Global Warming and Greenhouse Effect

Global Warming and Greenhouse Effect (UPSC Prelims + Mains)

Think about an Indian summer afternoon: the fan feels useless, the AC runs nonstop, electricity bills rise, and cities record extreme heat. A big reason behind this rising heat trend is global warming, which is strongly linked to the enhanced greenhouse effect. UPSC often asks the basic science (Prelims) and the policy + impacts + solutions (Mains).

1) Start with the Basics: What exactly is happening?

UPSC trap to avoid: Greenhouse effect is not "bad" by default. Without the natural greenhouse effect, Earth would be too cold for most life. The problem is the extra trapping of heat due to human-added gases.

2) Earth's Energy Balance (The Simple Science UPSC Loves)

Earth gets energy from the Sun mainly as short-wave radiation (sunlight). Earth then releases energy back to space as long-wave radiation (heat/infrared).

• Some sunlight is reflected back by clouds, ice, and bright surfaces (this reflection ability is called albedo).
• The rest is absorbed by land and oceans, warming the surface.
• The warm surface emits heat (infrared radiation).
• Greenhouse gases absorb and re-emit part of this outgoing heat, keeping the lower atmosphere warmer.

Why this matters: If ice melts, Earth reflects less sunlight and absorbs more heat, causing further warming (a feedback loop).

3) Mechanism of the Greenhouse Effect (Step-by-step)

1. Sunlight enters the atmosphere and warms Earth's surface.
2. The surface releases heat as infrared radiation.
3. Greenhouse gases absorb some of this infrared radiation.
4. They re-emit heat in all directions—some goes to space, and some returns to the surface.
5. This returning heat raises surface and lower-atmosphere temperature.

Natural vs enhanced: Natural greenhouse effect is like a light blanket. Human activities are adding thickness to the blanket, trapping more heat than before.

4) Greenhouse Gases (GHGs): Who traps heat and why?

Not all gases trap heat. The major gases in air like nitrogen and oxygen do not strongly absorb infrared radiation. Greenhouse gases have molecular structures that can absorb infrared heat.

Major Greenhouse Gases and Key Points

Prelims angle: Methane is stronger than CO2 per unit, but CO2 is the main driver because we emit it in huge amounts and it stays longer.

5) Human Activities Causing the Enhanced Greenhouse Effect

(A) Energy and Industry

• Fossil fuels (coal, oil, gas) in power plants, factories, vehicles → major CO2 emissions.
• Cement production releases CO2 during chemical processing (not only due to energy use).
• Industrial gases (HFCs etc.) from cooling systems and manufacturing.

(B) Land Use Change and Deforestation

• Forests act as carbon sinks (they absorb CO2).
• Deforestation does two harms: it releases stored carbon and also reduces future absorption.
• In India, protecting and expanding forests, mangroves, and soil carbon are important mitigation tools.

(C) Agriculture and Waste

• Methane from cattle (enteric fermentation), rice paddies, and landfills.
• Nitrous oxide from excessive nitrogen fertilizer use and agricultural soils.
• Burning crop residue and biomass can add CO2 and black carbon (short-lived warming pollutant).

6) Feedback Loops: Why warming can accelerate

• Water vapour feedback: Warmer air holds more moisture; water vapour is a GHG; this increases warming.
• Ice–albedo feedback: Melting ice reduces reflectivity; more heat absorbed; more melting.
• Permafrost carbon risk: Thawing can release methane and CO2, adding to warming.
• Ocean feedback: Warmer oceans absorb less CO2 and expand, contributing to sea level rise.

UPSC tip: In Mains, mentioning 2–3 feedbacks shows strong conceptual clarity.

7) Evidence of Global Warming (What we observe)

Global signals

• Rising average temperatures (more frequent record-hot years).
• Warming oceans and increased ocean heat content.
• Sea level rise due to thermal expansion and melting ice.
• Retreating glaciers and shrinking snow cover.
• More intense heatwaves and shifting rainfall patterns in many regions.

Indian signals (good for UPSC answers)

• Heatwaves: Increasing frequency and intensity in many parts of India, affecting health and productivity.
• Monsoon variability: More irregular rainfall—long dry spells followed by intense rain events causing floods.
• Himalayan region: Glacier retreat affects long-term water security and raises risk of glacial lake outburst floods (GLOFs).
• Coastal risk: Sea level rise threatens low-lying coastal areas and deltas (e.g., Sundarbans) and worsens cyclone impacts.
• Oceans around India: Warmer seas can strengthen cyclones and contribute to coral bleaching events.

8) Impacts of Global Warming (UPSC Mains Core)

(A) Water and Agriculture

• Changes in rainfall timing can hurt sowing and harvesting cycles.
• Higher temperature increases evaporation and water stress.
• Heat stress can reduce yields of crops like wheat in sensitive growth stages.
• More pest attacks and plant diseases in warmer conditions.

(B) Disasters and Extreme Events

• Heatwaves become deadlier, especially for outdoor workers.
• Intense rainfall increases urban flooding (poor drainage, concretisation worsen it).
• Stronger cyclones can occur due to warmer ocean surfaces, increasing coastal damage.
• Droughts can intensify in some regions due to higher evaporation and poor rainfall distribution.

(C) Health

• Heatstroke, dehydration, and cardiovascular stress rise during heatwaves.
• Expansion of vector-borne diseases (like malaria/dengue risk zones shifting) in some areas.
• Air pollution interactions: warming can worsen ground-level ozone formation.

(D) Ecosystems and Biodiversity

• Species shift to cooler areas or higher altitudes; many cannot adapt fast enough.
• Coral bleaching becomes more frequent with marine heat stress.
• Forest fires may increase in hotter, drier conditions.

(E) Economy, Migration, and Inequality

• Loss of work hours due to extreme heat affects labour productivity.
• Climate shocks push vulnerable groups into deeper poverty (climate justice issue).
• Coastal erosion and repeated floods can force relocation (climate-induced displacement).

9) Greenhouse Effect vs Ozone Hole (Very common Prelims confusion)

• Greenhouse effect warms Earth by trapping infrared heat (CO2, CH4, N2O etc.).
• Ozone layer depletion happens mainly due to ozone-depleting substances (like older CFCs) that destroy stratospheric ozone, allowing more harmful UV radiation to reach Earth.
• They are related only in limited ways: some gases affect both, but they are not the same phenomenon.

10) Global Efforts and Agreements (UPSC must-know)

11) India's Approach (High-scoring Mains points)

(A) Mitigation actions (reducing emissions)

• Scaling up renewable energy (solar, wind), improving grid and storage.
• Energy efficiency in industry, buildings, appliances (less energy, same output).
• Cleaner transport: public transport, railways, EVs where suitable, fuel efficiency.
• Greening industrial processes and reducing methane leaks.
• Increasing carbon sinks through forests, mangroves, and better soil management.

(B) Adaptation actions (reducing damage)

• Heat Action Plans for cities and districts: early warnings, water points, changing work hours.
• Climate-resilient agriculture: drought-tolerant varieties, micro-irrigation, crop diversification.
• Better flood management: wetland protection, urban drainage upgrades, floodplain zoning.
• Coastal protection: mangrove conservation, cyclone shelters, resilient infrastructure.

(C) Climate justice angle (very important for GS Paper III and Essay)

• India highlights low per-capita emissions and development needs.
• Demand for climate finance and technology transfer from developed countries.
• Focus on livelihoods: farmers, fishermen, urban poor are most affected though they contribute least.

12) Key Terms for Prelims Revision

13) How to Write a Strong UPSC Mains Answer (Ready Framework)

Use this structure:

• Intro: Define greenhouse effect and link it to enhanced warming.
• Body Part 1: Explain mechanism + key gases + human sources.
• Body Part 2: Impacts (global + India examples) + 1–2 feedback loops.
• Body Part 3: Solutions: mitigation + adaptation + policy frameworks.
• Conclusion: Sustainable development + climate justice + way forward.

Mini 150–180 word model conclusion idea: India must grow while cutting emissions intensity through clean energy, efficiency, and nature-based solutions. At the same time, adaptation is urgent because heatwaves, floods, and coastal risks are already affecting lives. Global cooperation must follow equity and CBDR-RC, with finance and technology support to developing countries. A balanced approach can protect livelihoods, biodiversity, and economic stability.

14) UPSC PYQ Themes (Paraphrased) with Answer Pointers

15) Practice MCQs (UPSC Prelims Style) with Answers and Explanations

1. Which of the following statements is/are correct?

   

   1. The greenhouse effect is entirely a human-made phenomenon.
   2. The enhanced greenhouse effect is linked to human activities.

   (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2

   Answer: (b)
   Explanation: Greenhouse effect is natural; the enhanced greenhouse effect is due to additional GHGs from human activities.

2. Which gas is best described as mainly a feedback (not a primary human-emitted driver) in global warming?

   (a) CO2 (b) CH4 (c) Water vapour (d) N2O

   Answer: (c)
   Explanation: Water vapour responds to warming (warmer air holds more moisture), amplifying warming as a feedback.

3. Consider the following pairs:

   1. Kyoto Protocol (1997) — Binding targets mainly for developed countries
   2. Paris Agreement (2015) — Nationally Determined Contributions (NDCs) for all countries

   Which of the above pairs is/are correctly matched?

   (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2

   Answer: (c)
   Explanation: Kyoto focused on developed countries; Paris uses NDCs by all parties.

4. Which of the following increases Earth's albedo the most?

   (a) Expansion of dark ocean surface (b) Expansion of snow/ice cover (c) Deforestation in a humid region (d) Urbanisation with asphalt roads

   Answer: (b)
   Explanation: Snow/ice reflect more sunlight, raising albedo.

5. Tropospheric ozone is best described as:

   (a) Only beneficial and protective (b) Only an ozone-layer component (c) A greenhouse gas and an air pollutant (d) A gas that cools Earth strongly

   

   Answer: (c)
   Explanation: Ground-level ozone harms health and crops and also contributes to warming.

6. Which one of the following contributes to sea level rise even without additional water from melting ice?

   (a) Ocean acidification (b) Thermal expansion (c) El Niño (d) Ozone depletion

   Answer: (b)
   Explanation: Warming water expands, raising sea level.

7. Which of the following is the best reason why CO2 is the biggest driver of human-caused global warming?

   (a) CO2 has the highest GWP among all gases
   (b) CO2 is emitted in huge amounts and a portion stays very long
   (c) CO2 is mainly produced by volcanoes
   (d) CO2 does not have any natural sinks

   Answer: (b)
   Explanation: CO2's volume and long persistence make it dominant even though some gases have higher GWP per unit.

8. HFCs are mainly associated with:

   (a) Fertiliser manufacturing (b) Cooling and refrigeration (c) Rice cultivation (d) Forest fires

   Answer: (b)
   Explanation: HFCs are used in refrigeration/air-conditioning as replacement gases but have high warming potential.

9. Which statement best distinguishes global warming from climate change?

   (a) Global warming includes ozone depletion; climate change does not
   (b) Global warming is temperature rise; climate change includes broader long-term shifts like rainfall and extremes
   (c) Global warming is natural; climate change is human-made
   (d) They are exactly the same term

   Answer: (b)
   Explanation: Global warming is the warming trend; climate change includes many related changes.

10. Which of the following is a correct example of adaptation?

    (a) Switching from coal to solar power
    (b) Afforestation to absorb CO2
    (c) Building heat action plans and early warning systems for heatwaves
    (d) Improving fuel efficiency standards to cut emissions

    Answer: (c)
    Explanation: Adaptation reduces damage from impacts; (a), (b), (d) are mitigation.

16) Quick 10-Line Revision (Last-minute Prelims Notes)

• Greenhouse effect is natural; enhanced greenhouse effect is human-amplified.
• Sun's energy enters as short-wave; Earth releases heat as long-wave (infrared).
• GHGs absorb infrared and re-emit heat, warming lower atmosphere.
• Main GHG drivers: CO2 (fossil fuels/deforestation), CH4 (agriculture/waste), N2O (fertilizers).
• Water vapour is mainly a feedback, not the primary human driver.
• Ice–albedo feedback can accelerate warming.
• Sea level rise: thermal expansion + melting ice.
• Greenhouse effect ≠ ozone hole (different causes and impacts).
• UNFCCC (1992), Kyoto (1997), Paris (2015) are core climate frameworks.
• Mitigation reduces emissions; adaptation reduces harm from impacts.