Environment: previous-year questions
273 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 80 of them came in the last five papers.
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Why is a plant called *Prosopis juliflora* often mentioned in news ?
Answer (b) & explanation
It reduces biodiversity where it grows (b). Prosopis juliflora, called vilayati babul or vilayati kikar, is a thorny tree from Central and South America. The British brought it to India in the 19th century, and later it was planted widely to green dry lands and give firewood. It spread out of control, forming dense thickets, drawing down groundwater, and releasing chemicals that stop other plants from growing. It now crowds out native grasses and trees, making it a major invasive species. It is not widely used in cosmetics (a) or pesticides (c).
Notice where it hurts most: Gujarat's Banni grasslands in Kachchh, home to Maldhari herders, and Delhi's Ridge, where it is being removed. Tamil Nadu has ordered its clearing too.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Most of the world’s coral reefs are in tropical waters.
- 2. More than one-third of the world’s coral reefs are located in the territories of Australia, Indonesia and Philippines.
- 3. Coral reefs host far more number of animal phyla than those hosted by tropical rainforests.
Which of the statements given above is/are correct ?
Answer (d) & explanation
All three statements are correct (d). Statement 1 is right because reef-building corals need warm (about 20–29°C), clear, shallow, salty water, so most reefs lie in the tropics, between about 30°N and 30°S. Statement 2 is right because Australia, Indonesia and the Philippines together hold more than a third of the world's reef area. Indonesia alone has the most, and the Coral Triangle is the richest region. Statement 3 is right because reefs host more animal phyla (major body plans) than rainforests. Many sea groups, such as echinoderms, never moved onto land.
Notice the threat: the fourth global bleaching event (2023–25) hit over 80% of reefs. India's reefs are in the Gulf of Mannar, Gulf of Kachchh, Lakshadweep and the Andamans.
Answer as per the official UPSC answer key.
“Momentum for Change : Climate Neutral Now” is an initiative launched by
Answer (c) & explanation
The UNFCCC Secretariat launched it (c). Momentum for Change is a UNFCCC programme, started in 2011, that honours practical climate solutions, such as women-led projects and climate finance ideas. Climate Neutral Now, launched in 2015, invites people, companies and governments to measure their emissions, cut them, and offset the rest using UN-certified credits. The IPCC (a) assesses climate science and does not run such schemes. UNEP (b) runs other programmes, and the WMO (d) deals with weather and climate data.
Notice the related Article 6 carbon markets of the Paris Agreement, whose rules were finalised at COP29 (Baku, 2024). India launched its own Carbon Credit Trading Scheme (2023).
Answer as per the official UPSC answer key.
In which one of the following States is Pakhui Wildlife Sanctuary located ?
Answer (a) & explanation
Pakhui is in Arunachal Pradesh (a). Pakhui, also called Pakke, lies in the East Kameng district, in the foothills of the eastern Himalayas. It is bounded by the Kameng and Pakke rivers and joins Nameri National Park in Assam. It became a tiger reserve in 2002. It is famous for its four hornbill species, and its Hornbill Nest Adoption Programme lets local Nyishi villagers earn money by guarding nests, turning former hunters into protectors. The reserve is not in Manipur (b), Meghalaya (c) or Nagaland (d).
Notice the festival: the Pakke Paga Hornbill Festival is Arunachal's first conservation festival. Nagaland's Hornbill Festival at Kisama is a different, cultural event. Arunachal's other tiger reserves are Namdapha and Kamlang.
Answer as per the official UPSC answer key.
How is the National Green Tribunal (NGT) different from the Central Pollution Control Board (CPCB) ?
- 1. The NGT has been established by an Act whereas the CPCB has been created by an executive order of the Government.
- 2. The NGT provides environmental justice and helps reduce the burden of litigation in the higher courts whereas the CPCB promotes cleanliness of streams and wells, and aims to improve the quality of air in the country.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because both bodies are statutory. The CPCB was set up in 1974 under the Water (Prevention and Control of Pollution) Act and was later given powers under the Air Act, 1981 and the Environment Protection Act. The NGT was set up under the NGT Act, 2010. Statement 2 is right because the NGT gives fast environmental justice, deciding cases within six months, and reduces the load on higher courts. The CPCB works to keep streams and wells clean and to improve air quality.
The NGT's principal bench is in New Delhi, with four zonal benches. Notice the principles it applies: sustainable development, the precautionary principle, and polluter pays, under Section 20 of the NGT Act.
"executive order" is the slip. The CPCB came from a law, like the NGT.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. The definition of “Critical Wildlife Habitat” is incorporated in the Forest Rights Act, 2006.
- 2. For the first time in India, Baigas have been given Habitat Rights.
- 3. Union Ministry of Environment, Forest and Climate Change officially decides and declares Habitat Rights for Primitive and Vulnerable Tribal Groups in any part of India.
Which of the statements given above is/are correct ?
Answer (a) & explanation
Statements 1 and 2 are correct (a). Statement 1 is right because the Forest Rights Act, 2006 defines critical wildlife habitat in Section 2(b), as areas that must be kept free of people for conservation, decided after scientific study and consultation. Statement 2 is right because, in 2015–16, the Baiga tribe in Dindori, Madhya Pradesh, became the first community to receive habitat rights. Statement 3 is wrong because these rights are recognised through the gram sabha, sub-divisional and district committees under the Act. The nodal ministry is the Ministry of Tribal Affairs, not the Environment Ministry.
Notice the term: PVTGs number 75, and the PM-JANMAN mission (2023) funds housing, roads and water for them.
Answer as per the official UPSC answer key.
Which of the following has/have shrunk immensely/dried up in the recent past due to human activities ?
- 1. Aral Sea
- 2. Black Sea
- 3. Lake Baikal
Select the correct answer using the code given below :
Answer (a) & explanation
Only the Aral Sea has shrunk drastically (a). From the 1960s, the Soviet Union diverted the Amu Darya and Syr Darya rivers to grow cotton in Uzbekistan and Kazakhstan. The Aral Sea, once the world's fourth-largest lake, shrank by about 90% into small pools. It left behind the salty Aralkum desert and wrecked the fishing towns. The Black Sea (2) faces pollution and low oxygen in its deep water but has not dried up. Lake Baikal (3), the world's deepest lake, faces pollution but is still full.
Kazakhstan's Kok-Aral dam (2005) has partly brought back the North Aral. Notice other lakes shrinking due to people: Lake Chad, Lake Urmia in Iran, and the Dead Sea.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Birds
- 2. Dust blowing
- 3. Rain
- 4. Wind blowing
Which of the above spread plant diseases ?
Answer (d) & explanation
All four spread plant diseases (d). Plant pathogens such as fungi, bacteria and viruses need a way to move from one plant to another. Wind (4) carries fungal spores over long distances; wheat rust spores can travel hundreds of kilometres. Blowing dust (2) carries spores and bacteria stuck to soil particles. Rain (3) splashes spores and bacteria from sick leaves onto healthy ones. Birds (1) carry spores and seeds on their feet, feathers and droppings, and spread parasitic plants such as mistletoe. So options leaving any of them out are wrong.
Insects such as aphids and whiteflies are major carriers of viruses. Notice the threat of wheat blast, which reached Bangladesh in 2016, and the pink bollworm in Bt cotton.
Answer as per the official UPSC answer key.
The term “sixth mass extinction/sixth extinction” is often mentioned in the news in the context of the discussion of
Answer (d) & explanation
Option (d) best describes it. Earth has gone through five mass extinctions. The last, about 66 million years ago, wiped out the dinosaurs after an asteroid struck. Scientists warn that a sixth is under way, this time caused by humans: overuse of resources, habitat loss and fragmentation, pollution, invasive species and climate change. Species are vanishing at many times the natural background rate. Options (a) and (c) name only one cause each: monoculture or GM crops. Option (b) is wrong because the term is not about a coming meteorite.
Notice the IPBES report (2019), which warned that about one million species face extinction. The Kunming–Montreal Framework (2022) responded with the 30x30 target: protect 30% of land and sea by 2030.
Answer as per the official UPSC answer key.
Which of the following statements best describes “carbon fertilization” ?
Answer (a) & explanation
Option (a) describes carbon fertilization. Plants use CO₂ for photosynthesis. When there is more CO₂ in the air, many plants, especially C3 plants such as wheat and rice, photosynthesise faster and grow more, and their stomata lose less water. This is the carbon fertilization effect, and satellites show a greening of the Earth partly because of it. Option (b) is the greenhouse effect or global warming. Option (c) is ocean acidification. Option (d) is not a scientific term.
Notice the limits: the benefit fades when nitrogen or water is short, and studies show crops grown under high CO₂ have less protein, zinc and iron. So more CO₂ is not good news for nutrition. C4 plants such as maize gain much less.
Answer as per the official UPSC answer key.
Which of the following is/are the possible consequence/s of heavy sand mining in riverbeds ?
- 1. Decreased salinity in the river
- 2. Pollution of groundwater
- 3. Lowering of the water-table
Select the correct answer using the code given below :
Answer (b) & explanation
Statements 2 and 3 are correct (b). River sand works like a sponge and a filter. It stores water and cleans it as it seeps down into aquifers. Heavy mining deepens and lowers the riverbed, so water drains away faster and the water table falls (3). Without the sand layer, polluted surface water reaches groundwater without being filtered (2). Statement 1 is wrong because mining does not reduce salinity. Near the coast, a deeper channel lets seawater push further upstream, so salinity rises.
Other harms include eroded banks, weakened bridges and lost habitat for gharials and turtles. Notice the rules: the Sustainable Sand Mining Management Guidelines (2016) and the Enforcement and Monitoring Guidelines (2020) require district surveys and replenishment studies.
"decreased salinity" reverses what actually happens near river mouths.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Climate and Clean Air Coalition (CCAC) to Reduce Short Lived Climate Pollutants is a unique initiative of G20 group of countries.
- 2. The CCAC focuses on methane, black carbon and hydrofluorocarbons.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because the Climate and Clean Air Coalition (CCAC) was started in 2012 by UNEP and six countries: Bangladesh, Canada, Ghana, Mexico, Sweden and the USA. It is not a G20 body. Statement 2 is right because it targets short-lived climate pollutants: methane, black carbon, HFCs and tropospheric ozone. These stay in the air only days to years, so cutting them slows warming quickly and also cleans the air.
India joined the CCAC in 2019. Notice the related efforts: the Global Methane Pledge (COP26, 30% cut by 2030), which India has not signed, and the Kigali Amendment (2016) to phase down HFCs, which India ratified in 2021.
Answer as per the official UPSC answer key.
If you want to see gharials in their natural habitat, which one of the following is the best place to visit ?
Answer (b) & explanation
The Chambal River is the best place to see gharials (b). The National Chambal Sanctuary, set up in 1979 and shared by Madhya Pradesh, Rajasthan and Uttar Pradesh, holds most of the world's wild gharials. The gharial is Critically Endangered, needs clean, fast, sandy rivers, and eats only fish. Bhitarkanika (a) in Odisha is famous for saltwater crocodiles, not gharials. Pulicat (c) is a lagoon known for flamingos. Deepor Beel (d), near Guwahati, is a Ramsar wetland.
Smaller gharial groups live in the Girwa (Katarniaghat), Son and Gandak rivers, and in Corbett. Notice India's three crocodilians: the gharial, the mugger (marsh crocodile) and the saltwater crocodile, all on Schedule I.
Bhitarkanika does have crocodiles, but they are saltwater crocodiles.
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Answer as per the official UPSC answer key.
From the ecological point of view, which one of the following assumes importance in being a good link between the Eastern Ghats and the Western Ghats ?
Answer (a) & explanation
Sathyamangalam links the two Ghats (a). Sathyamangalam Tiger Reserve in Erode district, Tamil Nadu, sits where the Western and Eastern Ghats meet. It joins the Nilgiri Biosphere landscape, including Mudumalai, Bandipur and BRT Hills (Biligiri Rangaswamy Temple), giving tigers and elephants a vital corridor. It was declared a tiger reserve in 2013. The other options are wrong because Nallamala (b), home of the Nagarjunasagar-Srisailam reserve, and Seshachalam (d) lie entirely in the Eastern Ghats, while Nagarhole (c) is entirely in the Western Ghats.
BRT Hills is the other well-known meeting point of the two ranges. Notice the Moyar river gorge, which separates the Nilgiris from the Sathyamangalam forests.
Answer as per the official UPSC answer key.
The term ‘M-STrIPES’ is sometimes seen in the news in the context of
Answer (b) & explanation
M-STrIPES is used to manage tiger reserves (b). M-STrIPES (Monitoring System for Tigers – Intensive Protection and Ecological Status) is a GPS-based mobile app brought in by the NTCA and the Wildlife Institute of India in 2010. Forest guards use it to record patrol routes, wildlife sightings, poaching signs and habitat data, which gives managers a live picture of protection in each reserve. It has nothing to do with captive breeding (a), NavIC (c), or highway security (d).
Data from M-STrIPES feeds into the All India Tiger Estimation, which counted 3,682 tigers in 2022. Notice the related tools: camera traps, the Management Effectiveness Evaluation of reserves, and the CA|TS global standard for tiger sites.
Answer as per the official UPSC answer key.
Consider the following statements in respect of Trade Related Analysis of Fauna and Flora in Commerce (TRAFFIC) :
- 1. TRAFFIC is a bureau under United Nations Environment Programme (UNEP).
- 2. The mission of TRAFFIC is to ensure that trade in wild plants and animals is not a threat to the conservation of nature.
Which of the above statements is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because TRAFFIC was set up in 1976 as a joint programme of WWF and IUCN, not as a bureau under UNEP. It is now an independent NGO based in Cambridge, UK. Statement 2 is right because its mission is to make sure trade in wild plants and animals is not a threat to conservation. It tracks markets and smuggling routes, and supports CITES with data and training.
TRAFFIC India works with WWF-India and helps the Wildlife Crime Control Bureau fight trade in pangolins, star tortoises, red sanders and other species. Notice how often UPSC asks who runs what: TRAFFIC belongs to WWF+IUCN, while CITES's secretariat is run by UNEP.
TRAFFIC works with CITES (hosted by UNEP), but TRAFFIC itself is not part of UNEP.
Answer as per the official UPSC answer key.
In India, if a species of tortoise is declared protected under Schedule I of the Wildlife (Protection) Act, 1972, what does it imply ?
Answer (a) & explanation
Schedule I listing gives the same protection as the tiger (a). Schedule I of the Wildlife (Protection) Act, 1972 gives the highest protection and the heaviest penalties: jail of 3 to 7 years and a fine of at least ₹25,000. Every animal on it gets the same level of protection, whether it is a tiger or a star tortoise. Listing does not mean the animal is extinct in the wild or beyond saving (b). It does not mean it is endemic to one region (c). So (d) is wrong too.
After the 2022 amendment, there are four Schedules: I and II for animals with different levels of protection, III for plants, and IV for CITES species. Notice the protected Indian tortoises, such as the Indian star tortoise and the Travancore tortoise.
Answer as per the official UPSC answer key.
In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation technique ?
- 1. It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature.
- 2. Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms.
- 3. Genetic engineering can be used to create microorganisms specifically designed for bioremediation.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1 and 3 are correct (c). Bioremediation uses microbes, fungi or plants to clean up pollution by speeding up the natural biodegradation that happens anyway (1). Genetic engineering can create microbes designed for particular pollutants (3). Ananda Chakrabarty's oil-eating Pseudomonas was the first patented living organism (1980). Statement 2 is wrong because heavy metals like cadmium and lead cannot be broken down. Microbes and plants can only change their form or concentrate them, as in phytoremediation. So "any ... readily and completely" goes too far.
Bioremediation is used after oil spills, and India's TERI developed Oilzapper for this. Notice the related terms: in-situ (on site) and ex-situ (removed) treatment, and bioaugmentation (adding microbes).
"any", "readily" and "completely" in one line is a strong warning sign.
Answer as per the official UPSC answer key.
Recently there was a proposal to translocate some of the lions from their natural habitat in Gujarat to which one of the following sites ?
Answer (b) & explanation
The proposal was to move lions to Kuno-Palpur (b). Kuno-Palpur in Madhya Pradesh was chosen to give the Asiatic lion a second home, so that a single epidemic or disaster could not wipe out the only wild population in Gir, Gujarat. In 2018, canine distemper killed over 20 Gir lions. In 2013, the Supreme Court ordered the move, but Gujarat has never sent any lions. Corbett (a), Mudumalai (c) and Sariska (d) were not the chosen sites.
In 2022, Kuno National Park instead received cheetahs from Namibia and South Africa under Project Cheetah. The 2025 count found 891 lions in Gujarat. Notice that Gujarat is spreading lions across the Greater Gir landscape, including Barda, as its own alternative.
Answer as per the official UPSC answer key.
Due to some reasons, if there is a huge fall in the population of species of butterflies, what could be its likely consequence/consequences ?
- 1. Pollination of some plants could be adversely affected.
- 2. There could be a drastic increase in the fungal infections of some cultivated plants.
- 3. It could lead to a fall in the population of some species of wasps, spiders and birds.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1 and 3 are correct (c). Butterflies are pollinators of many flowering plants, so a big fall in their numbers could hurt pollination (1). Butterflies and their caterpillars are also food for wasps (some lay eggs in caterpillars), spiders and birds. Losing them would affect these predators further up the food web (3). Statement 2 has no link. Butterflies do not control plant fungi, so their loss would not cause a sudden rise in fungal infections of crops.
Butterflies are also bio-indicators, sensitive to pesticides and climate change. Notice the wider idea of a trophic cascade: losing one link in the food web can ripple through the whole ecosystem, much like declines in bees threaten food security.
Answer as per the official UPSC answer key.