UPSC Prelims 2008 Q20: Environment & Ecology – Climate Change & Greenhouse Gases
Consider the following:
1. Rice fields
2. Coal mining
3. Domestic animals
4. Wetlands
Which of the above are sources of methane, a major greenhouse gas?
- (a) 1 and 4 only
- (b) 2 and 3 only
- (c) 1, 2 and 3 only
- (d) 1, 2, 3 and 4
Answer: (d) 1, 2, 3 and 4
Explanation
Checking four potential sources of methane
Methane, a major greenhouse gas, is produced through several distinct natural and human-influenced processes.
| Source | Verdict | Reason |
|---|---|---|
| 1. Rice fields | Correct | Anaerobic conditions in flooded rice paddies produce methane via bacterial decomposition |
| 2. Coal mining | Correct | Mining operations release trapped methane from coal seams |
| 3. Domestic animals | Correct | Livestock digestion (enteric fermentation) is a significant methane source |
| 4. Wetlands | Correct | Natural wetland decomposition under anaerobic conditions also produces methane |
Methane source facts:
| Point | Detail |
|---|---|
| Human-influenced sources | Rice fields, coal mining, livestock |
| Natural source | Wetlands |
Answer: (d) 1, 2, 3 and 4.
Why each option is right or wrong
- (a) Incorrect. Sources 2 and 3 (coal mining, domestic animals) are also methane sources, so '1 and 4 only' is too narrow.
- (b) Incorrect. Sources 1 and 4 (rice fields, wetlands) are also methane sources, so '2 and 3 only' is incomplete.
- (c) Incorrect. Source 4 (wetlands) is also a methane source, so '1, 2 and 3 only' wrongly excludes it.
- (d) CORRECT. All four — rice fields, coal mining, domestic animals, and wetlands — are genuine methane sources.
Key point
Rice fields, coal mining, domestic animals (livestock), AND wetlands are ALL sources of methane, a major greenhouse gas — combining human-influenced and natural pathways.
Remember
Methane sources: rice fields, coal mining, domestic animals, and wetlands — all four.
Common mistakes
- Assuming methane sources are only human-influenced, missing natural wetland decomposition.
- Underestimating coal mining's role in releasing trapped methane.
- Not knowing livestock digestion (enteric fermentation) as a significant methane source.
Exam tip
Methane sources span both human activity (rice, coal, livestock) and nature (wetlands) — when a question lists several plausible sources together, 'all of the above' often fits.
Sources
- Intergovernmental Panel on Climate Change — Climate Change 2007: The Physical Science Basis, Chapter 7 (methane sources)
- Ministry of Environment and Forests, Government of India — India: Greenhouse Gas Emissions 2007