These notes cover climate change and ozone depletion for OPSC/OAS prelims and mains in the current policy context: the physical science of warming and ozone loss, observed impacts, adaptation and mitigation, India’s targets and carbon market, the Montreal–Kigali regime, and Odisha’s state climate action plan. Outdated figures from older question banks have been replaced with IPCC AR6, WMO 2024–25 and COP29 outcomes.
Climate Change: Science and Attribution
Climate change refers to a change of climate attributed directly or indirectly to human activity that alters the composition of the global atmosphere, in addition to natural variability. 2024 The IPCC Sixth Assessment Report (AR6, 2023) concluded that human activities have unequivocally caused global warming, with the global surface temperature reaching 1.1°C above 1850–1900 levels during 2011–2020. IPCC AR6 2023 OPSC 2022
Greenhouse gases are transparent to incoming shortwave solar radiation but absorb outgoing longwave infrared radiation emitted by the Earth’s surface. Without the natural greenhouse effect, the Earth’s average surface temperature would be about −18°C; with it, about 15°C. UPPSC 2020 CDS 2012
The dominant anthropogenic greenhouse gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and fluorinated gases. Water vapour is the most abundant greenhouse gas and contributes the largest share of the natural greenhouse effect, but its concentration is a feedback, not a direct emission control. OPSC 2018 Carbon dioxide remains the most important driver of long-term warming because of its abundance and persistence.
| Gas | Dominant anthropogenic source |
|---|---|
| Carbon dioxide | Fossil fuel combustion; cement production |
| Methane | Enteric fermentation; paddy fields; landfills; coal mining |
| Nitrous oxide | Nitrogen fertilisers; industrial processes |
| Fluorinated gases (HFCs, PFCs, SF₆) | Refrigeration, air-conditioning, industrial applications |
Black carbon is a short-lived climate forcer: it absorbs sunlight strongly, has an atmospheric lifetime of days to weeks, and is emitted by diesel engines, brick kilns and biomass burning. 2024 It is not a greenhouse gas but a warming aerosol.
- Oxygen (O₂) and nitrogen (N₂) are not greenhouse gases; their molecular structure does not absorb infrared radiation. NDA 2015
- CFCs are both ozone-depleting and potent greenhouse gases; the two problems are linked but distinct.
Observed and Projected Impacts
Warming has already increased the frequency and intensity of heatwaves, heavy precipitation, droughts and tropical cyclones. 2024 Sea-level rise is driven by thermal expansion of ocean water and the melting of glaciers and ice sheets. CDS 2016 The rate and magnitude are not uniform across coastlines; local subsidence and ocean circulation cause regional differences.
At 1.5°C of warming, coral reefs face severe degradation; at 2°C, almost all warm-water corals are at high risk. The IPCC AR6 finds that every increment of warming intensifies multiple and concurrent hazards. IPCC AR6 2023 Projected impacts include reduced crop yields in tropical regions, increased vector-borne disease transmission, and displacement of coastal communities.
Higher atmospheric CO₂ can increase photosynthesis and plant growth, but the effect is constrained by water and nutrients. IAS (Pre) 2018
Adaptation, Mitigation and Carbon Markets
Adaptation reduces vulnerability to climate impacts; mitigation reduces greenhouse gas emissions or enhances sinks. 2024 India’s National Action Plan on Climate Change (NAPCC, 2008) originally comprised eight national missions covering solar power, enhanced energy efficiency, sustainable habitat, water, the Himalayan ecosystem, sustainable agriculture, health, and strategic knowledge. UPPSC (Pre) 2018
India’s updated Nationally Determined Contribution (NDC, 2022) commits to reducing the emissions intensity of GDP by 45% by 2030 from 2005 levels and achieving 50% cumulative electric power installed capacity from non-fossil fuel sources by 2030. 2022 India’s long-term target is net-zero by 2070. 2024 As of February 2026, non-fossil sources already account for 52.57% of installed electricity capacity, and emissions intensity fell by 36% between 2005 and 2020. 2026
India’s Carbon Credit Trading Scheme (CCTS), 2023
The CCTS was notified in June 2023 under the Energy Conservation Act, 2001 (amended 2022), and is administered by the Bureau of Energy Efficiency under the Ministry of Power. 2023 It is an intensity-based baseline-and-credit system: obligated entities receive a target in tCO₂e per unit of product, set for three years at a time. 2025 The first compliance period covers seven energy-intensive sectors (aluminium, cement, chlor-alkali, pulp and paper, petroleum refining, petrochemicals, and textiles) from FY2026, with approximately 490 entities. 2026 A voluntary offset mechanism was notified in December 2023. 2025
- CCTS is administered by the Ministry of Power, not the Ministry of Environment, Forest and Climate Change. 2023
- India has not signed the Global Methane Pledge, which targets a 30% reduction by 2030 from 2020 levels. 2025
Global Climate Governance: From UNFCCC to COP29
The UNFCCC was adopted at the Rio Earth Summit in 1992 and entered into force in 1994. IAS (Pre) 2010 The Kyoto Protocol (1997) set binding targets for Annex-I developed countries and introduced the Clean Development Mechanism (CDM), under which developing countries host emission-reduction projects. IAS (Pre) 2008 One carbon credit equals one tonne of CO₂ equivalent. CDS 2017
The Paris Agreement (2015) replaced the top-down Kyoto approach with nationally determined contributions (NDCs), a global stocktake every five years, and the long-term goal of keeping warming well below 2°C and pursuing 1.5°C. 2024
| Outcome | Key fact |
|---|---|
| COP27, Sharm el-Sheikh (2022) | Agreement to establish a Loss and Damage Fund |
| COP28, Dubai (2023) | Operationalised the Loss and Damage Fund; first global stocktake concluded |
| COP29, Baku (2024) | New Collective Quantified Goal (NCQG): developed countries to lead with USD 300 billion per year by 2035, with an overall aspiration of USD 1.3 trillion per year 2024 |
India expressed disappointment with the COP29 finance outcome, calling USD 300 billion insufficient relative to the needs of developing countries. 2024
Ozone Depletion: Science and the Montreal Protocol
Stratospheric ozone (O₃) absorbs harmful ultraviolet-B and ultraviolet-C radiation. It is concentrated between 15 and 35 km in the stratosphere. UPPSC (Pre) 2018 Tropospheric ozone, by contrast, is an air pollutant and greenhouse gas. The thickness of the ozone layer is measured in Dobson Units. 2024
Ozone depletion is driven by chlorine- and bromine-containing ozone-depleting substances (ODS), chiefly chlorofluorocarbons (CFCs), halons, carbon tetrachloride and methyl chloroform. UPPSC 2012 The Antarctic ozone hole forms in spring because polar stratospheric clouds in the extremely cold winter provide surfaces for chlorine activation; sunlight then catalyses ozone destruction. IAS (Pre) 2011
The Montreal Protocol (1987), under the Vienna Convention (1985), phases out ozone-depleting substances. It has universal ratification and is considered the most successful multilateral environmental agreement. 2024
The Kigali Amendment (2016) extends the Montreal Protocol to phase down hydrofluorocarbons (HFCs), which are potent greenhouse gases used as CFC substitutes. It is expected to avoid up to 0.5°C of warming by 2100. 2024 India ratified the Kigali Amendment in 2021 and, as an Article 5, Group 2 party, will freeze HFC consumption in 2028, then reduce to 90% of baseline by 2032, 80% by 2037, 70% by 2042 and 15% by 2047. 2025
The WMO Ozone Bulletin reports that the 2024 and 2025 Antarctic ozone holes were among the smallest since the early 1990s, and the ozone layer is on track for full recovery within several decades. WMO 2026
Odisha Angle: Climate Vulnerability and State Action
Odisha has a coastline of about 574 km and is exposed to cyclones, storm surges, coastal erosion, floods, droughts and heatwaves. The India Meteorological Department has recorded prolonged heatwaves of five or more consecutive days in Odisha in recent years, including in 2023 and 2024. 2024
Odisha’s State Action Plan on Climate Change (SAPCC) 2021–30 is the first and only state plan to have received approval for that period; a Climate Resilience Cell was inaugurated at Krushi Bhavan in 2024 to implement and monitor it. 2024 The SAPCC identifies sea-level rise, increased storm intensity, extreme droughts, heatwaves, and coastal flooding as the state’s principal climate risks. 2024
| Odisha climate indicator | Data / policy |
|---|---|
| Coastline | About 574 km 2024 |
| Heatwave exposure | Prolonged heatwaves (5+ consecutive days) in recent years, including 2023 and 2024 2024 |
| SAPCC | 2021–30, the first approved state plan for the period; Climate Resilience Cell at Krushi Bhavan 2024 |
| Blue carbon | Bhitarkanika mangroves are a significant coastal carbon sink |
IMAGE (Map): Map of Odisha showing climate-vulnerable districts and the SAPCC risk zones.
Labels: Coastal districts (Balasore, Bhadrak, Kendrapara, Jagatsinghpur, Puri, Ganjam) marked for cyclones and storm surge; inland districts (Bolangir, Kalahandi, Nuapada, Bargarh) marked for drought and heatwave; Bhitarkanika mangrove area.
Caption: Odisha’s climate risk profile under SAPCC 2021–30.
Find it: Odisha Climate Change Cell (climatechangecellodisha.org) SAPCC maps; or draw from the district names in these notes.
Practice Questions
IPCC AR6 2023 According to the IPCC Sixth Assessment Report, the global surface temperature during 2011–2020 was approximately how much above the 1850–1900 baseline?
- 0.6°C
- 0.8°C
- 1.1°C
- 1.5°C
Show answer
(c) – AR6 states that the global surface temperature reached 1.1°C above 1850–1900 during 2011–2020. IPCC AR6 2023
Consider the following statements about India’s updated NDC (2022):
- India commits to reduce the emissions intensity of GDP by 45% by 2030 from 2005 levels.
- India aims for 50% cumulative electric power installed capacity from non-fossil sources by 2030.
- India’s net-zero target year is 2050.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(b) – Statements 1 and 2 are correct. India’s net-zero target is 2070, not 2050. 2022
IAS (Pre) 2011 The formation of the Antarctic ozone hole is most closely associated with which of the following?
- Tropospheric turbulence and CFCs
- Polar stratospheric clouds and CFCs
- Methane and tropospheric ozone
- Global warming and increased polar temperatures
Show answer
(b) – Polar stratospheric clouds in the cold Antarctic winter activate chlorine from CFCs; spring sunlight then drives ozone destruction. IAS (Pre) 2011
The Kigali Amendment to the Montreal Protocol primarily aims to
- Phase out CFCs
- Phase down hydrofluorocarbons (HFCs)
- Reduce methane emissions from agriculture
- Protect biodiversity hotspots
Show answer
(b) – Kigali targets HFCs, which are potent greenhouse gases used as refrigerants. 2024
Consider the following statements about the Carbon Credit Trading Scheme (CCTS):
- It was notified in 2023 under the Energy Conservation Act.
- It is an intensity-based baseline-and-credit system.
- It is administered by the Ministry of Environment, Forest and Climate Change.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
(b) – Statements 1 and 2 are correct. CCTS is administered by the Ministry of Power/Bureau of Energy Efficiency, not MoEFCC. 2023
Which of the following statements about Odisha’s State Action Plan on Climate Change (SAPCC) 2021–30 is correct?
- It is limited to coastal districts only
- Odisha is the first and only state to get approval for its SAPCC for 2021–30
- It focuses exclusively on mitigation
- It has not been operationalised
Show answer
(b) – Odisha’s SAPCC 2021–30 is the first and only state plan approved for that period; a Climate Resilience Cell was set up in 2024. 2024
At COP29, the New Collective Quantified Goal (NCQG) on climate finance set which target?
- USD 100 billion per year by 2025
- USD 300 billion per year by 2035 from developed to developing countries
- USD 1 trillion per year by 2030
- USD 50 billion per year by 2030
Show answer
(b) – COP29 set the NCQG at USD 300 billion per year by 2035, with an overall aspiration of USD 1.3 trillion per year. 2024
India has NOT signed which of the following international initiatives?
- Paris Agreement
- Kigali Amendment
- Global Methane Pledge
- Montreal Protocol
Show answer
(c) – India has not signed the Global Methane Pledge, which targets a 30% reduction by 2030 from 2020 levels, largely due to its dependence on agriculture. 2025