Chapter 8 · Topic 8.1 · Prelims + Mains1 of 3
Climate Change: Greenhouse effect and warming
Key points
- Greenhouse effect and gases.
- Global warming and its effects.
- Impacts on India.
10 PYQs 2016–2026
Prelims box: facts and traps
| Greenhouse gas | Main human sources |
|---|---|
| Carbon dioxide (CO2) | Burning coal, oil and gas; cement; deforestation |
| Methane (CH4) | Rice paddies, livestock, landfills, coal mines, gas leaks |
| Nitrous oxide (N2O) | Nitrogen fertilisers, manure, some industry |
| Fluorinated gases (HFCs, PFCs, SF6) | Refrigeration, air conditioning, electrical equipment |
| Water vapour | Not emitted directly in climate terms; rises as the air warms and amplifies warming. |
- decade or two (Prelims 2019: 1, 2 and 3 Prelims 2019).
- The System of Rice Intensification, with alternate wetting and drying of fields, reduces seed requirement, methane production and electricity use for pumping (Prelims 2022: 1, 2, 3).
- The world's largest tropical peatland, holding about three years' worth of global fossil-fuel carbon emissions, lies in the Congo Basin (Prelims 2024).
- Trap (UPSC Prelims 2022): all the statements are correct.
- Trap (UPSC Prelims 2019): all the statements are correct.
On this page (3 sections)
The greenhouse effect and greenhouse gases
Sunlight passes through the atmosphere and warms the Earth’s surface, which gives off heat as infrared radiation. Greenhouse gases absorb part of this infrared and send it back down, keeping the planet far warmer than it would otherwise be. This natural greenhouse effect makes life possible; adding more of these gases strengthens it and warms the planet further.
| Greenhouse gas | Main human sources |
|---|---|
| Carbon dioxide (CO2) | Burning coal, oil and gas; cement; deforestation |
| Methane (CH4) | Rice paddies, livestock, landfills, coal mines, gas leaks |
| Nitrous oxide (N2O) | Nitrogen fertilisers, manure, some industry |
| Fluorinated gases (HFCs, PFCs, SF6) | Refrigeration, air conditioning, electrical equipment |
| Water vapour | Not emitted directly in climate terms; rises as the air warms and amplifies warming |
Methane hydrate deposits: global warming might release methane from them, large deposits lie in the Arctic tundra and under the seafloor, and methane in the atmosphere oxidises to carbon dioxide after a
decade or two (Prelims 2019: 1, 2 and 3 Prelims 2019).
Which of the following statements are correct about the deposits of ‘methane hydrate’? 1. Global warming might trigger the release of methane gas from these deposits. 2. Large deposits of ‘methane hydrate’ are found in Arctic Tundra and under the seafloor. 3. Methane in atmosphere oxidizes to carbon dioxide after a decade or two. Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer
Answer: (d) · UPSC official key
The System of Rice Intensification, with alternate wetting and drying of fields, reduces seed requirement, methane production and electricity use for pumping (Prelims 2022: 1, 2, 3).
“System of Rice Intensification” of cultivation, in which alternate wetting and drying of rice fields is practised, results in : 1. Reduced seed requirement 2. Reduced methane production 3. Reduced electricity consumption Select the correct answer using the code given below :
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2, 3
Show answer
Answer: (d) · UPSC official key
Global warming and its effects
The IPCC’s Sixth Assessment Synthesis Report (2023) states that human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850–1900 in 2011–2020 (IPCC AR6 SYR, SPM headline statement A.1).
| Effect of warming | What happens |
|---|---|
| Hotter extremes | More frequent and intense heatwaves |
| Water cycle | Heavier downpours in places, longer droughts in others |
| Ice | Glaciers retreat; sea ice and ice sheets shrink |
| Oceans | Sea level rise, warming and acidification; coral bleaching |
| Life | Species shift ranges; crop yields and health are affected |
Mains 2022: Discuss global warming and mention its effects on the global climate. Mains 2022 Explain the control measures to bring down the level of greenhouse gases which cause global warming, in the light of the Kyoto Protocol, 1997. The Kyoto Protocol set binding targets only for developed (Annex I) countries and created market mechanisms such as the Clean Development Mechanism.
Discuss global warming and mention its effects on the global climate. Explain the control measures to bring down the level of greenhouse gases which cause global warming, in the light of the Kyoto Protocol, 1997.
The world’s largest tropical peatland, holding about three years’ worth of global fossil-fuel carbon emissions, lies in the Congo Basin (Prelims 2024). Draining or burning peat releases this carbon.
One of the following regions has the world’s largest tropical peatland, which holds about three years worth of global carbon emissions from fossil fuels; and the possible destruction of which can exert detrimental effect on the global climate. Which one of the following denotes that region ?
- Amazon Basin
- Congo Basin
- Kikori Basin
- Rio de la Plata Basin
Show answer
Answer: (b) · UPSC official key
How climate change affects India
India is highly exposed: a long, densely populated coastline, monsoon-dependent farming, Himalayan glaciers feeding the Indus, Ganga and Brahmaputra, and many people in poverty. Heatwaves, erratic monsoon rain, floods, cyclones, glacier retreat and sea level rise all threaten lives, water, food and infrastructure.
| Region | Main risks |
|---|---|
| Himalayan States | Glacier retreat, glacial lake outburst floods, landslides, cloudbursts, changing river flows |
| Coastal States | Sea level rise, stronger cyclones and storm surges, saltwater entering farms and aquifers, mangrove and coral stress |
| Plains and Deccan | Heat stress, drought, falling crop yields, groundwater stress |
Mains 2017: ‘Climate change’ is a global problem. How India will be affected by climate change? How Himalayan and coastal states of India will be affected by climate change? Mains 2017
‘Climate change’ is a global problem. How India will be affected by climate change? How Himalayan and coastal states of India will be affected by climate change?
Mains 2023: The Intergovernmental Panel on Climate Change (IPCC) has predicted a global sea level rise of about one metre by AD 2100. What would be its impact in India and the other countries in the Indian Ocean region? Mains 2023 Think of low-lying deltas such as the Sundarbans, coastal cities, and island nations such as the Maldives.
The Intergovernmental Panel on Climate Change (IPCC) has predicted a global sea level rise of about one metre by AD 2100. What would be its impact in India and the other countries in the Indian Ocean region?
Mains box: analysis and answer points
- Sunlight passes through the atmosphere and warms the Earth's surface, which gives off heat as infrared radiation.
- Greenhouse gases absorb part of this infrared and send it back down, keeping the planet far warmer than it would otherwise be.
- Methane hydrate deposits: global warming might release methane from them, large deposits lie in the Arctic tundra and under the seafloor, and methane in the atmosphere oxidises to carbon dioxide after a
- Likely next angle: Methane hydrates
- Asked: Mains 2022 (GS Paper III, 15 marks): Discuss global warming and mention its effects on the global climate. Explain the control measures to bring down the level of greenhouse gases which cause global warming, in the light of the Kyoto Protocol, 1997.
Practice
Practice MCQs (8)
To express the emission of a non-CO₂ greenhouse gas in 'carbon dioxide equivalent' (CO₂e), its mass is usually multiplied by its:
Answer (a) & explanation
Carbon dioxide equivalent puts different gases on one scale. The mass of a gas is multiplied by its Global Warming Potential (GWP), normally the 100-year value used in national inventories: for example, 1 tonne of nitrous oxide with a GWP of about 273 counts as about 273 tonnes CO₂e. The lifetime of a gas is one input to its GWP but is not itself the multiplier, and the Ozone Depletion Potential measures harm to the ozone layer, not warming.
In the absence of the natural greenhouse effect, the average surface temperature of the Earth would be closest to which one of the following?
Answer (b) & explanation
The present global average surface temperature is about 15 °C. Standard texts estimate that without the natural greenhouse effect the Earth would settle at roughly −18 °C, about 33 °C colder, well below the freezing point of water. The natural greenhouse effect is therefore essential for life; the concern of global warming is the enhanced greenhouse effect caused by extra human emissions.
Consider the following gases:
1. Nitrous oxide
2. Sulphur hexafluoride
3. Argon
4. Nitrogen trifluoride
5. Water vapour
How many of the above are greenhouse gases?
Answer (c) & explanation
Four of the five are greenhouse gases. Nitrous oxide, sulphur hexafluoride and nitrogen trifluoride all absorb infrared strongly and are listed with their global warming potentials in IPCC AR6; water vapour is the most abundant natural greenhouse gas. Argon is a single-atom noble gas: it has no molecular bonds that can vibrate, so it does not absorb infrared, even though it is the third most abundant gas in dry air.
Which one of the following gases is both a long-lived greenhouse gas and, according to UNEP, currently the most significant ozone-depleting substance being emitted by human activities?
Answer (a) & explanation
Nitrous oxide traps heat (100-year GWP of about 270 and a lifetime of about 109 years) and, when it reaches the stratosphere, breaks down into nitrogen oxides that destroy ozone. Because CFCs have been phased out under the Montreal Protocol while nitrous oxide is not controlled by it, UNEP's 2013 report described it as the most significant ozone-depleting substance now emitted. Its main human source is nitrogen fertiliser use in agriculture, along with manure and some industries.
Consider the following greenhouse gases:
1. Nitrous oxide
2. Sulphur hexafluoride
3. Methane
Which one of the following gives their correct sequence in increasing order of atmospheric lifetime?
Answer (b) & explanation
IPCC AR6 gives atmospheric lifetimes of about 11.8 years for methane, about 109 years for nitrous oxide and about 3,200 years for sulphur hexafluoride. So the increasing order is methane → nitrous oxide → sulphur hexafluoride (3-1-2). Methane is removed relatively fast by reaction with hydroxyl radicals, nitrous oxide is destroyed mainly by sunlight in the stratosphere, and sulphur hexafluoride is so stable that it is effectively permanent on human time scales.
With reference to the greenhouse effect, consider the following statements:
1. The Earth's surface radiates energy mainly in the long-wave (infrared) part of the spectrum.
2. Greenhouse gases are largely transparent to incoming short-wave solar radiation but absorb outgoing infrared radiation.
3. Nitrogen and oxygen, the two main constituents of dry air, are significant greenhouse gases.
Which of the statements given above are correct?
Answer (a) & explanation
Statements 1 and 2 are correct. The Sun, being very hot, sends energy mostly as short-wave radiation, which passes through the atmosphere largely unabsorbed. The cooler Earth re-radiates this energy as long-wave (infrared) radiation, and gases such as water vapour, carbon dioxide, methane and nitrous oxide absorb and re-emit it, warming the lower atmosphere — the greenhouse effect. Statement 3 is wrong: nitrogen and oxygen are two- atom symmetric molecules that hardly absorb infrared, so they are not greenhouse gases even though they make up about 99% of dry air.
With reference to the Global Warming Potential (GWP) of greenhouse gases, consider the following statements:
1. GWP compares the warming caused by a given mass of a gas with that caused by the same mass of carbon dioxide over a chosen time horizon.
2. The GWP of methane over a 20-year horizon is higher than its GWP over a 100-year horizon.
3. The 100-year GWP of sulphur hexafluoride is lower than its 20-year GWP.
Which of the statements given above are correct?
Answer (a) & explanation
Statements 1 and 2 are correct. GWP is the heat trapped by 1 kg of a gas, relative to 1 kg of carbon dioxide, integrated over a time horizon (usually 20 or 100 years). Methane survives only about 12 years, so most of its effect is packed into the first two decades: its 20- year GWP (about 80) is far higher than its 100-year GWP (about 27–30 in AR6). Statement 3 is wrong: sulphur hexafluoride lasts about 3,200 years, so its effect keeps accumulating and its 100-year GWP is higher than its 20-year GWP.
Consider the following statements regarding fluorinated greenhouse gases:
1. Sulphur hexafluoride is widely used as an insulating gas in high-voltage electrical switchgear.
2. Nitrogen trifluoride is used in the manufacture of semiconductors and flat-panel displays.
3. Perfluorocarbons such as tetrafluoromethane are released during primary aluminium smelting.
Which of the statements given above are correct?
Answer (d) & explanation
All three statements are correct. Sulphur hexafluoride is an excellent electrical insulator, so it fills high-voltage circuit breakers and gas-insulated switchgear; leaks matter because it is the most potent greenhouse gas assessed by IPCC. Nitrogen trifluoride is used to clean chambers and etch circuits in semiconductor and display factories. Perfluorocarbons (tetrafluoromethane and hexafluoroethane) form during 'anode effects' in aluminium smelting. All of them are extremely long-lived.
0 / 0 correct
Prelims PYQs on this topic (8)
With reference to the Agreement at the UNFCCC Meeting in Paris in 2015, which of the following statements is/are correct?
- 1. The Agreement was signed by all the member countries of the UN and it will go into effect in 2017.
- 2. The Agreement aims to limit the greenhouse gas emissions so that the rise in average global temperature by the end of this century does not exceed 2°C or even 1.5°C above pre-industrial levels.
- 3. Developed countries acknowledged their historical responsibility in global warming and committed to donate $ 1000 billion a year from 2020 to help developing countries to cope with climate change.
Select the correct answer using the code given below.
Answer (b) & explanation
Only statement 2 is correct (b). The Paris Agreement (COP21, 2015) aims to keep the rise in global temperature well below 2°C above pre-industrial levels and to try to limit it to 1.5°C (2). Statement 1 is wrong because it came into force on 4 November 2016, after the 55-country, 55%-of-emissions threshold was crossed. Not every UN member had signed it. Statement 3 is wrong because the finance goal was $100 billion a year, not $1,000 billion, and it was a collective goal, not an admission of historical blame.
At COP29 (Baku, 2024) a new goal (NCQG) of $300 billion a year by 2035 was set. Notice that countries set their own targets (NDCs). India's include net zero by 2070 and 50% non-fossil power capacity, which it reached in 2025.
Watch the zero: the goal was 100 billion dollars, not 1000.
Answer as per the official UPSC answer key.
Consider the following statements with reference to India’s response to climate change :
- I. India’s Long-Term Low Emission Development Strategy (LT-LEDS) is a crucial tool for achieving net-zero emissions by 2070.
- II. India’s 4th Biennial Update Report (BUR-4) submitted in December, 2024 recorded around 8% decrease in Greenhouse gas emissions in 2020 over 2019.
- III. Climate-resilient development necessarily depends on quick and short-term achievement of emission reduction targets.
Which of the following relationships among the above statements is/are correct ?
- 1. Statement I is empirically supported by statement II.
- 2. Statement III contradicts the approach implicit in statement I.
- 3. Statement I and statement III together establish the premise of long-term sustainability.
Select the answer using the code given below :
Answer (b) & explanation
Relationships 1 and 2 are correct (b). Relationship 1 is right: the LT-LEDS (2022) lays out India's path to net zero by 2070, and BUR-4 reported a fall of about 7.9% in 2020 emissions over 2019, real data in line with that path. Relationship 2 is right: Statement III wants quick, short-term cuts, while the LT-LEDS is a long, gradual plan, so III contradicts I. Relationship 3 is wrong: two contradicting statements cannot together set a premise. So options (a), (c) and (d) fail.
Notice the cause of the 2020 fall: the COVID-19 lockdowns, not a lasting trend. India's updated NDC (2022) targets cutting emissions intensity of GDP by 45% from 2005 levels by 2030. Biennial Transparency Reports now replace BURs.
"together establish" sounds positive, but two statements that clash cannot form one premise.
Answer as per the official UPSC answer key.
Which of the following statements in relation to NIRANTAR (National Institute for Research and Application of Natural Resources to Transform, Adapt and Build Resilience), a platform of institutions under the Ministry of Environment, Forest and Climate Change, is/are correct ?
- 1. Ecosystem Survey and Analysis is a vertical under this platform, the lead institute of which is Botanical Survey of India, Kolkata.
- 2. Research and Management of Ecosystem Service is a vertical under this platform, the lead institute of which is Central Zoo Authority, New Delhi.
- 3. Capacity Development Support is a vertical under this platform, the lead institute of which is Indian Institute of Forest Management, Bhopal.
Select the answer using the code given below :
Answer (b) & explanation
Statements 1 and 3 are correct (b). NIRANTAR groups the Environment Ministry's institutes into verticals. Statement 1 is right: Ecosystem Survey and Analysis is led by the Botanical Survey of India, Kolkata, with bodies like the FSI and ZSI. Statement 3 is right: Capacity Development Support is led by the Indian Institute of Forest Management, Bhopal. Statement 2 is wrong: Research and Management of Ecosystem Service is led by ICFRE, Dehradun; the Central Zoo Authority is only a member. So options (a), (c) and (d) fail.
Notice the purpose: pooling institutes avoids duplicate work and links research to climate adaptation and resilience. Other Ministry bodies include the Wildlife Institute of India (Dehradun) and GBPNIHE for the Himalaya.
the Central Zoo Authority does sit in that vertical, but as a member, not the lead.
Answer as per the official UPSC answer key.
Consider the following statements :
- Statement I : At the 28th United Nations Climate Change Conference (COP28), India refrained from signing the ‘Declaration on Climate and Health’.
- Statement II : The COP28 Declaration on Climate and Health is a binding declaration; and if signed, it becomes mandatory to decarbonize health sector.
- Statement III : If India’s health sector is decarbonized, the resilience of its health-care system may be compromised.
Which one of the following is correct in respect of the above statements?
Answer (c) & explanation
Only Statement III is correct and it explains Statement I (c). Statement I is right: India stayed out of the COP28 (Dubai, 2023) Declaration on Climate and Health. Statement III is right and is the reason: India worried that cutting emissions from health care now could limit the growth of its still-expanding health system and its resilience. Statement II is wrong: the declaration is voluntary, not binding; signing it would not make decarbonisation mandatory. So options (a), (b) and (d) fail.
Notice the bigger picture: COP28 also launched the Global Stocktake call to "transition away" from fossil fuels and set up the Loss and Damage Fund. India stresses equity and common but differentiated responsibilities.
"binding" is the error. COP declarations are political pledges, not treaties.
Answer as per the official UPSC answer key.
Consider the following statements :
- Statement I : Article 6 of the Paris Agreement on climate change is frequently discussed in global discussions on sustainable development and climate change.
- Statement II : Article 6 of the Paris Agreement on climate change sets out the principles of carbon markets.
- Statement III : Article 6 of the Paris Agreement on climate change intends to promote inter-country non-market strategies to reach their climate targets.
Which one of the following is correct in respect of the above statements?
Answer (a) & explanation
Both II and III are correct and both explain Statement I (a). Article 6 of the Paris Agreement lets countries work together to meet their targets. Statement II is right: Articles 6.2 and 6.4 set up carbon markets, for trading credits between countries and through a UN-run mechanism. Statement III is right: Article 6.8 covers non-market approaches, such as joint finance, technology and capacity building. Both halves are why it is discussed so much, so options (b), (c) and (d) fail.
Notice the progress: rules for Article 6 carbon markets were finally agreed at COP29 in Baku (2024). India's own Carbon Credit Trading Scheme (2023) builds a domestic market, and India has signed Article 6.2 deals, such as with Japan.
Answer as per the official UPSC answer key.
Which organization has enacted the Nature Restoration Law (NRL) to tackle climate change and biodiversity loss?
Answer (a) & explanation
The European Union enacted the Nature Restoration Law (a). The European Union adopted its Nature Restoration Law in 2024. It requires member states to restore at least 20% of the EU's damaged land and sea areas by 2030, and all ecosystems in need by 2050. Options (b), (c) and (d) are wrong: only a body that makes laws can "enact" one. The World Bank, OECD and FAO give loans, advice or technical help, but cannot pass binding laws.
Notice the link to the Kunming-Montreal Global Biodiversity Framework (2022), whose "30 by 30" target asks for 30% of land and sea to be protected by 2030. The EU law faced strong protests from farmers before it passed narrowly.
Answer as per the official UPSC answer key.
Mains PYQs on this topic (2)
- UPSC Mains 2025 · GS Paper III · Q7What is Carbon Capture, Utilization and Storage (CCUS) ? What is the potential role of CCUS in tackling climate change ?How to approach: Intro: definition. Body: (1) Process; (2) Role in climate action; (3) India; (4) Limits. Conclusion: CCUS is a complement, not a substitute, for renewables and…
- UPSC Mains 2023 · GS Paper III · Q18The Intergovernmental Panel on Climate Change (IPCC) has predicted a global sea level rise of about one metre by AD 2100. What would be its impact in India and the other countries in the Indian Ocean region?How to approach: Intro: IPCC AR6 projections; causes: thermal expansion, ice melt. Body: (1) India: coastal flooding of cities (Mumbai, Kolkata, Chennai), Sundarbans and deltas,…
Write an answer
In 150 words, explain the significance of Climate Change with one recent example.
Flashcards (5)
What do greenhouse gases absorb?
Outgoing infrared radiation.
Practice that cuts paddy methane?
Alternate wetting and drying (SRI).
Warming in 2011–2020 vs 1850–1900
(IPCC)? 1.1°C.
World's largest tropical peatland?
Congo Basin.
Kyoto Protocol year?
1997.
Read more: related explainers
In the news
- 22 Oct 2026GRAP Stage I invoked in Delhi-NCR as AQI turns ‘Poor’: the 25 actions and what comes next
- 20 Oct 2026National Red List of birds: 1,211 species under assessment, 107 done in first review
- 16 Oct 2026CAQM orders PTZ cameras at all polluting industries in NCR by 30 November 2026
- 15 Oct 2026Sukhna Wetland and Sauj Jheel become Ramsar sites; India’s tally reaches 103
Next topic · 8.2 →Climate Change: Sinks, capture and carbon marketsSyllabus: GS-III · Conservation, environmental pollution and degradation, environmental impact asse…