UPSC Prelims 2010 Q149: Environment & Ecology – Climate Change & Greenhouse Gases
Consider the following which can be found in the ambient atmosphere :
1. Soot
2. Sulphur hexafluoride
3. Water vapour
Which of the above contribute to the warming up of the atmosphere ?
- (a) 1 and 2 only
- (b) 3 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Which atmospheric substances contribute to warming
Three substances found in the ambient atmosphere have different roles in trapping heat.
| Substance | Verdict | Reason |
|---|---|---|
| 1. Soot | Correct | Soot (black carbon) absorbs sunlight and contributes to atmospheric warming, both directly and by darkening surfaces like snow/ice |
| 2. Sulphur hexafluoride | Correct | SF6 is one of the most potent greenhouse gases known, with an extremely high global warming potential |
| 3. Water vapour | Correct | Water vapour is actually the most abundant greenhouse gas, trapping significant amounts of heat in the atmosphere |
Atmospheric warming contributors:
| Substance | Role |
|---|---|
| Soot (black carbon) | Absorbs sunlight, warms atmosphere |
| Sulphur hexafluoride | Extremely potent greenhouse gas |
| Water vapour | Most abundant greenhouse gas |
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Substance 3 (water vapour) is also a significant contributor, so '1 and 2 only' is incomplete.
- (b) Incorrect. Substances 1 and 2 (soot, SF6) are also significant contributors, so '3 only' is far too narrow.
- (c) Incorrect. Substance 1 (soot) is also a contributor, so '2 and 3 only' wrongly excludes it.
- (d) CORRECT. All three — soot, sulphur hexafluoride, and water vapour — contribute to atmospheric warming.
Key point
Soot (black carbon), sulphur hexafluoride, AND water vapour all contribute to atmospheric warming — water vapour being the most abundant greenhouse gas, and SF6 being an extremely potent one.
Remember
Soot, sulphur hexafluoride, and water vapour all contribute to atmospheric warming — all three, not a subset.
Common mistakes
- Underestimating water vapour's role as the most abundant greenhouse gas, often overlooked compared to CO2.
- Not knowing sulphur hexafluoride's extremely high warming potential despite its low atmospheric concentration.
- Assuming only 'classic' greenhouse gases (like CO2) matter, missing soot's direct warming contribution.
Exam tip
Beyond CO2: soot (black carbon), SF6, and even plain water vapour all contribute meaningfully to atmospheric warming.
Sources
- Intergovernmental Panel on Climate Change — Climate Change 2007: The Physical Science Basis, Chapter 2 (Changes in Atmospheric Constituents and in Radiative Forcing)
- Intergovernmental Panel on Climate Change — Climate Change 2007: Synthesis Report