Predicted Questions with Model Answers

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Q1 (5 marks — 50 words): What is the ozone layer? State the causes of its depletion.

Model Answer:

The ozone layer in the stratosphere (15–35 km) absorbs 97–99% of harmful UV-B/UV-C radiation. Depletion is caused by Ozone-Depleting Substances (ODS): (1) CFCs (from refrigerants, aerosols) — one Cl atom destroys 100,000 O₃ molecules through catalytic reactions; (2) Halons (fire extinguishers); (3) Carbon tetrachloride; (4) Nitrous oxide (fertilisers — currently the most significant uncontrolled ODS). The Antarctic Polar Vortex amplifies depletion in spring.

Q2 (5 marks — 50 words): What is the Paris Agreement? State India's commitments under it.

Model Answer:

The Paris Agreement (COP21, December 2015) is a legally binding international climate treaty binding 195+ nations to limit global warming to 1.5°C–2°C above pre-industrial levels through Nationally Determined Contributions (NDCs). India's NDC commitments: (1) Net Zero emissions by 2070; (2) 50% electric power from non-fossil sources by 2030; (3) 45% reduction in GDP emissions intensity by 2030 vs 2005; (4) 500 GW non-fossil capacity by 2030.

Q3 (5 marks — 50 words): Explain the causes and significance of biodiversity loss.

Model Answer:

Earth is experiencing its 6th mass extinction — current extinction rate is 100–1,000× the natural background. Main causes: (1) Habitat destruction (80% of threatened species affected — deforestation, agricultural expansion); (2) Overexploitation (overfishing, poaching); (3) Invasive species; (4) Pollution; (5) Climate change (projected dominant driver by 2050). IUCN Red List (2024): 44,016 of 157,190 assessed species (28%) are threatened. Biodiversity loss endangers ecosystem services worth $125–145 trillion/year.

Q4 (10 marks — 150 words): Discuss the causes and effects of ozone layer depletion and the international measures to address it.

Model Answer:

The ozone layer in the stratosphere (15–35 km altitude, peak at ~23 km) absorbs 97–99% of the Sun's harmful UV-B and UV-C radiation, protecting life on Earth.

Causes of depletion:
Chlorofluorocarbons (CFCs) — from refrigerators, air conditioners, aerosol spray cans — are the primary culprit. After release, they drift slowly to the stratosphere (7–10 years), where UV breaks the C-Cl bond, releasing chlorine radicals (Cl•). One Cl atom destroys 100,000 O₃ molecules through a catalytic cycle: Cl• + O₃ → ClO + O₂; ClO + O → Cl• + O₂. Other ODS: Halons (fire extinguishers), Carbon tetrachloride, and Nitrous oxide (fertilisers — now the most significant uncontrolled ODS as CFCs decline).

The Antarctic Ozone Hole forms each spring (September-October) due to the Polar Vortex (−80°C), which enables Polar Stratospheric Clouds (PSCs) that accelerate chlorine reactions. The 2023 ozone hole peaked at ~26 million km² — nearly the area of North America.

Effects:
Ozone depletion increases UV-B reaching the surface: (a) Human health — skin cancer (especially melanoma — Australia has world's highest rates); cataracts (1.6 million cases/year attributed to UV-B); immune suppression. (b) Marine ecosystem — UV-B penetrates 20 m into clear ocean; damages phytoplankton (50% of Earth's oxygen, base of food chain). (c) Agriculture — soybeans, wheat, and corn show yield reductions.

International Response:
The Montreal Protocol (adopted 16 September 1987) is the most successful international environmental agreement — the only UN treaty with universal ratification (197/197 countries). It scheduled phase-out of CFCs (developed countries by 1996; developing by 2010), Halons (1994), and HCFCs (by 2030 for developing). The Kigali Amendment (2016) extended it to HFCs. ODS production has been reduced by 99%, and the ozone layer is projected to fully recover by 2066 over Antarctica, preventing 2 million skin cancer deaths per year. 16 September is observed as World Ozone Day globally.

Q5 (10 marks — 150 words): Critically examine the causes and consequences of climate change, and evaluate the effectiveness of international agreements in addressing it.

Model Answer:

Climate Change: Causes
The enhanced greenhouse effect — intensified by human activities since industrialisation (~1750) — is driving unprecedented warming. Atmospheric CO₂ has risen from 280 ppm (pre-industrial) to 425 ppm (2024) — a 52% increase. GHG sources: fossil fuels (76%), deforestation (11%), agriculture/livestock (methane, N₂O). The result: global average temperature 1.1°C above pre-industrial levels (WMO 2024); 2023 was the warmest year in 125,000 years (1.45°C above baseline).

Consequences:
(Physical): Sea levels rising 3.7 mm/year; glaciers losing 31 billion tonnes ice/year; Arctic warming 4× global average; 4th global mass coral bleaching (2024). (Ecosystem): Accelerated species extinction; Amazon at risk of dieback tipping point (~25% deforestation → savanna). (Human): 200 million projected climate refugees by 2050 (World Bank); declining crop yields in warming regions; expanding disease vectors; coastal city flooding (Mumbai, Kolkata, Miami, New Orleans).

International Response — Effectiveness:

Progress: Paris Agreement (2015) — first universal climate treaty; NDCs from 195+ nations; India's ambitious NDC (Net Zero 2070, 50% non-fossil power by 2030). Renewable energy growth: global solar and wind capacity tripled 2015–2024. Ozone model (Montreal Protocol) shows environmental agreements can work.

Shortcomings: Current NDCs collectively put world on 2.5–3°C warming track — far short of 1.5°C. Climate finance ($100B/year promise) not met. Loss and Damage fund (COP27, 2022) established but underfunded. Developing nations bear disproportionate impact but bear least historical responsibility (USA emitted 25% of all historical CO₂; entire Africa emitted <4%). Geopolitical tensions (USA withdrawal under Trump, 2017–2021) undermine consensus.

Way forward: More ambitious NDCs; carbon pricing mechanisms; CBAM (Carbon Border Adjustment Mechanism — EU 2026); climate finance scale-up; technology transfer; fossil fuel phase-out.

Q6 (10 marks — 150 words): What is biodiversity? Explain the main threats to biodiversity and the international measures to conserve it.

Model Answer:

Biodiversity — the variety of life at genetic, species, and ecosystem levels — underpins all ecosystem services, food security, medicines, and cultural richness. Earth hosts an estimated 8.7 million species; 157,190 have been IUCN-assessed, of which 44,016 (28%) are threatened. The 6th mass extinction is underway: current extinction rate is 100–1,000× the natural background.

Major Threats:
(1) Habitat destruction (primary cause) — tropical deforestation, wetland draining, agricultural expansion affect 80% of threatened species. Amazon has lost 18–20% of cover; at 25% deforestation, a catastrophic "dieback tipping point" is projected. (2) Overexploitation — 33% of fish stocks overfished; illegal wildlife trade (~$23 billion/year) threatens tigers, elephants, pangolins. India: ~200 elephant deaths/year from poaching and human conflict. (3) Invasive species — responsible for 40% of historical extinctions; Water Hyacinth chokes India's wetlands. (4) Pollution — microplastics, pesticides (DDT — banned; neonicotinoids — current bee crisis), eutrophication (Gulf of Mexico dead zone: 22,700 km²). (5) Climate change — projected dominant driver by 2050; coral bleaching, range shifts, phenological mismatches.

International Measures:

CBD (Convention on Biological Diversity, 1992): 196 parties; three objectives: conservation, sustainable use, equitable benefit-sharing
Nagoya Protocol (2010): Access and Benefit-Sharing for genetic resources — protects indigenous knowledge
Kunming-Montreal Global Biodiversity Framework (GBF, COP15, 2022): "30×30" — protect 30% of land + 30% of ocean by 2030; $200 billion/year biodiversity finance; halt human-induced extinctions by 2030
CITES (1975): Regulates international trade in endangered species (~38,000 species listed)
India: Project Tiger (1973) — tiger census 2022: 3,167; Biological Diversity Act (2002); Wildlife Protection Act (1972)

Conservation effectiveness requires integrating biodiversity into economic decisions — recognising nature's $125–145 trillion annual service value.