Which of the following gas has highest contribution in global warming?
- (a)Carbon-di-oxide
- (b)Chlorofluorocarbon
- (c)Nitrous oxide
- (d)Methane
Correct — A, carbon dioxide (CO2). Although CO2 traps less heat per molecule than the other gases listed, it is released in vastly larger amounts (fossil-fuel burning, deforestation) and lingers in the atmosphere for a long time. As a result it accounts for roughly three-quarters of anthropogenic greenhouse-gas emissions and is the single largest contributor to global warming.
- (b)Chlorofluorocarbon — CFCs have a very high warming potential per molecule and also destroy ozone, but they are present in tiny quantities and are being phased out under the Montreal Protocol, so their overall contribution is small.
- (c)Nitrous oxide — N2O is a potent greenhouse gas per unit mass (mainly from fertilizers), but emitted in far smaller amounts than CO2, so its total share is only a few percent.
- (d)Methane — Methane is the second-largest contributor and traps more heat per molecule than CO2, but its total emissions and atmospheric amount are much lower, so CO2 still dominates.
A gas's effect on warming depends on two things: how strongly each molecule traps heat (global-warming potential, GWP) AND how much of it is emitted. CO2 has a low GWP but enormous emission volume and a long lifetime, so it dominates total forcing. CH4, N2O and CFCs have high GWP but small quantities.
The trap: candidates recall that methane or CFCs are 'more powerful' per molecule and pick them. The question asks for the highest overall contribution, which is quantity x potency x lifetime — and there CO2 wins.
- CO2 is about three-quarters of anthropogenic greenhouse-gas emissions (largest share)
- Methane is 2nd; it has higher per-molecule GWP but far lower total emissions
- N2O and fluorinated gases (CFCs/HFCs) are potent but present in small amounts
- Contribution = emission quantity x warming potential x atmospheric lifetime
- Confusing 'highest per-molecule potency' (methane/CFC) with 'highest total contribution' (CO2)
- Assuming CFCs lead because they also deplete ozone
MPPSC/UPSC ask which gas contributes most to warming, or compare GWP of gases; remember CO2 leads by volume, methane by per-molecule strength.
Statement-I: The atmosphere is heated more by incoming solar radiation than by terrestrial radiation. Statement-II: Carbon dioxide and other greenhouse gases in the atmosphere are good absorbers of long wave radiation. Which one of the following is correct?
- (a) Both correct and II explains I
- (b) Both correct but II does not explain I
- (c) I correct, II incorrect
- (d) I is incorrect, but II is correct
Answer(d) Statement-I is incorrect, but Statement-II is correct — CO2 and other greenhouse gases are efficient absorbers of long-wave (terrestrial) radiation.
Same concept — why CO2 is the key greenhouse gas: it absorbs outgoing long-wave radiation and warms the atmosphere.
Consider the following statements: 1. Kyoto Protocol came into force in the year 2005. 2. Kyoto Protocol deals primarily with the depletion of the Ozone layer. 3. Methane as a greenhouse gas is more harmful than carbon dioxide. Which of the statements given above is/are correct?
- (a) 1 and 2
- (b) 1 and 3
- (c) 1 only
- (d) 3 only
Answer(b) 1 and 3 — methane is more harmful per unit mass than CO2, yet CO2's sheer volume makes it the largest overall contributor.
Same trap — per-molecule potency (methane higher) versus total contribution (CO2 highest).
- practice — not a real PYQ
Although methane traps more heat per molecule, carbon dioxide contributes most to global warming mainly because:
- (a)It is emitted in far larger quantities and persists long in the atmosphere
- (b)It is heavier than air
- (c)It destroys the ozone layer
- (d)It is produced only by volcanoes
Answer(a) Its huge emission volume and long lifetime outweigh its lower per-molecule potency.
- practice — not a real PYQ
Which international agreement was framed to phase out ozone-depleting chlorofluorocarbons (CFCs)?
- (a)Kyoto Protocol
- (b)Montreal Protocol
- (c)Paris Agreement
- (d)Ramsar Convention
Answer(b) Montreal Protocol (1987).