✅ Answer: D) Chlorofluorocarbons (CFCs)CFCs have the highest GWP — 1,000 to 10,000 times that of CO₂ over 100 years. GWP values: CO₂ = 1 (reference); CH₄ = 25; N₂O = 298; CFCs = 1,000-10,000. Despite lower concentrations, CFCs are extremely potent GHGs. They also destroy the ozone layer. CFCs have been phased out under the Montreal Protocol (1987). HFCs (hydrofluorocarbons) replaced CFCs but are also potent GHGs — being phased out under the Kigali Amendment (2016).

✅ Answer: B) Ozone depletion by phasing out ozone-depleting substancesThe Montreal Protocol (1987) was signed to phase out ozone-depleting substances (ODS), primarily CFCs. It is considered the most successful international environmental treaty. The ozone layer is slowly recovering and is expected to fully recover by 2065. The Kigali Amendment (2016) to the Montreal Protocol also phases out HFCs (which replaced CFCs but are potent GHGs). India ratified the Montreal Protocol in 1992.

✅ Answer: A) Weakening the Southwest monsoon, leading to drought riskEl Niño (warming of the central/eastern Pacific Ocean) typically weakens India’s Southwest monsoon, leading to drought risk. La Niña (cooling of the Pacific) strengthens the monsoon. However, the relationship is not always consistent — the Indian Ocean Dipole (IOD) can counteract El Niño’s effect. A positive IOD can offset El Niño’s negative impact on India’s monsoon. El Niño years: 1982-83, 1997-98, 2015-16, 2023.

✅ Answer: A) Well below 2°C, preferably 1.5°C above pre-industrial levelsThe Paris Agreement (2015, COP21) aims to limit global average temperature rise to well below 2°C above pre-industrial levels, with efforts to limit it to 1.5°C. Each country submits Nationally Determined Contributions (NDCs). India committed to 500 GW renewable energy by 2030 and net zero by 2070. The IPCC’s 1.5°C Special Report (2018) warned of severe consequences if warming exceeds 1.5°C. Current policies put the world on track for ~2.7°C warming.

✅ Answer: A) UNEP and WMO (1988)The IPCC (Intergovernmental Panel on Climate Change) was established in 1988 by UNEP (UN Environment Programme) and WMO (World Meteorological Organization). It assesses scientific literature on climate change and publishes Assessment Reports. IPCC AR6 (2021-22) confirmed that human activities have unequivocally caused global warming. IPCC won the Nobel Peace Prize in 2007 (shared with Al Gore). IPCC does not conduct original research but synthesises existing research.

✅ Answer: A) Elevated ocean temperatures causing corals to expel their symbiotic algae (zooxanthellae)Coral bleaching occurs when elevated ocean temperatures (even 1-2°C above normal) cause corals to expel their symbiotic algae (zooxanthellae), which give corals their colour and 90% of their energy. Without algae, corals turn white (bleach) and can die if stress continues. Ocean acidification (from CO₂ absorption) also weakens coral skeletons. The Great Barrier Reef has experienced mass bleaching events. India’s Lakshadweep and Andaman coral reefs are also threatened.

✅ Answer: C) 2070India committed to achieving net zero emissions by 2070 at COP26 (Glasgow, November 2021). This is later than the 2050 target of developed countries. India’s Panchamrit commitments: 500 GW non-fossil energy by 2030; 50% electricity from renewables by 2030; reduce emissions intensity by 45% by 2030; reduce total projected carbon emissions by 1 billion tonnes by 2030; net zero by 2070. India is the 3rd largest emitter but has low per capita emissions.

✅ Answer: A) AntarcticaThe ozone hole is most severe over Antarctica. It was discovered in 1985 by British scientists. The extreme cold of Antarctic winters creates polar stratospheric clouds (PSCs) that accelerate ozone destruction by CFCs. The ozone hole typically forms in September-October (Antarctic spring) and closes in November-December. There is also some ozone depletion over the Arctic but it is less severe. The ozone layer is slowly recovering due to the Montreal Protocol.

✅ Answer: A) Water vapour (H₂O)Water vapour is the most abundant greenhouse gas in the atmosphere, contributing about 50% of the natural greenhouse effect. However, water vapour is a feedback mechanism, not a forcing — it amplifies warming caused by other GHGs. CO₂ is the most important anthropogenic (human-caused) GHG, contributing ~76% of human-caused warming. CO₂ concentration has risen from 280 ppm (pre-industrial) to over 420 ppm (2023) — the highest in 3 million years.

✅ Answer: B) HFCs (Hydrofluorocarbons)The Kigali Amendment (2016) to the Montreal Protocol aims to phase down HFCs (Hydrofluorocarbons). HFCs were introduced as replacements for CFCs (which destroy ozone) but are potent greenhouse gases (GWP up to 14,800). The Kigali Amendment is expected to prevent 0.5°C of warming by 2100. India ratified the Kigali Amendment in 2021. The original Montreal Protocol phased out CFCs and other ozone-depleting substances. The Kigali Amendment is a climate change measure, not an ozone protection measure.