UPSC CSE Prelims
Environment & Ecology Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements about methane hydrate deposits are correct. Methane hydrates are ice-like structures that trap methane and are vulnerable to release under warming conditions, creating a potential climate feedback loop.

✅ Statement 1 – Correct: Global warming can destabilize methane hydrate deposits in permafrost and ocean sediments, triggering methane release—a potent greenhouse gas that amplifies warming.
✅ Statement 2 – Correct: Large methane hydrate reserves are found in Arctic tundra permafrost and in deep-sea sediments along continental margins.
✅ Statement 3 – Correct: Methane in the atmosphere oxidizes to carbon dioxide through hydroxyl radical reactions after approximately 12 years, though CO₂ persists much longer in the atmosphere.

📝 Short Notes: Methane Hydrates

• Structure: Ice-like crystalline solids where methane molecules are trapped within water molecule cages, stable under high pressure and low temperature.
• Major Locations: Arctic permafrost regions and seafloor sediments on continental margins (300-500m depth), particularly offshore India (Krishna-Godavari basin).
• Climate Risk: Methane is 25-30 times more potent as a greenhouse gas than CO₂ over a 100-year period; release creates positive feedback loop.
• Oxidation Process: Atmospheric methane oxidizes via hydroxyl radicals (OH) to CO₂ with an average lifetime of ~12 years.
• Potential Resource: Estimated global reserves exceed conventional natural gas; India conducted successful extraction trial in 2019.
• Destabilization Triggers: Rising ocean temperatures, pressure changes, and permafrost thawing can release stored methane.

Detailed Explanation:

Answer: Option 1 — 1 only

Among the three statements, only the statement about the Asiatic lion is correct as it is naturally found exclusively in India. The double-humped camel and one-horned rhinoceros have natural ranges extending beyond India's borders.

✅ Statement 1 – Correct: The Asiatic lion (Panthera leo persica) is naturally found only in India, with its entire wild population restricted to Gir National Park and surrounding areas in Gujarat, listed as Endangered on the IUCN Red List.

❌ Statement 2 – Incorrect: The double-humped camel (Bactrian camel) is naturally found across Central Asia, particularly in Mongolia and China; while a population exists in Ladakh's Nubra Valley, its natural range is not exclusive to India.

❌ Statement 3 – Incorrect: The one-horned rhinoceros (Indian rhinoceros) is naturally found in both India (Assam, West Bengal, and Uttar Pradesh) and Nepal, making it a shared natural heritage of both countries.

📝 Short Notes: Endemic and Native Species of India

Detailed Explanation:

Answer: Option 4 — 1, 2, 3 and 4

All four statements are factually correct as they accurately describe the dietary habits and reproductive characteristics of various animal species. Each statement can be verified through well-documented examples from the animal kingdom.

✅ Statement 1 – Correct: Many turtle species like green sea turtles and Galapagos tortoises are herbivores, feeding primarily on plants, leaves, and fruits.
✅ Statement 2 – Correct: Numerous fish species such as surgeonfish, parrotfish, and tangs are herbivorous, feeding on algae and seaweed in marine ecosystems.
✅ Statement 3 – Correct: Some marine mammals like manatees and dugongs (sea cows) are herbivores, feeding exclusively on seagrasses and aquatic vegetation.
✅ Statement 4 – Correct: Several snake species including boas, vipers, and sea snakes are viviparous, giving birth to live young instead of laying eggs.

📝 Short Notes: Biodiversity - Feeding Types and Reproductive Modes

• Herbivory in Marine Ecosystems: Herbivorous species play crucial roles in maintaining ecosystem balance by controlling algal growth and vegetation.
• Viviparity vs Oviparity: While most reptiles are oviparous (egg-laying), viviparity has evolved in several snake families as an adaptation to specific environmental conditions.
• Green Sea Turtle: Adults are almost exclusively herbivorous, feeding on seagrasses and algae, though juveniles may be omnivorous.
• Ecological Importance: Herbivorous fish are essential for coral reef health as they prevent algal overgrowth that can smother corals.

Detailed Explanation:

Answer: Option 1 — They are considered harmful to marine ecosystems.

Microbeads are tiny plastic particles (typically less than 5mm) used in cosmetics and personal care products that are released into water bodies through drainage systems. Marine animals like fish, shellfish, and plankton easily ingest these microbeads due to their small size, which can block their digestive systems leading to starvation or death. Additionally, microbeads absorb pollutants and toxins from water, concentrating them in the food chain and potentially harming larger predators, including humans.

📝 Short Notes: Microbeads and Marine Pollution

• Definition: Microbeads are solid plastic particles measuring less than 5mm in diameter, primarily made of polyethylene or polypropylene.
• Sources: Commonly found in facial scrubs, toothpastes, body washes, and other exfoliating personal care products.
• Environmental Pathway: They pass through wastewater treatment plants (too small to be filtered) and enter rivers, lakes, and oceans.
• Marine Impact: Mistaken for food by marine organisms, causing bioaccumulation in the food chain and physical harm to aquatic life.
• Toxic Absorption: Microbeads act as sponges for persistent organic pollutants (POPs) and heavy metals present in water.
• Global Action: Many countries including USA, UK, Canada, and India have banned or restricted the use of microbeads in cosmetics.
• India's Stand: India banned the manufacture of cosmetics containing microbeads in 2020 to protect marine ecosystems.

Detailed Explanation:

Answer: Option 4 — Reducing global warming

Both cirrus cloud thinning and stratospheric sulphate aerosol injection are proposed geoengineering techniques aimed at mitigating climate change. Cirrus clouds trap infrared radiation similar to greenhouse gases; thinning them would reduce heat retention. Sulphate aerosols in the stratosphere reflect incoming solar radiation back into space, thereby cooling the planet.

📝 Short Notes: Geoengineering Techniques for Climate Mitigation

• Solar Radiation Management (SRM): Techniques like aerosol injection and cloud modification aim to reflect sunlight and reduce heat absorption.
• Carbon Dioxide Removal (CDR): Techniques focus on removing CO₂ from the atmosphere through biological or chemical means.
• Concerns: Geoengineering techniques have potential side effects including disruption of precipitation patterns, ozone depletion, and unknown long-term consequences.
• Governance: International frameworks and ethical considerations are essential before large-scale deployment of geoengineering solutions.

Detailed Explanation:

Answer: Option 3 — The Rules provide for exact and elaborate criteria for the identification of sites for landfills and waste processing facilities.

Simple Explanation:

The Solid Waste Management (SWM) Rules, 2016 were notified by the Ministry of Environment, Forest and Climate Change (MoEFCC) to improve scientific waste management in India.

The Rules contain detailed provisions regarding the selection of sites for sanitary landfills and waste processing facilities, including distance from rivers, highways, habitations, and airports.

❌ Statement A – Incorrect: Waste generators are required to segregate waste into three categories—Biodegradable (wet), Non-biodegradable (dry), and Domestic Hazardous Waste, not five categories.

❌ Statement B – Incorrect: The Rules apply to a much wider range of areas, including urban local bodies, census towns, railways, airports, ports, SEZs, industrial townships, and pilgrimage sites.

✅ Statement C – Correct: Schedule I of the SWM Rules, 2016 provides detailed criteria for identifying suitable landfill and waste processing sites.

❌ Statement D – Incorrect: The Rules do not prohibit movement of waste across districts. In fact, they encourage regional facilities serving multiple local bodies.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

Desert plants have evolved multiple leaf modifications to minimize water loss through transpiration in arid environments. All three modifications mentioned—hard and waxy leaves, tiny leaves, and thorns instead of leaves—serve this purpose effectively.

✅ Statement 1 – Correct: Hard and waxy leaves have a thick cuticle layer and reduced stomata, which significantly limit water evaporation from the leaf surface.
✅ Statement 2 – Correct: Tiny leaves reduce the total surface area exposed to the atmosphere, thereby decreasing the potential for water loss through transpiration.
✅ Statement 3 – Correct: Thorns replacing leaves (as seen in cacti and other xerophytes) eliminate the primary transpiring surface, drastically reducing water loss while providing protection from herbivores.

📝 Short Notes: Xerophytic Adaptations in Desert Plants

• Leaf Modifications: Desert plants (xerophytes) exhibit structural adaptations to conserve water in water-scarce environments.
• Thick Cuticle: A waxy, waterproof coating reduces cuticular transpiration.
• Reduced Leaf Surface: Small or needle-like leaves (e.g., Acacia) minimize the area for water loss.
• Leaf Transformation to Spines: In cacti, leaves are modified into thorns, and photosynthesis occurs in green stems.
• Sunken Stomata: Stomata located in pits or grooves reduce air movement and water vapor loss.
• CAM Photosynthesis: Crassulacean Acid Metabolism allows stomata to open at night, reducing daytime water loss.
• Deep Root Systems: Extensive roots access groundwater, complementing above-ground water conservation strategies.

Detailed Explanation:

Answer: Option 4 — 1 only

The Aral Sea has shrunk immensely due to extensive water diversion for irrigation from its feeder rivers (Amu Darya and Syr Darya) since the 1960s, losing over 75% of its area. The Black Sea, while facing pollution and ecological challenges, has not dried up or shrunk significantly. Lake Baikal experiences natural water level fluctuations but has not undergone severe drying like the Aral Sea.

✅ Statement 1 – Correct: The Aral Sea has shrunk by over 75% since the 1960s due to Soviet-era irrigation projects diverting its feeder rivers.
❌ Statement 2 – Incorrect: The Black Sea faces pollution and oxygen depletion issues but has not experienced significant shrinkage or drying.
❌ Statement 3 – Incorrect: Lake Baikal, the world's deepest freshwater lake, has not dried up or shrunk immensely despite some natural water level variations.

📝 Short Notes: Major Water Bodies Under Environmental Stress

• Aral Sea (Central Asia): Once the world's fourth-largest lake, it has lost ~90% of its volume since 1960 due to Soviet irrigation schemes. This has caused desertification, increased salinity, loss of fisheries, and creation of the Aralkum Desert with toxic dust storms.
• Dead Sea (Middle East): Shrinking at about 1 meter per year due to water diversion from the Jordan River and mineral extraction industries.
• Lake Chad (Africa): Has shrunk by ~90% since the 1960s due to climate change, drought, and irrigation demands from surrounding countries.
• Lake Urmia (Iran): Has lost ~80% of its surface area due to dam construction, agricultural water use, and prolonged drought.
• Lake Baikal (Russia): The world's deepest and oldest freshwater lake, containing ~20% of Earth's unfrozen freshwater. Faces pollution threats but remains stable in size.
• Black Sea: Faces eutrophication, anoxic zones, and pollution but maintains its overall size and water volume.

Detailed Explanation:

Answer: Option 2 — 2 only

The question tests the distinction between NGT (a judicial body) and CPCB (a regulatory body). Only statement 2 correctly describes their respective roles, while statement 1 incorrectly claims CPCB was created by executive order.

❌ Statement 1 – Incorrect: Both NGT and CPCB are statutory bodies established by Acts of Parliament. NGT was established under the National Green Tribunal Act, 2010, while CPCB was constituted under the Water (Prevention and Control of Pollution) Act, 1974. Neither was created by executive order.

✅ Statement 2 – Correct: NGT is a specialized environmental court that provides fast-track justice for environmental disputes and reduces litigation burden on higher courts, whereas CPCB is a regulatory body responsible for monitoring and controlling pollution, including maintaining cleanliness of water bodies and improving air quality.

📝 Short Notes: NGT vs CPCB

Detailed Explanation:

Answer: Option 2 — 2 and 3 only

Heavy sand mining in riverbeds disrupts the natural filtration system and hydrological balance, leading to groundwater pollution and lowering of water tables. It does not decrease salinity; rather, in coastal areas, it can increase salinity through saltwater intrusion.

❌ Statement 1 – Incorrect: Sand mining does not decrease salinity; in coastal/estuarine regions, it actually increases salinity by allowing saltwater intrusion from the sea into the river system.

✅ Statement 2 – Correct: River sand acts as a natural filter; its removal reduces filtration capacity, allowing pollutants, heavy metals, and contaminants to seep into groundwater aquifers.

✅ Statement 3 – Correct: Heavy sand mining causes riverbed incision (deepening), which lowers the base level, causing surrounding groundwater to drain into the deepened channel and significantly lowering the water table in adjacent areas.

📝 Short Notes: Environmental Impacts of Sand Mining

• Riverbed Incision: Excessive sand extraction deepens river channels, destabilizing riverbeds and banks, leading to erosion and infrastructure damage (bridges, pipelines).
• Groundwater Depletion: Lowered riverbeds act as drains, pulling down the surrounding water table and affecting wells and agriculture in riparian zones.
• Loss of Natural Filtration: Sand and gravel layers naturally filter water; their removal compromises water quality and increases groundwater contamination risk.
• Saltwater Intrusion: In coastal areas, sand mining creates depression zones that facilitate inland movement of saline water, contaminating freshwater resources.
• Biodiversity Loss: Sand mining destroys aquatic habitats, spawning grounds for fish, and nesting sites for river fauna like turtles and crocodiles.
• Regulatory Framework: Environment (Protection) Act, 1986, and Ministry of Environment guidelines regulate sand mining; many states have banned riverbed sand mining.

Detailed Explanation:

Answer: Option 2 — It tends to reduce the biodiversity in the area in which it grows.

Prosopis juliflora, commonly known as mesquite, is frequently mentioned in news due to its invasive nature and negative impact on native ecosystems. Originally introduced for afforestation and erosion control, it rapidly spreads and forms dense thickets that outcompete native vegetation, thereby reducing biodiversity. Its aggressive growth pattern disrupts ecological balance and has led to efforts in states like Tamil Nadu to remove it and restore native habitats.

📝 Short Notes: Prosopis juliflora (Mesquite)

• Origin: Native to Central and South America; introduced to Africa, Asia, and Australia for afforestation, erosion control, and fuelwood.
• Common names: Mesquite, Thorn Mimosa, Vilayati Babul, Seemai Karuvelam (Tamil Nadu).
• Invasive characteristics: Rapid growth rate, drought tolerance, prolific seed production, and deep root system allowing survival in harsh conditions.
• Ecological impact: Forms dense thickets that prevent growth of native plants; reduces biodiversity; depletes soil moisture and nutrients; alters habitat structure.
• Current status in India: Declared invasive species in several states; particularly problematic in Tamil Nadu, Gujarat, and Rajasthan; removal and restoration programs underway.
• Uses: Despite invasive nature, used for fuelwood, charcoal, fodder (pods), and timber; pods contain high protein content.

Detailed Explanation:

Answer: Option 2 — 2 only

The Global Alliance for Climate-Smart Agriculture (GACSA) is a voluntary multi-stakeholder platform that does not impose binding obligations on its members. Only statement 2 is correct, while statements 1 and 3 contain factual errors regarding GACSA's origins and India's role.

❌ Statement 1 – Incorrect: GACSA was launched in 2014 at the UN Climate Summit in New York, not at the Paris Climate Summit in 2015.
✅ Statement 2 – Correct: GACSA is a voluntary partnership platform, and membership does not create any legally binding obligations for its members.
❌ Statement 3 – Incorrect: GACSA was launched by the Netherlands, FAO, and other countries at the UN Climate Summit in New York; India was not instrumental in its creation.

📝 Short Notes: Global Alliance for Climate-Smart Agriculture (GACSA)

• Launch: September 2014 at UN Climate Summit, New York
• Initiators: Netherlands, FAO (Food and Agriculture Organization), and other partner countries
• Nature: Voluntary, multi-stakeholder platform with no binding legal obligations
• Objective: Promote Climate-Smart Agriculture (CSA) to enhance food security, adapt to climate change, and reduce greenhouse gas emissions
• Membership: Open to governments, international organizations, civil society, private sector, and research institutions
• Three Pillars of CSA: (1) Sustainably increase agricultural productivity and incomes, (2) Adapt and build resilience to climate change, (3) Reduce greenhouse gas emissions where possible
• India's Position: India has been cautious about GACSA and has not been a founding or leading member; concerns relate to potential impacts on smallholder farmers

Detailed Explanation:

Answer: Option 1 — 1 and 2 only

This question tests knowledge of the Forest Rights Act, 2006, particularly regarding Critical Wildlife Habitats and Habitat Rights for Particularly Vulnerable Tribal Groups (PVTGs). Statement 3 is incorrect because State governments, not the Union Ministry, have the authority to declare Habitat Rights.

✅ Statement 1 – Correct: The Forest Rights Act, 2006 explicitly defines "Critical Wildlife Habitat" as areas within National Parks and Wildlife Sanctuaries that require inviolate conservation for wildlife protection, and can only be declared based on scientific evidence after due process of resettlement.

✅ Statement 2 – Correct: In 2015, the Baiga tribal community in Madhya Pradesh became the first in India to be granted Habitat Rights under the FRA, 2006, allowing them to continue living in the Kanha Tiger Reserve buffer zone with access to forest resources.

❌ Statement 3 – Incorrect: Under the Forest Rights Act, 2006, it is the State governments (not the Union Ministry) that have the authority to declare and vest Habitat Rights for Primitive Tribal Groups after obtaining consent from the concerned communities and establishing resettlement measures.

📝 Short Notes: Forest Rights Act, 2006 — Key Provisions

• Official Title: The Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, 2006
• Critical Wildlife Habitat (CWH): Defined under Section 2(b) as areas within National Parks and Wildlife Sanctuaries that require inviolate conservation for wildlife protection; can be notified only after scientific evidence and completion of resettlement process
• Habitat Rights: Under Section 3(1)(e), Primitive Tribal Groups (now called Particularly Vulnerable Tribal Groups - PVTGs) and pre-agricultural communities are entitled to habitat rights for habitation and livelihood
• Authority: State governments have the power to declare Habitat Rights after obtaining consent from Gram Sabhas and affected communities
• First Grant: Baiga tribe in Madhya Pradesh (2015) was the first PVTG to receive Habitat Rights in Kanha Tiger Reserve buffer zone
• PVTGs in India: 75 tribal groups across 18 states are classified as Particularly Vulnerable Tribal Groups based on criteria like pre-agricultural level of technology, low literacy, and declining population

Detailed Explanation:

Answer: Option 2 — The United Nations Conference on Sustainable Development 2012, Rio de Janeiro

The Partnership for Action on Green Economy (PAGE) was established in response to the United Nations Conference on Sustainable Development (UNCSD) 2012, also known as Rio+20, held in Rio de Janeiro, Brazil. This conference reaffirmed global commitment to sustainable development and emphasized the transition to green economies that promote environmental sustainability, social inclusion, and economic growth. PAGE was launched as a UN collaborative initiative involving UNEP, ILO, UNDP, UNIDO, and UNITAR to support countries in developing policies and strategies for sustainable and inclusive economic growth.

📝 Short Notes: Major UN Conferences on Sustainable Development

• PAGE Partner Agencies: UNEP (lead), ILO, UNDP, UNIDO, UNITAR
• PAGE Objective: Support countries in reframing economic policies and practices around sustainability
• Focus Areas: Green industrial policy, sustainable consumption and production, green fiscal reform, ecosystem services, and inclusive growth

Detailed Explanation:

Answer: Option 1 — Increased plant growth due to increased concentration of carbon dioxide in the atmosphere

Carbon fertilization refers to the phenomenon where elevated atmospheric CO₂ concentrations enhance the rate of photosynthesis in plants, leading to increased plant growth and biomass production. Since CO₂ is a key substrate for photosynthesis, higher concentrations allow plants to synthesize more sugars (glucose), thereby accelerating growth rates. This effect is distinct from global warming (temperature increase), ocean acidification, or adaptive responses to climate change.

📝 Short Notes: Carbon Fertilization and Plant Physiology

• Carbon Fertilization: The enhancement of photosynthetic rates and plant growth due to elevated atmospheric CO₂ levels.
• Photosynthesis Basics: Plants absorb CO₂, water, and sunlight to produce glucose (C₆H₁₂O₆) and release oxygen (O₂) as a byproduct.
• Current CO₂ Levels: Atmospheric CO₂ concentration has reached approximately 420 ppm (as of recent measurements), the highest in millions of years, primarily due to fossil fuel combustion and deforestation.
• Growth Response: Many C3 plants (wheat, rice, soybeans) show significant growth enhancement with increased CO₂, though C4 plants (maize, sugarcane) show less response.
• Limitations: Carbon fertilization benefits are limited by other factors like nutrient availability (nitrogen, phosphorus), water stress, and temperature extremes.
• Ecosystem Impacts: While increased plant growth may sequester more carbon, this effect is offset by increased respiration, decomposition, and other climate change impacts.