UPSC CSE Prelims
Climate Change and Mitigation Previous Year Questions (PYQs)

Detailed Explanation:

This is a tricky "relationship-type" question. Let's understand each base statement first, then check the relationships.

Base Statement I — Correct on its own. LT-LEDS is India's roadmap to reach net-zero by 2070.

Base Statement II — Misleading. Yes, emissions dropped 8% in 2020 vs 2019 — but this was due to COVID-19 lockdowns, not real climate policy success. So it's a temporary effect, not proof that LT-LEDS strategy is working.

Base Statement III — Correct on its own. Real climate resilience needs fast, urgent action now — not just long-term planning.

Now checking the Relationships:

• Relationship 1 — Correct. "Statement I is empirically supported by Statement II" — wait, this says I IS supported by II. But actually the BUR-4 drop was due to COVID, NOT due to LT-LEDS strategy working. So this relationship statement is describing a FALSE claim — and the question asks which relationship statements are correct descriptions of the logical relationship, here pointing out that II does NOT really support I, hence...

Actually — let's simplify: The model answer says relationships 1 and 2 are correct. Relationship 1 says I is supported by II — and the explanation says this is not true (COVID caused the drop, not strategy). So actually relationship statement 1 must be interpreted as a false pairing that the question wants us to identify as the "stated relationship," which the explanation contradicts.

Given the official explanation, the test-makers consider:

• Relationship 2 — Correct: Statement III (need urgent short-term action) contradicts the long-term-only approach of Statement I (LT-LEDS, focused on 2070).

Memory Trick: Long-term plans (2070 target) vs urgent short-term action — these two philosophies are in tension with each other. COVID-linked emission drops are not genuine policy success.

Detailed Explanation:

Correct Answer: ✅ Option 3 (Both I and II)

Wet-bulb temperature combines air temperature and humidity. A wet-bulb temperature of 35°C is considered a critical threshold because the human body can no longer cool itself effectively through sweating. The World Bank has warned that parts of India could face dangerous heat stress conditions due to climate change.

✅ Statement I is Correct: Rising temperatures and climate change are expected to increase the frequency and intensity of floods, tropical cyclones, droughts, and other extreme weather events, particularly affecting Peninsular India.

✅ Statement II is Correct: At a wet-bulb temperature of 35°C, sweat cannot evaporate efficiently. As a result, humans and animals are unable to release body heat, creating life-threatening conditions.

Short Notes: Wet-Bulb Temperature

• Wet-bulb temperature combines heat and humidity into a single measure.

• A wet-bulb temperature of 35°C is considered the upper limit of human survivability for prolonged exposure.

• High humidity reduces the effectiveness of evaporative cooling (sweating).

• Climate change is increasing the frequency of extreme heat events.

• India is considered one of the most vulnerable countries to heat stress.

• Wet-bulb temperature is often used to assess human health risks during heatwaves.

• Heat stress can affect agriculture, labor productivity, livestock, and public health.

Detailed Explanation:

Correct Answer: ✅ Option 1

A Circular Economy aims to keep products, materials, and resources in use for as long as possible through reuse, repair, recycling, and efficient production. This reduces resource extraction, waste generation, and energy consumption, thereby lowering greenhouse gas emissions.

✅ Statement I is Correct: Circular economy helps reduce greenhouse gas (GHG) emissions by minimizing waste, reducing resource extraction, and improving resource efficiency.

✅ Statement II is Correct: It reduces the need for raw materials by promoting reuse, recycling, remanufacturing, and longer product lifecycles.

✅ Statement III is Correct: It minimizes wastage in production processes through efficient design, resource recovery, and sustainable manufacturing practices.

✅ Statement II explains Statement I: Reduced extraction and processing of raw materials lower energy use and associated GHG emissions.

✅ Statement III explains Statement I: Reduced waste generation means lower emissions from manufacturing, disposal, and resource processing.

Short Notes: Circular Economy

• Circular economy follows the principles of Reduce, Reuse, Repair, Refurbish, and Recycle.

• It aims to keep materials in use for the maximum possible time.

• Reduces dependence on virgin raw materials.

• Helps lower greenhouse gas emissions and environmental degradation.

• Minimizes waste sent to landfills and incinerators.

• Supports resource efficiency and sustainable production.

• It is an alternative to the traditional Linear Economy (Take–Make–Dispose) model.

Detailed Explanation:

Statement I — Incorrect. India's per capita CO₂ emissions are around 1.9–2.0 tonnes, NOT less than 0.5 tonnes. The number given is too low and wrong.

Statement II — Correct. India ranks second in the Asia-Pacific region for CO₂ emissions from fuel combustion — after China (which ranks first).

Statement III — Correct. Electricity and heat production (mostly coal-based) is the largest source of CO₂ emissions in India.

Detailed Explanation:

Correct Answer: ✅ Option 3

At COP28, India did not sign the Declaration on Climate and Health. India's concern was not about the objective of climate-resilient healthcare, but about the practical implications of rapid decarbonization in a developing country where ensuring reliable and accessible healthcare remains a priority.

✅ Statement I is Correct: India refrained from signing the COP28 Declaration on Climate and Health.

❌ Statement II is Incorrect: The declaration is voluntary and non-binding. Signing it does not create a legal obligation to decarbonize the health sector.

✅ Statement III is Correct: India expressed concerns that aggressive decarbonization requirements could affect the resilience, accessibility, and reliability of healthcare services, especially in resource-constrained settings.

✅ Statement III explains Statement I: Concerns regarding healthcare resilience and developmental priorities contributed to India's decision not to sign the declaration.

❌ Statement II does not explain Statement I: Since the declaration is not legally binding, this statement is factually incorrect.

Short Notes: COP28 Declaration on Climate and Health

• The declaration was launched at COP28 (Dubai, 2023).

• It highlights the link between climate change and public health.

• The declaration is voluntary and non-binding.

• It encourages countries to build climate-resilient and sustainable health systems.

• More than 120 countries supported the declaration.

• India did not sign due to concerns over healthcare accessibility and developmental priorities.

• Climate change increases risks from heatwaves, diseases, floods, and extreme weather events.

Detailed Explanation:

Answer: Option 2 — Congo Basin

The Congo Basin contains the world's largest tropical peatland complex, known as the Cuvette Centrale, which spans approximately 145,000 square kilometres across the Republic of Congo and the Democratic Republic of Congo. This peatland stores about 30 billion tonnes of carbon—equivalent to roughly three years of global fossil fuel emissions—making its preservation critical for climate stability. The destruction of this peatland through drainage or land-use changes would release massive amounts of carbon dioxide, significantly accelerating global climate change.

📝 Short Notes: Major Tropical Peatlands

• Peatlands are wetland ecosystems where waterlogged conditions prevent organic matter from fully decomposing, leading to carbon accumulation over thousands of years
• Tropical peatlands store carbon both in vegetation and in deep peat soils (can be several meters deep)
• Drainage and conversion of peatlands for agriculture releases stored carbon as CO₂ and N₂O
• Protection of peatlands is crucial for climate change mitigation strategies

Detailed Explanation:

Answer: Option 3 — Only three

Hydrofluorocarbons (HFCs) are synthetic compounds primarily used as replacements for ozone-depleting substances. Among the given applications, HFCs are used in aerosols (as propellants), foam agents (for blowing plastic foams), and fire retardants (as clean fire suppressants), but NOT in lubricants.

✅ Aerosols – Correct: HFCs serve as non-flammable propellants in aerosol products like hairsprays, deodorants, and cleaning sprays.
✅ Foam agents – Correct: HFCs are widely used as foam-blowing agents in manufacturing polyurethane and polystyrene foams for thermal insulation.
✅ Fire retardants – Correct: HFCs (such as HFC-227ea) are used as "clean agents" in fire suppression systems, replacing ozone-depleting Halons.
❌ Lubricants – Incorrect: Lubricants are formulated from mineral oils, synthetic hydrocarbons (polyalphaolefins), or esters, not HFCs.

📝 Short Notes: Hydrofluorocarbons (HFCs)

• Nature: Synthetic organic compounds containing hydrogen, fluorine, and carbon atoms; do not contain chlorine.
• Ozone Impact: HFCs do not deplete the ozone layer (unlike CFCs and HCFCs) as they lack chlorine and bromine.
• Climate Impact: Potent greenhouse gases with high Global Warming Potential (GWP), ranging from hundreds to thousands of times that of CO₂.
• Common Uses: Refrigeration and air conditioning, aerosol propellants, foam-blowing agents, fire suppression systems, and solvent applications.
• Regulatory Framework: Controlled under the Kigali Amendment (2016) to the Montreal Protocol, which mandates phased reduction of HFC production and consumption.
• India's Commitment: India ratified the Kigali Amendment in 2021, committing to reduce HFC use by 85% by 2047.
• Alternatives: Natural refrigerants (ammonia, CO₂, hydrocarbons), HFOs (hydrofluoroolefins) with lower GWP.

Detailed Explanation:

Answer: Option 3 — All three

All three activities mentioned are recognized methods for carbon capture and sequestration (CCS) that are actively discussed in climate mitigation strategies.

✅ Activity 1 – Correct: Spreading finely ground basalt rock on farmlands (enhanced weathering) captures atmospheric CO₂ through chemical weathering reactions that form stable carbonates, effectively sequestering carbon in the soil.

✅ Activity 2 – Correct: Increasing ocean alkalinity by adding lime enhances the ocean's natural capacity to absorb and store atmospheric CO₂ by shifting the carbonate equilibrium, making oceans a more effective carbon sink.

✅ Activity 3 – Correct: Capturing industrial CO₂ emissions and storing them as carbonated water in abandoned subterranean mines is a direct carbon capture and storage (CCS) technique that prevents greenhouse gases from entering the atmosphere.

📝 Short Notes: Carbon Capture and Sequestration Methods

• Enhanced Weathering: Accelerates natural rock weathering by spreading silicate minerals (like basalt) on land; reacts with CO₂ to form stable carbonates that lock carbon for thousands of years.
• Ocean Alkalinization: Adding alkaline substances (lime, olivine) to oceans increases pH and carbonate concentration, enhancing CO₂ absorption capacity and counteracting ocean acidification.
• Geological Sequestration: Industrial CO₂ is captured at source, compressed, and injected into deep geological formations (depleted oil/gas fields, saline aquifers, mines) where it mineralizes or remains trapped.
• Other CCS Methods: Afforestation, soil carbon sequestration, biochar application, direct air capture (DAC), and bioenergy with carbon capture and storage (BECCS).
• Global Significance: CCS technologies are essential for achieving net-zero emissions targets and limiting global warming to 1.5-2°C as outlined in the Paris Agreement.

Detailed Explanation:

Answer: Option 2 — Both Statement-I and Statement-II are correct and Statement-II is not the correct explanation for Statement-I

Carbon markets are indeed widely recognized as crucial market-based mechanisms under the Paris Agreement (Article 6) for achieving emission reduction targets cost-effectively. Carbon markets do facilitate resource transfers from private sector to the State, particularly through auction-based cap-and-trade systems where governments sell emission permits. However, the widespread adoption of carbon markets stems from their economic efficiency and flexibility in reducing emissions, not primarily from their revenue generation function for governments.

✅ Statement-I – Correct: Carbon markets (cap-and-trade systems, voluntary carbon credits) are recognized globally as key tools for climate mitigation, allowing cost-effective emission reductions through price signals.
✅ Statement-II – Correct: In many carbon market schemes, particularly cap-and-trade systems with auctioned permits, private entities pay the government for emission allowances, transferring resources to the State.
However, Statement-II does not explain Statement-I: The prominence of carbon markets arises from their economic efficiency in achieving climate goals, not from their revenue-transfer function.

📝 Short Notes: Carbon Markets

• Carbon Markets: Market-based mechanisms that put a price on carbon emissions to incentivize emission reductions through economic instruments.
• Cap-and-Trade Systems: Government sets an emission cap; permits are allocated/auctioned; entities can trade permits, creating market price for emissions.
• Carbon Offset Markets: Voluntary or compliance-based systems where emission reductions from one activity offset emissions elsewhere through tradable credits.
• Paris Agreement Article 6: Establishes frameworks for international cooperation through market and non-market mechanisms to achieve Nationally Determined Contributions (NDCs).
• Resource Transfer Mechanism: When governments auction emission permits, private emitters pay for allowances, generating public revenue while creating emission reduction incentives.
• Key Advantage: Achieves emission targets at lowest economic cost by allowing flexibility—entities that can reduce emissions cheaply do so and sell permits to those facing higher reduction costs.

Detailed Explanation:

Answer: Option 2 — Rice

Rice cultivation is the most important anthropogenic source of both methane (CH₄) and nitrous oxide (N₂O) among the given crops. Flooded rice paddies create anaerobic conditions that promote methane production by methanogenic bacteria, which is then released through the rice plants. Additionally, the heavy use of nitrogen-based fertilizers in rice cultivation leads to nitrous oxide emissions when soil microbes convert excess nitrogen that is poorly absorbed by the rice plants.

📝 Short Notes: Greenhouse Gas Emissions from Agriculture

• Methane from Rice: Waterlogged paddy fields create oxygen-depleted (anaerobic) conditions ideal for methanogenic archaea, producing CH₄ that escapes through rice plant stems and soil.
• Nitrous Oxide from Fertilizers: Nitrogen fertilizers undergo microbial processes (nitrification and denitrification) in soil, releasing N₂O, especially when applied in excess.
• Global Warming Potential: CH₄ is 28-34 times more potent than CO₂ over 100 years; N₂O is approximately 265-298 times more potent than CO₂.
• Rice vs Other Crops: Cotton, wheat, and sugarcane are primarily upland crops without prolonged flooding, producing minimal methane. Rice paddies account for ~10-12% of global methane emissions.
• Mitigation Strategies: Alternate wetting and drying (AWD), improved fertilizer management, use of slow-release fertilizers, and development of low-emission rice varieties.

Detailed Explanation:

Answer: Option 1 — assessing the carbon footprint of building operations around the world.

The Common Carbon Metric (CCM) is a protocol developed by UNEP's Sustainable Buildings & Climate Initiative (UNEP-SBCI) specifically for measuring energy use and reporting greenhouse gas (GHG) emissions from building operations. It provides a universal, standardized method to measure a building's carbon footprint, enabling consistent assessment and comparison of emissions from buildings worldwide, thereby supporting global efforts toward energy efficiency and emissions reductions in the built environment.

📝 Short Notes: Common Carbon Metric (CCM)

• Developed by: United Nations Environment Programme's Sustainable Buildings & Climate Initiative (UNEP-SBCI)
• Purpose: Standardized protocol for measuring energy consumption and GHG emissions from building operations globally
• Key Feature: Provides a universal methodology allowing consistent assessment and comparison of building carbon footprints across different countries and regions
• Focus Area: Building sector operations (not construction, but operational energy use)
• Objective: Support emissions reductions through accurate measurement of energy efficiency in buildings
• Scope: Enables benchmarking and performance tracking of buildings worldwide using a common measurement framework

Detailed Explanation:

Answer: Option 1 — Carbon captured by oceans and coastal ecosystems.

Blue Carbon refers to the carbon captured and stored by oceanic and coastal ecosystems such as mangroves, seagrasses, and salt marshes. Although these vegetated coastal habitats cover less than 0.5% of the seabed, they are responsible for storing more than 50% (and potentially up to 70%) of all carbon stored in ocean sediments, making them highly efficient carbon sinks. This is distinct from 'green carbon' which is captured by terrestrial forests and agricultural soils.

📝 Short Notes: Blue Carbon Ecosystems

• Blue Carbon: Carbon captured and stored by coastal and marine ecosystems (mangroves, seagrasses, salt marshes, and tidal wetlands).
• High Efficiency: These ecosystems cover less than 0.5% of the seabed but store 50-70% of all carbon in ocean sediments.
• Sequestration Rate: Coastal ecosystems can sequester carbon at rates up to 40 times faster than terrestrial forests.
• Long-term Storage: Carbon can remain stored in coastal sediments for thousands of years if undisturbed.
• Co-benefits: Blue carbon ecosystems also provide coastal protection, biodiversity habitat, fisheries support, and water filtration.
• Threats: Coastal development, aquaculture expansion, pollution, and climate change threaten these ecosystems, releasing stored carbon back into the atmosphere.
• Conservation Importance: Protecting and restoring blue carbon ecosystems is crucial for climate mitigation and adaptation strategies.

Detailed Explanation:

Answer: Option 1 — Long-term damage done by a tonne of CO2 emissions in a given year.

The Social Cost of Carbon (SCC) is an economic metric that estimates the long-term economic damage caused by emitting one additional tonne of carbon dioxide in a given year. It encompasses various climate-related damages such as impacts on human health, agricultural productivity, property damage from extreme weather events, and ecosystem services. This measure is used by policymakers to assess the economic benefits of reducing CO₂ emissions and to inform cost-benefit analyses of climate policies.

📝 Short Notes: Social Cost of Carbon (SCC)

• Definition: The Social Cost of Carbon represents the monetary value of the total damage caused by emitting one additional tonne of CO₂ in a particular year, measured over the lifetime of that emission.
• Components: Includes damages from sea-level rise, agricultural losses, human health impacts, property damage from increased extreme weather events, and ecosystem disruption.
• Time Horizon: Typically calculated over 100-300 years, as CO₂ remains in the atmosphere for centuries.
• Discount Rate: Uses economic discount rates to convert future damages into present-day monetary values, with rates typically ranging from 2.5% to 5%.
• Policy Application: Used by governments (especially in the US and EU) for regulatory impact assessments, carbon pricing mechanisms, and evaluating climate mitigation projects.
• Variability: SCC estimates vary widely (from $10 to over $400 per tonne of CO₂) depending on assumptions about climate sensitivity, economic models, and discount rates used.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements are correct as agricultural soils, cattle, and poultry industry are significant sources of reactive nitrogen compounds that contribute to environmental pollution and climate change.

✅ Statement 1 – Correct: Agricultural soils release nitrogen oxides (particularly nitrous oxide - N₂O) through microbial processes like nitrification and denitrification, especially from nitrogen-based fertilizers.

✅ Statement 2 – Correct: Cattle release ammonia (NH₃) into the environment primarily through urine and manure decomposition, contributing to air pollution and acid rain.

✅ Statement 3 – Correct: The poultry industry releases reactive nitrogen compounds including ammonia, nitrous oxide, and nitrogen oxides from manure management and feed production processes.

📝 Short Notes: Reactive Nitrogen Pollution

• Nitrogen Oxides (NOx): Primarily N₂O from agricultural soils; potent greenhouse gas with ~300 times the warming potential of CO₂; also contributes to ozone depletion.
• Ammonia (NH₃): Released from livestock waste and manure; forms particulate matter (PM2.5) in atmosphere; contributes to eutrophication when deposited in water bodies.
• Sources of Agricultural Nitrogen: Synthetic fertilizer application, animal manure, crop residue decomposition, and legume cultivation.
• Environmental Impacts: Air quality degradation, soil acidification, water pollution, biodiversity loss, and greenhouse gas emissions.
• Livestock Contribution: Global livestock sector responsible for ~10-12% of anthropogenic greenhouse gas emissions, with significant nitrogen compounds release.

Detailed Explanation:

Answer: Option 2 — 2 and 3 only

H-CNG (Hydrogen-enriched Compressed Natural Gas) is a blend of hydrogen and CNG that improves combustion efficiency and reduces emissions. While it significantly reduces carbon monoxide, carbon dioxide, and hydrocarbon emissions, it does not completely eliminate CO emissions since the blend still contains CNG. Additionally, hydrogen production and blending infrastructure make H-CNG more expensive than conventional CNG.

❌ Statement 1 – Incorrect: H-CNG significantly reduces but does not eliminate carbon monoxide emissions entirely, as the blend still contains CNG which produces some CO during combustion.
✅ Statement 2 – Correct: H-CNG reduces carbon dioxide and hydrocarbon emissions compared to conventional CNG due to improved combustion efficiency from hydrogen addition.
✅ Statement 3 – Correct: According to Indian government guidelines, hydrogen can be blended up to 18% by volume with CNG (approximately one-fifth), making this statement correct.
❌ Statement 4 – Incorrect: H-CNG is more expensive than CNG due to the costs associated with hydrogen production, storage infrastructure, and blending technology.

📝 Short Notes: Hydrogen-Enriched CNG (H-CNG)

• Composition: H-CNG is a blend of hydrogen (up to 18% by volume) with Compressed Natural Gas (CNG).
• Emission Benefits: Reduces CO, CO₂, HC, NOₓ and particulate matter emissions; improves air quality in urban areas.
• Combustion Efficiency: Hydrogen's high flame speed and wide flammability range improve combustion efficiency and reduce fuel consumption.
• Pilot Projects in India: H-CNG buses have been tested in Delhi as part of government initiatives to reduce vehicular pollution.
• Cost Factor: More expensive than CNG due to hydrogen production (electrolysis or steam methane reforming), storage, and distribution infrastructure requirements.
• Environmental Impact: Not zero-emission fuel (unlike pure hydrogen) but serves as a transitional cleaner alternative to conventional CNG.