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Greenhouse gases, global warming and the ozone layer

తెలుగులో వివరణ

Climate change · Part 1 / 3 · Fact-checked on 8 November 2026 · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

How the greenhouse effect works; the main greenhouse gases, their sources and global warming potentials; observed warming, feedbacks and impacts; the stratospheric ozone layer, the chemicals that destroy it and the Antarctic ozone hole; the Vienna Convention, the Montreal Protocol and the Kigali Amendment, with India's commitments.

Each idea is explained first in Telugu (తెలుగు), ending with the English and Hindi exam terms, followed by the same point in exam English. UPSC Prelims is in English or Hindi, so understand it in Telugu and revise it in English.

ఈ అధ్యాయంలో రెండు వేర్వేరు సమస్యలు ఉన్నాయి. ఒకటి భూతాపం: కింది గాలిలో కార్బన్ డయాక్సైడ్ లాంటి వాయువులు వేడిని పట్టి ఉంచడం, దుప్పటి ఒంటి వేడిని బయటకు పోనివ్వనట్టు. రెండోది ఓజోన్ పొర పలచబడటం: ఇది చాలా పైన, స్ట్రాటోస్ఫియర్‌లో, క్లోరిన్, బ్రోమిన్ వల్ల జరుగుతుంది. ఇవి రెండూ ఒకటే అనుకోవద్దు; కొన్ని రసాయనాలు మాత్రమే రెండింటినీ కలుపుతాయి. (→ English: global warming; ozone layer; stratosphere · हिन्दी: वैश्विक तापन; ओज़ोन परत; समतापमंडल)

In exam EnglishClimate change is taught in three parts. This first part is the science: how a few gases keep the Earth warm, which of them human activity is adding, how much the planet has already warmed and what that does. It also covers a second, separate problem, the thinning of the ozone layer, and the treaty that turned it around. Parts 2 and 3 cover the climate treaties and India's plans. global warming is about heat trapped in the lower air by gases such as carbon dioxide. Ozone loss happens much higher, in the stratosphere, and is caused by chlorine and bromine. A few chemicals connect the two stories, and Prelims questions like to test exactly those links.

హరితగృహ ప్రభావం అంటే ఇలా: ఎండలో ఆపిన కారు అద్దాలు మూసి ఉంటే లోపల వేడి పెరుగుతుంది. సూర్యకాంతి సులువుగా లోపలికి వస్తుంది, నేల వేడెక్కి ఆ వేడిని పైకి పంపుతుంది, కానీ హరితగృహ వాయువు కొంత వేడిని తిరిగి కిందికి పంపుతుంది. ఈ సహజ దుప్పటి లేకపోతే భూమి మంచులా గడ్డకట్టేది. గాలిలో ఎక్కువగా ఉండే నైట్రోజన్, ఆక్సిజన్ ఈ పని చేయవు. మనుషులు ఇంకా వాయువులు కలిపితే దుప్పటి మందమై భూతాపం వస్తుంది. (→ English: greenhouse effect; greenhouse gas; global warming · हिन्दी: हरितगृह प्रभाव; हरितगृह गैस; वैश्विक तापन)

In exam EnglishThe greenhouse effect begins with sunlight. Most solar energy arrives as short-wave radiation that passes easily through the air and warms the ground and the sea. A warm surface then gives off its own energy as long-wave infrared. A greenhouse gas absorbs part of this outgoing infrared and sends much of it back towards the surface, so the lower atmosphere holds more heat than it otherwise would. Without this natural blanket the Earth's average surface temperature would be roughly minus 18 °C rather than about 15 °C. Nitrogen and oxygen, which together make up about 99 per cent of dry air, hardly absorb infrared at all; the trapping is done by gases present in small amounts. The problem today is the enhanced effect: extra gases added by people thicken the blanket, and that drives global warming.

జలబాష్పం సహజంగా ఎక్కువ వేడిని పడుతుంది, కానీ అది ఉష్ణోగ్రతను అనుసరిస్తుంది, మనం నేరుగా పెంచం. మనం పెంచే ముఖ్య హరితగృహ వాయువు కార్బన్ డయాక్సైడ్: బొగ్గు, పెట్రోల్ కాల్చడం, సిమెంట్, అడవులు నరకడం. మీథేన్ పశువుల కడుపు, నీరు నిలిచిన వరి పొలాలు, చెత్త దిబ్బల నుంచి వస్తుంది. నైట్రస్ ఆక్సైడ్ ఎరువులు వేసిన నేల నుంచి. ఫ్రిజ్, ఏసీలలో వాడే ఫ్లోరిన్ వాయువులు కొంచెమే అయినా చాలా బలమైనవి. (→ English: greenhouse gas; carbon dioxide; methane; nitrous oxide · हिन्दी: हरितगृह गैस; कार्बन डाइऑक्साइड; मीथेन; नाइट्रस ऑक्साइड)

In exam EnglishWater vapour is the largest natural contributor to the greenhouse effect, but people do not control it directly: its amount follows temperature, so it acts as an amplifier rather than a starting push. Carbon dioxide is the main gas released by human activity, chiefly from burning coal, oil and gas, from making cement and from clearing forests. Before the industrial era its concentration was about 280 parts per million; NOAA's annual average at Mauna Loa in Hawaii passed 420 parts per million for the first time in 2023. Methane comes from livestock digestion, flooded rice fields, landfills, wetlands, coal mines and leaking gas pipes. Nitrous oxide comes mostly from fertilised soils and manure. The fluorinated gases, namely hydrofluorocarbons (HFCs), perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride, are purely industrial and released in small quantities, yet each tonne traps a great deal of heat. Ozone near the ground also acts as a greenhouse gas.

ఒక్కో వాయువు బలం వేరు, అందుకే భూతాప సామర్థ్యం అనే కొలబద్ద. కార్బన్ డయాక్సైడ్‌కు 1 అనుకుంటే, ఒక టన్ను మీథేన్ 100 ఏళ్లలో సుమారు 28 టన్నుల కార్బన్ డయాక్సైడ్ అంత వేడి పడుతుంది. రూపాయి, డాలర్, యెన్‌లను ఒకే కరెన్సీలోకి మార్చి కూడినట్టు, అన్ని వాయువులను కార్బన్ డయాక్సైడ్ సమానంలోకి మార్చి కలుపుతారు. మీథేన్ త్వరగా విడిపోతుంది, కాబట్టి 20 ఏళ్ల లెక్కలో దాని సంఖ్య ఇంకా పెద్దది. మసి మంచును నల్లగా చేసి ఆల్బిడో తగ్గిస్తుంది. (→ English: global warming potential; carbon dioxide equivalent; albedo · हिन्दी: वैश्विक तापन क्षमता; कार्बन डाइऑक्साइड समतुल्य; ऐल्बिडो)

In exam EnglishBecause the gases differ so much in strength, scientists compare them with a single yardstick, the global warming potential. It measures how much heat one tonne of a gas traps over a chosen period, usually 100 years, relative to one tonne of carbon dioxide, which is fixed at 1. In the IPCC's Fifth Assessment Report (2013) methane scores about 28, nitrous oxide about 265 and sulphur hexafluoride about 23,500. Multiplying each gas by its score gives emissions in carbon dioxide equivalent, which is how national targets add different gases together. The time window matters: methane breaks down in about twelve years, so over 20 years its score rises to about 84. That is why cutting methane, HFCs and black carbon (soot) is seen as the fastest way to slow warming; black carbon also darkens snow and ice and lowers their albedo.

The main greenhouse gases compared (global warming potentials over 100 years, IPCC Fifth Assessment Report, 2013)
Gas	Main human sources	Stays in the air	GWP (100 years)
Carbon dioxide	Coal, oil and gas; cement; deforestation	Centuries and longer	1 (by definition)
Methane	Livestock, rice paddies, landfills, coal and gas	About 12 years	About 28
Nitrous oxide	Fertilised soils, manure, some industry	More than a century	About 265
HFCs	Refrigerators and air-conditioners	Years to decades, by type	Hundreds to over 12,000
Sulphur hexafluoride	Electrical switchgear	Thousands of years	About 23,500

2011–2020లో భూమి సగటు ఉష్ణోగ్రత 1850–1900 కంటే సుమారు 1.1 డిగ్రీలు ఎక్కువ; దీనికి మనుషులే కారణమని ఐపీసీసీ స్పష్టంగా చెప్పింది. ఆర్కిటిక్ రెండింతల కంటే వేగంగా వేడెక్కుతోంది. ఎందుకు? తెల్ల చొక్కా ఎండలో చల్లగా, నల్ల చొక్కా వేడిగా ఉంటుంది కదా. తెల్లటి మంచు కరిగితే కింద ఉన్న నల్లని నీరు ఎక్కువ ఎండను పీలుస్తుంది, ఆల్బిడో తగ్గుతుంది, వేడి ఇంకా పెరుగుతుంది. ఇలా ఒక మార్పు ఇంకో మార్పును పెంచడమే ఫీడ్‌బ్యాక్. (→ English: albedo; feedback; Arctic amplification · हिन्दी: ऐल्बिडो; प्रतिपुष्टि; आर्कटिक प्रवर्धन)

In exam EnglishHow much has the world warmed? The IPCC's Sixth Assessment Report (Working Group I, 2021) found that global surface temperature in 2011–2020 was about 1.1 °C higher than in 1850–1900, and called it unequivocal that human influence has warmed the atmosphere, ocean and land. Warming is uneven. Land heats faster than the ocean, and the Arctic has warmed at more than twice the global rate. Part of the reason lies in feedbacks, changes that a little warming sets off and that then add more warming. When bright sea ice melts, dark water beneath it absorbs more sunlight, so a falling albedo feeds the heat. Thawing permafrost can release stored carbon as carbon dioxide and methane. Warmer air holds more water vapour, itself a heat-trapping gas.

వేడి నీళ్ల గిన్నె పొంగినట్టు, సముద్రపు నీరు వేడెక్కితే వ్యాకోచిస్తుంది; హిమానీనదాలు కరిగి ఇంకా నీరు కలుస్తుంది, అందుకే సముద్రమట్టం పెరుగుతుంది. సముద్రం కార్బన్ డయాక్సైడ్ పీల్చి పుల్లగా మారుతుంది; పగడాలు, ఆల్చిప్పలకు గూడు కట్టుకోవడం కష్టం. మన దేశంలో వడగాలులు, అకాలపు వర్షాలు, పంట నష్టం, తీర గ్రామాలకు ముప్పు. తక్కువ కాలుష్యం చేసిన పేదలే ఎక్కువ నష్టపోతారు. (→ English: sea-level rise; ocean acidification; coral bleaching · हिन्दी: समुद्र-स्तर वृद्धि; महासागरीय अम्लीकरण; प्रवाल विरंजन)

In exam EnglishThe effects reach well beyond hotter days. Sea level rises for two reasons: seawater expands as it warms, and melting glaciers and ice sheets add water. The IPCC (2021) put the rise in global mean sea level at about 0.20 metres between 1901 and 2018, with the pace speeding up. The ocean also soaks up roughly a quarter of the carbon dioxide people emit, which makes seawater more acidic; ocean acidification makes it harder for corals, shellfish and some plankton to build their shells and skeletons, while marine heatwaves bleach coral reefs. Heatwaves and heavy downpours grow more intense, and Himalayan and other mountain glaciers are shrinking. For India this means harsher summers, a less predictable monsoon, risk to crop yields and greater danger to low-lying coasts. The burden falls hardest on those who contributed least, the root of the fairness debate in Part 2.

ఓజోన్ పొర భూమికి గొడుగు లాంటిది. స్ట్రాటోస్ఫియర్‌లో, సుమారు 15 నుంచి 35 కిలోమీటర్ల ఎత్తులో ఉండి, సూర్యుని ప్రమాదకర అతినీలలోహిత కిరణాలను ఆపుతుంది; లేకపోతే చర్మ క్యాన్సర్, కంటి శుక్లాలు, పంటలకు హాని. ఓజోన్ 220 డాబ్సన్ యూనిట్ల కంటే తగ్గిన చోటును ఓజోన్ రంధ్రం అంటారు. అదే ఓజోన్ నేల దగ్గర ఉంటే వాహనాల పొగతో ఏర్పడి ఊపిరితిత్తులకు హానికరం. పైన రక్షకుడు, కింద శత్రువు. (→ English: ozone layer; stratosphere; ozone hole; ultraviolet · हिन्दी: ओज़ोन परत; समतापमंडल; ओज़ोन छिद्र; पराबैंगनी)

In exam EnglishNow the second problem. The ozone layer is the part of the stratosphere, mostly between about 15 and 35 kilometres up, where ozone (O3) is most concentrated. It absorbs nearly all of the Sun's most dangerous ultraviolet rays and most UV-B, shielding living things from sunburn, skin cancer and cataracts and protecting crops and ocean plankton. Column ozone is measured in Dobson units, and scientists speak of an ozone hole where the total falls below 220 Dobson units. The same molecule plays two opposite roles depending on where it is. High up it is a shield; near the ground, formed from traffic fumes in sunlight, it is a lung-damaging pollutant and a heat-trapping gas.

ఓజోన్ క్షయకారక పదార్థం అంటే పాత ఫ్రిజ్‌ల సీఎఫ్‌సీలు, అగ్నిమాపక యంత్రాల హాలోన్‌లు వంటివి. ఇవి చాలా ఏళ్లు చెడిపోకుండా నెమ్మదిగా స్ట్రాటోస్ఫియర్‌కు చేరి, అతినీలలోహిత కాంతికి విరిగి క్లోరిన్‌ను వదులుతాయి. ఒక్క క్లోరిన్ అణువు, అలసిపోని దొంగలా, వేల ఓజోన్ అణువులను ఒకదాని తర్వాత ఒకటి పాడుచేస్తుంది. అంటార్కిటికాలో చలికాలం చల్లని మేఘాలు ఏర్పడి, సెప్టెంబర్-అక్టోబర్‌లో ఎండ రాగానే ఓజోన్ రంధ్రం తెరుచుకుంటుంది. (→ English: ozone-depleting substance; CFC; polar stratospheric clouds; ozone hole · हिन्दी: ओज़ोन क्षयकारी पदार्थ; CFC; ध्रुवीय समतापमंडलीय बादल; ओज़ोन छिद्र)

In exam EnglishAn ozone-depleting substance is any chemical that, once it reaches the stratosphere, frees chlorine or bromine there. The best known are chlorofluorocarbons (CFCs), once used in refrigerators, air-conditioners, aerosol sprays and foams; halons in fire extinguishers; carbon tetrachloride and methyl chloroform used as solvents; methyl bromide, a fumigant for soil and stored grain; and the milder hydrochlorofluorocarbons (HCFCs). They are very stable: they survive for years, drift slowly upwards, and are finally broken apart by strong ultraviolet light, setting chlorine or bromine free. A single chlorine atom then destroys many thousands of ozone molecules in turn, and bromine is even more destructive atom for atom. The worst damage is over Antarctica. In the dark polar winter a cold whirl of winds, the polar vortex, lets polar stratospheric clouds form; on them chlorine turns into active forms, and when sunlight returns in September and October the ozone hole opens quickly.

మొదట 1985 వియన్నా ఒప్పందం: "కలిసి పని చేద్దాం" అనే మాట మాత్రమే, కోతలు లేవు. తర్వాత 1987లో మాంట్రియల్ ప్రోటోకాల్: ఏ ఓజోన్ క్షయకారక పదార్థం ఎప్పటికి ఆపాలో గడువులు పెట్టింది, పేద దేశాలకు ఎక్కువ సమయం, ఒక నిధి నుంచి డబ్బు ఇచ్చింది. ప్రపంచంలో ప్రతి దేశం సంతకం చేసి ఆమోదించిన మొదటి ఒప్పందాలు ఇవే. మన దేశం 1992లో చేరింది, 2000 నియమాలతో అమలు చేస్తోంది. పొర 2066 నాటికి అంటార్కిటికాపై కోలుకుంటుందని అంచనా. (→ English: Vienna Convention; Montreal Protocol; ozone-depleting substance · हिन्दी: वियना अभिसमय; मॉन्ट्रियल प्रोटोकॉल; ओज़ोन क्षयकारी पदार्थ)

In exam EnglishThe world answered in two steps. The Vienna Convention for the Protection of the Ozone Layer (1985) was a framework: countries agreed to cooperate on research and to act, without fixing cuts. News of the Antarctic hole that same year, from British Antarctic Survey scientists, added urgency, and the Montreal Protocol was adopted on 16 September 1987 and came into force on 1 January 1989. It set deadlines to phase out the production and use of each ozone-depleting substance and gave developing countries extra years plus money from a Multilateral Fund created by the London Amendment of 1990. In 2009 the Vienna Convention and the Montreal Protocol became the first treaties in UN history to be ratified by every country. India joined the Protocol in 1992 and enforces it through the Ozone Depleting Substances (Regulation and Control) Rules, 2000, made under the Environment (Protection) Act. The WMO–UNEP assessment of 2022 expects the layer to recover to 1980 levels by about 2066 over Antarctica, 2045 over the Arctic and 2040 elsewhere.

సీఎఫ్‌సీలకు బదులు వచ్చిన హెచ్‌ఎఫ్‌సీలు ఓజోన్‌ను పాడుచేయవు, కానీ బలమైన హరితగృహ వాయువులు; ఒక గుంత పూడ్చి ఇంకో గుంత తవ్వినట్టు. అందుకే 2016 కిగాలీ సవరణ మాంట్రియల్ ప్రోటోకాల్‌లోకి హెచ్‌ఎఫ్‌సీలను తెచ్చి, సుమారు 85% వరకు తగ్గించమంది, పూర్తిగా ఆపమనలేదు. మన దేశం 2028లో వాడకాన్ని నిలిపి, 2047 నాటికి 85% తగ్గించాలి. 2019 భారత శీతలీకరణ కార్యాచరణ ప్రణాళిక ఏసీ, ఫ్రిజ్, శీతల గిడ్డంగుల అవసరాన్ని ముందే ఆలోచిస్తుంది. (→ English: Kigali Amendment; Montreal Protocol; HFC phase-down · हिन्दी: किगाली संशोधन; मॉन्ट्रियल प्रोटोकॉल; HFC की चरणबद्ध कमी)

In exam EnglishSuccess created a new problem. Many replacements for CFCs and HCFCs were hydrofluorocarbons, which contain no chlorine and so leave ozone alone, but which are powerful greenhouse gases, and demand for cooling was soaring. The Kigali Amendment to the Montreal Protocol, agreed in Kigali, Rwanda, in October 2016 and in force from 1 January 2019, brought HFCs under the Protocol for a phase-down of about 80–85 per cent, not a total phase-out. Countries move in three groups. Most developed countries began cutting in 2019; China and most developing countries froze consumption in 2024; India, together with Pakistan, Iran, Iraq and the Gulf states, freezes in 2028 against a 2024–2026 baseline and must reach an 85 per cent cut by 2047. India ratified the amendment in 2021, and its India Cooling Action Plan (March 2019) looks twenty years ahead at cooling needs across buildings, transport, cold chains and refrigerants.

మొత్తం చూస్తే: భూతాపం కింది గాలి సమస్య, ఓజోన్ పొర పలచబడటం పై పొర సమస్య. సీఎఫ్‌సీలు రెండూ చేశాయి, అందుకే మాంట్రియల్ ప్రోటోకాల్ భూతాపాన్నీ తగ్గించింది. హెచ్‌ఎఫ్‌సీలను ఇప్పుడు కిగాలీ సవరణ చూసుకుంటుంది. ఓజోన్ సమస్య తేలికగా తీరింది, ఎందుకంటే కొన్ని పరిశ్రమలే మారాలి; కానీ కార్బన్ డయాక్సైడ్ వంట, ప్రయాణం, కరెంటు, అన్నింటి నుంచీ వస్తుంది. ఇంట్లో ఒక పాడైన స్విచ్ మార్చడం సులువు, మొత్తం జీవనశైలి మార్చడం కష్టం. (→ English: global warming; ozone layer; Montreal Protocol; Kigali Amendment · हिन्दी: वैश्विक तापन; ओज़ोन परत; मॉन्ट्रियल प्रोटोकॉल; किगाली संशोधन)

In exam EnglishPutting the part together: global warming and ozone depletion are different problems in different layers, caused by different gases and handled by different treaties, yet they meet at two points. CFCs did double harm, thinning the ozone layer and trapping heat, so the Montreal Protocol also slowed warming. HFCs, the cure for ozone loss, became a climate problem that the Kigali Amendment now handles. The ozone story succeeded because substitutes existed and only a few industries had to change, while carbon dioxide comes from almost everything an economy does. That contrast explains why the climate treaties in the next two parts were much harder to negotiate, and why the question of who should cut first became central.

Global warming and ozone depletion side by side
Feature	Global warming	Ozone depletion
Where it starts	Heat trapped in the lower atmosphere	Ozone destroyed in the stratosphere
Main culprits	Carbon dioxide, methane, nitrous oxide, F-gases	CFCs, halons, carbon tetrachloride, methyl bromide, HCFCs
Key harm	Higher temperatures, rising seas, extremes	More ultraviolet radiation at the surface
Treaties	UNFCCC (1992), Kyoto (1997), Paris (2015)	Vienna (1985), Montreal (1987), Kigali (2016)
Where things stand	Concentrations still rising	Most chemicals phased out; layer recovering

Exam traps

Ozone depletion is not the cause of global warming, and the ozone hole does not let heat in. The two are separate problems in separate layers; they meet only because some chemicals (CFCs, HFCs) affect both.
Nitrogen and oxygen make up about 99 per cent of dry air but are not greenhouse gases. Water vapour is the largest natural contributor, yet it responds to temperature rather than being directly emitted in amounts that matter.
Carbon dioxide has the lowest global warming potential (1, by definition) but causes the most warming, because so much of it is emitted and it lasts so long. Sulphur hexafluoride has the highest GWP among the common gases.
Methane's GWP is higher over 20 years (about 84) than over 100 years (about 28), because it breaks down in about twelve years. A question that reverses this is wrong.
HFCs do not harm the ozone layer. They were brought under the Montreal Protocol by the Kigali Amendment because they warm the climate, and Kigali is a phase-down of about 80–85 per cent, not a phase-out.
India's HFC freeze year is 2028, with an 85 per cent cut by 2047. The 2024 freeze applies to China and most other developing countries.
The Antarctic ozone hole is deepest in the southern spring, September–October, not in midwinter darkness: it needs both the winter's polar stratospheric clouds and the returning sunlight.
The Montreal Protocol (1987) sits under the Vienna Convention (1985), not under the UNFCCC. In 2009 these two became the first treaties ratified by every country.

Recap

Greenhouse effect: short-wave sunlight in, long-wave heat out; greenhouse gases send part of it back. Natural effect keeps Earth near 15 °C instead of about minus 18 °C.
Main human-added gases: carbon dioxide (fossil fuels, cement, forests), methane (livestock, rice, landfills), nitrous oxide (fertiliser), F-gases (industry). CO2 passed 420 ppm at Mauna Loa in 2023 (NOAA).
Global warming potential compares gases with CO2 = 1 over 100 years: methane about 28, nitrous oxide about 265, SF6 about 23,500 (IPCC AR5).
IPCC AR6 (2021): 2011–2020 about 1.1 °C warmer than 1850–1900; human influence unequivocal; Arctic warming more than twice as fast; feedbacks amplify.
Impacts: sea level up about 0.20 m in 1901–2018, ocean acidification, coral bleaching, glacier retreat, heat and rain extremes; poorest hit hardest.
Ozone layer: stratosphere, about 15–35 km, absorbs UV; ozone hole below 220 Dobson units; ground-level ozone is a pollutant.
Chlorine and bromine from CFCs, halons and others destroy ozone; Antarctic hole opens in September–October.
Vienna Convention 1985, Montreal Protocol 1987 (in force 1989), universal ratification 2009; India joined 1992, ODS Rules 2000; recovery over Antarctica about 2066.
Kigali Amendment 2016 (in force 2019): HFC phase-down; India freezes 2028, 85 per cent cut by 2047; India Cooling Action Plan 2019.

Practice questions

Q1. Among the following gases, which one has the highest global warming potential over a 100-year period?

Carbon dioxide
Methane
Nitrous oxide
Sulphur hexafluoride

Show answer

Answer: D. Sulphur hexafluoride

Sulphur hexafluoride, used in electrical switchgear, has a 100-year GWP of about 23,500 (IPCC AR5). Carbon dioxide is the reference gas at 1, so it is the lowest, not the highest; methane is about 28 and nitrous oxide about 265, both far below SF6.

Q2. Consider the following statements about hydrofluorocarbons (HFCs):
1. They are a major cause of the thinning of the stratospheric ozone layer.
2. Their production and consumption are being phased down under the Kigali Amendment to the Montreal Protocol.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: B. 2 only

Statement 2 is correct: Kigali (2016) brought HFCs under the Montreal Protocol for a phase-down. Statement 1 is wrong: HFCs contain no chlorine or bromine, so they do not deplete ozone; they are controlled because they are powerful greenhouse gases. Options 1 and 3 include the false statement 1; option 4 rejects the true statement 2.

Q3. The ozone hole over Antarctica is usually at its largest during which months?

June–July
September–October
December–January
March–April

Show answer

Answer: B. September–October

The hole opens in the southern spring, September–October, when sunlight returns to the chlorine activated on polar stratospheric clouds during winter. June–July is midwinter darkness, when there is too little sunlight for rapid destruction; by December–January the polar vortex has broken up and ozone-rich air has mixed in; March–April is autumn, before the clouds form.

Q4. Match List I (gas) with List II (a major human source):
List I
A. Methane
B. Nitrous oxide
C. Sulphur hexafluoride
List II
1. Fertilised farm soils
2. Electrical switchgear
3. Livestock and flooded rice fields
Select the correct answer using the code given below:

A-3, B-1, C-2
A-1, B-3, C-2
A-3, B-2, C-1
A-2, B-1, C-3

Show answer

Answer: A. A-3, B-1, C-2

Methane comes from livestock digestion and flooded rice fields (A-3), nitrous oxide mainly from fertilised soils (B-1) and sulphur hexafluoride from electrical switchgear (C-2). Option 2 swaps methane and nitrous oxide; option 3 gives nitrous oxide to switchgear and SF6 to soils; option 4 puts methane with switchgear and SF6 with farms.

Q5. Consider the following statements:
1. Without the natural greenhouse effect, the Earth's average surface temperature would be below the freezing point of water.
2. Nitrogen and oxygen are the most important greenhouse gases because together they make up most of the atmosphere.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: A. 1 only

Statement 1 is correct: without the natural greenhouse effect the average would be roughly minus 18 °C instead of about 15 °C. Statement 2 is wrong: nitrogen and oxygen hardly absorb infrared, so despite their bulk they are not greenhouse gases. Option 2 picks the false statement, option 3 includes it, and option 4 rejects the true statement 1.

Q6. Under the Kigali Amendment to the Montreal Protocol, India is required to freeze its consumption of hydrofluorocarbons in which year?

2019
2024
2028
2047

Show answer

Answer: C. 2028

India is in the group that freezes HFC consumption in 2028, measured against a 2024–2026 baseline. 2019 is when most developed countries began their cuts and when the amendment entered into force; 2024 is the freeze year for China and most developing countries; 2047 is the year by which India must reach an 85 per cent cut, not the freeze.

Q7. Consider the following statements about the Montreal Protocol:
1. It was adopted in 1987 under the Vienna Convention for the Protection of the Ozone Layer.
2. It became, along with the Vienna Convention, one of the first treaties in UN history to be ratified by every country.
3. It is a protocol under the UN Framework Convention on Climate Change.
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: A. 1 and 2 only

Statements 1 and 2 are correct: the Protocol was adopted on 16 September 1987 under the 1985 Vienna Convention, and in 2009 both reached universal ratification. Statement 3 is wrong: the Protocol has nothing to do with the UNFCCC, which dates from 1992. Options 2, 3 and 4 all include the false statement 3.

Q8. Consider the following statements:
1. The global warming potential of methane is higher when calculated over 20 years than over 100 years.
2. Black carbon adds to warming partly by darkening snow and ice and so reducing their albedo.
Which of the statements given above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2

Show answer

Answer: C. Both 1 and 2

Both are correct. Methane lasts only about twelve years, so its effect is concentrated in the first decades: about 84 over 20 years against about 28 over 100 years (IPCC AR5). Black carbon absorbs sunlight in the air and, settling on snow and ice, makes them darker so they reflect less. Options 1 and 2 each drop a true statement, and option 4 rejects both.

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Sources

NASA Earth Observatory and NASA Science: Earth's energy budget, the greenhouse effect and the evidence for climate change (US government) — https://science.nasa.gov/climate-change/
NOAA Global Monitoring Laboratory: trends in atmospheric carbon dioxide, methane and nitrous oxide (Mauna Loa record, annual means to 2024) — https://gml.noaa.gov/ccgg/trends/
IPCC Sixth Assessment Report, Working Group I, Summary for Policymakers (2021); IPCC Fifth Assessment Report, Working Group I, Chapter 8 (2013), global warming potentials — https://www.ipcc.ch/report/ar6/wg1/
Vienna Convention for the Protection of the Ozone Layer (1985); Montreal Protocol on Substances that Deplete the Ozone Layer (1987) and its amendments, including the Kigali Amendment (2016), UNEP Ozone Secretariat — https://ozone.unep.org/treaties
WMO and UNEP, Scientific Assessment of Ozone Depletion: 2022 (released January 2023), executive summary — https://csl.noaa.gov/assessments/ozone/2022/
Ministry of Environment, Forest and Climate Change, Ozone Cell: Ozone Depleting Substances (Regulation and Control) Rules, 2000; India Cooling Action Plan (March 2019); ratification of the Kigali Amendment (2021) — https://ozonecell.nic.in