GREENHOUSE EFFECT – COMPLETE NOTES

  GREENHOUSE EFFECT – COMPLETE NOTES

🔹 What is Greenhouse Effect?

The Greenhouse Effect is a natural process in which certain gases in Earth’s atmosphere trap heat (infrared radiation), keeping the planet warm enough to support life.

👉 Without it, Earth’s temperature would be about –18°C, instead of current ~15°C

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🔹 How it Works (Mechanism)

1. Sun emits shortwave radiation (UV + visible light)

2. Earth absorbs energy → warms up

3. Earth emits longwave infrared radiation

4. Greenhouse gases absorb & re-radiate heat → warming atmosphere

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🔹 Types of Greenhouse Effect

1. Natural Greenhouse Effect

   • Essential for life

   • Maintains Earth’s temperature

2. Enhanced Greenhouse Effect

   • Due to human activities

   • Causes global warming

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🌿 GREENHOUSE GASES (GHGs)

🔹 Major Greenhouse Gases

Gas	Formula	Source	Importance
Carbon dioxide	CO₂	Fossil fuels, deforestation	Largest contributor
Methane	CH₄	Cattle, rice fields, landfills	25× more potent than CO₂
Nitrous oxide	N₂O	Fertilizers	Long-lasting
Water vapor	H₂O	Evaporation	Most abundant
Ozone	O₃	Secondary pollutant	Both good & bad
Chlorofluorocarbons	CFCs	Refrigerators, AC	Very high GWP

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🔹 Key Exam Facts

CO₂ contributes ~76% of total greenhouse emissions

Methane = most dangerous per molecule
Water vapor = most abundant but not directly controlled by humans
CFCs → ozone depletion + greenhouse effect

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🌡️ GLOBAL WARMING

🔹 Definition

Increase in Earth’s average temperature due to enhanced greenhouse effect.

🔹 Causes

Burning fossil fuels

Deforestation
Industrialization
Agriculture (methane, nitrous oxide)

🔹 Effects

Melting glaciers

Sea level rise
Climate change
Extreme weather events
Loss of biodiversity

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🔹 Important Concepts

🌎 Global Warming Potential (GWP)

Measures heat trapped by gas compared to CO₂

CO₂ = 1 (reference)

Gas	GWP
CO₂	1
CH₄	~25
N₂O	~298
CFCs	Thousands

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🧠 IMPORTANT EXAM POINTS

Greenhouse effect is natural + beneficial

Global warming is harmful (excess effect)
Kyoto Protocol & Paris Agreement aim to reduce emissions
Developed countries historically emit more GHGs
India is a major emitter but low per capita emission

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📘 MCQs (MOST IMPORTANT)

1. Which gas contributes most to global warming?

A. Methane
B. Carbon dioxide
C. Nitrous oxide
D. Ozone

✅ Answer: B

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2. Which gas has highest Global Warming Potential?

A. CO₂
B. CH₄
C. CFCs
D. O₃

✅ Answer: C

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3. Greenhouse effect is caused by:

A. Oxygen
B. Nitrogen
C. Greenhouse gases
D. Dust

✅ Answer: C

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4. Which is not a greenhouse gas?

A. CO₂
B. CH₄
C. O₂
D. N₂O

✅ Answer: C

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5. Methane is mainly produced by:

A. Vehicles
B. Factories
C. Cattle & rice fields
D. Volcanoes

✅ Answer: C

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📘 STATEMENT-BASED QUESTIONS (ADVANCED)

🔹 Question 1

Consider the following statements:

1. Greenhouse effect is always harmful

2. It helps maintain Earth’s temperature

3. It is caused by oxygen

A. 1 only
B. 2 only
C. 1 & 2
D. 2 & 3

✅ Answer: B
👉 Statement 1 ❌, 2 ✔️, 3 ❌

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🔹 Question 2

Consider the following gases:

1. Carbon dioxide

2. Methane

3. Oxygen

4. Nitrous oxide

Which are greenhouse gases?

A. 1, 2, 4
B. 1, 3, 4
C. 2, 3
D. All

✅ Answer: A

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🔹 Question 3 (UPSC Type)

Consider the following statements:

1. Methane has higher heat trapping ability than CO₂

2. Water vapor is the most abundant greenhouse gas

3. Nitrogen is a greenhouse gas

A. 1 & 2
B. 2 & 3
C. 1 & 3
D. All

✅ Answer: A

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🔹 Question 4

Consider the following:

1. CFCs cause ozone depletion

2. CFCs are greenhouse gases

3. CFCs are natural gases

A. 1 & 2
B. 2 & 3
C. 1 & 3
D. All

✅ Answer: A

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🔹 Question 5

Which statements are correct?

1. Global warming is due to enhanced greenhouse effect

2. Greenhouse gases trap infrared radiation

3. Ozone always protects Earth

A. 1 & 2
B. 2 & 3
C. 1 & 3
D. All

✅ Answer: A