight national missions, of which the National Mission for Sustainable Forest Management (NMSFM 2008) and the National Mission for Enhanced Energy Efficiency (NMEEE 2008) directly address CO₂ and CH₄ mitigation. The National Adaptation Fund for Climate Change 2015 (NAFCC 2015) finances adaptation projects that curtail N₂O emissions from agriculture.

International obligations are codified in the United Nations Framework Convention on Climate Change 1992 (UNFCCC 1992), the Kyoto Protocol 1997 (ratified 2002) and the Paris Agreement 2015 (ratified 2016). India’s Nationally Determined Contribution (NDC) submitted to the UNFCCC (2021) commits to a 33–35 % reduction in emissions intensity of GDP by 2030, with sectoral baselines derived from the IPCC 2006 Guidelines (IPCC, 2006).

💡 Key Insight: India’s NDC targets a 33–35 % cut in emissions intensity of GDP by 2030, a benchmark anchored in the IPCC 2006 Guidelines.

[!infographic: "Timeline of major Indian climate‑related statutes and schemes from 1980 to 2022"]<

⚖️ Comparative Analysis: Perform, Achieve and Trade (PAT) Scheme 2012 vs Carbon Trading Scheme 2022

CO2, Methane, Nitrous Oxide: Atmospheric Dynamics & Radiative Forcing

Carbon dioxide (CO₂) concentration reached 417 ppm at Mauna Loa in May 2023 (NOAA, 2023). Atmospheric CO₂ persists for 100–1 000 years because a fraction remains in the oceanic mixed layer, another fraction is sequestered in deep ocean, and the remainder cycles through the biosphere (IPCC, 2021). Radiative forcing from CO₂ equals 1.82 W m⁻² relative to pre‑industrial levels (IPCC, 2021). Primary anthropogenic sources are fossil‑fuel combustion (≈ 78 % of Indian CO₂ emissions), cement manufacture (≈ 12 %), and land‑use change (≈ 10 %) (MoEFCC, 2023). In 2022 India emitted 2.65 Gt CO₂, the fifth‑largest national total (Global Carbon Project, 2023). Sectoral breakdown shows power generation contributing 73 % of national GHG emissions, steel 9 %, and transport 7 % (MoEFCC, 2023). Mitigation pathways rely on renewable‑energy deployment (≈ 190 GW installed by March 2024, Ministry of Power, 2024), carbon capture, utilisation and storage (CCUS) pilots at the Talcher coalfield (Coal India Ltd., 2022), and cement‑kiln optimisation (Cement Manufacturers Association, 2023).

Methane (CH₄) atmospheric mixing ratio stood at 1 910 ppb in 2023 (NOAA, 2023). CH₄ lifetime averages 12.4 years, governed by hydroxyl‑radical (·OH) oxidation, stratospheric loss, and soil uptake (IPCC, 2021). Its 100‑year global warming potential (GWP₁₀₀) is 28 × CO₂ (IPCC, 2021). Radiative forcing from CH₄ amounts to 0.48 W m⁻². Indian CH₄ emissions in 2022 totaled 0.70 Mt CH₄, with agriculture responsible for 45 % (enteric fermentation), waste‑water treatment 22 %, and coal mining 18 % (MoEFCC, 2023). The 2022 Supreme Court judgment in Mahanadi Coalfields Ltd. v. Union of India mandated a methane‑capture plan for underground mines, prompting the Ministry of Coal to commission 30 % capture technology at Jharia (Ministry of Coal, 2022). Agricultural mitigation includes feed‑additive 3‑nitrooxypropanol (3‑NOP) trials reducing enteric CH₄ by 30 % (ICAR, 2023) and alternate wet‑rice cultivation reducing paddy CH₄ emissions by 20 % (ICAR, 2022). Waste‑water methane recovery projects under the Swachh Bharat Mission have captured 1.2 Mt CH₄ cumulatively (CPCB, 2022).

Nitrous oxide (N₂O) mixing ratio reached 332 ppb in 2023 (NOAA, 2023). N₂O lifetime averages 114 years, controlled by photolysis and reaction with ·OH (IPCC,

GHG Policy Trajectory: From 1990 to 2024

India’s first formal climate commitment emerged with the United Nations Framework Convention on Climate Change (UNFCCC) ratified in 1992, obligating the nation to develop an emissions inventory. The 1998 Supreme Court judgment M.C. Mehta v. Union of India mandated the closure of high‑polluting cement kilns, initiating sector‑wide CO₂ curtailment. In 2000, the Ministry of Environment and Forests (MoEF) launched the National Action Plan on Climate Change (NAPCC), delineating eight missions; the National Solar Mission (2009) and National Mission for Enhanced Energy Efficiency (2010) directly targeted CO₂ intensity. The Inter‑Ministerial Group on Climate Change (2008) institutionalised the NAPCC, embedding it in the Planning Commission’s Five‑Year Plans.

💡 Key Insight: The 2015 Nationally Determined Contribution (NDC) was the first Indian climate pledge to embed methane (CH₄) and nitrous oxide (N₂O) baselines alongside CO₂ intensity targets.

The 2013 Perform, Achieve and Trade (PAT) scheme expanded to include thermal power plants, capping CO₂ emissions per megawatt‑hour. The 2015 NDC pledged a 33–35 % reduction in emissions intensity by 2030, integrating methane (CH₄) and nitrous oxide (N₂O) baselines for the first time. Following COP26, the 2021 Methane Emission Reduction Programme (MERP) mandated capture of 70 % of coal‑mine methane, overseen by the Ministry of Coal. Concurrently, the 2022 Nitrogen Management Plan (NMP) required adoption of nitrification inhibitors in paddy cultivation, aiming for a 20 % N₂O cut by 2025.

💡 Key Insight: MERP’s 70 % capture target represents one of the most ambitious coal‑mine methane mitigation commitments globally.

The 2023 Climate Change (Amendment) Bill, passed by Parliament, created a Climate Change Authority to enforce sectoral emission caps and to certify carbon credits. The 2024 National Clean Air Programme (NCAP) revision introduced a CO₂‑specific ambient monitoring grid, expanding the CPCB network to 500 stations. Each milestone reconfigured the governance architecture, shifting from ad‑hoc directives to codified, cross‑ministerial mechanisms that align domestic policy with evolving international obligations.

[!infographic: "Timeline of India’s major GHG‑related policies from 1992 to 2024, showing key legislation, court rulings, and program launches"]<

⚖️ Comparative Analysis: 2015 NDC vs 2021 MERP

📋 Classification: Major Policy Milestones (1992‑2024)

[!infographic: "Flowchart showing how each policy milestone builds on previous mechanisms, illustrating the shift from ad‑hoc directives to cross‑ministerial governance"]<

GHGs: CO₂, Methane, Nitrous Oxide — Significance

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📊 Quick Reference: GHGs: CO2, Methane, Nitrous Oxide

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