Question

Arrange the following greenhouse gases in decreasing order of their contribution to total global warming.
A. Nitrous oxide
B. Carbon dioxide
C. Chlorofluoro carbon
D. Methane

• A. C, A, B, D
• B. A, C, B, D
• C. A, B, C, D
• D. B, D, A, C

Hint:

Don't confuse Global Warming Potential (GWP) with overall contribution. While a molecule of methane is more potent than a molecule of CO\(_2\), there are far more CO\(_2\) molecules in the atmosphere, making its total effect the largest.

Answer 1

The Correct Option is D

Step 1: Understand "contribution to global warming".
This contribution depends on two factors: the gas's atmospheric concentration and its global warming potential (GWP) per molecule. The overall effect is the product of these factors.

Step 2: Rank the gases by their overall contribution. 1. Carbon Dioxide (CO\(_2\)): Although it has the lowest GWP of the main greenhouse gases (by definition, GWP=1), its atmospheric concentration is vastly higher than the others, making it the largest contributor to modern global warming (typically over 60%). 2. Methane (CH\(_4\)): It has a much higher GWP than CO\(_2\) but a lower concentration. It is the second-largest contributor. 3. Nitrous Oxide (N\(_2\)O): It has a very high GWP and a longer atmospheric lifetime than methane, but its concentration is lower, making it the third-largest contributor. 4. Chlorofluorocarbons (CFCs) and other halocarbons: They have extremely high GWPs but are present in very small concentrations. Their contribution is smaller than the others listed.

Step 3: Form the sequence. The order in decreasing contribution is: B (Carbon dioxide) \(\rightarrow\) D (Methane) \(\rightarrow\) A (Nitrous oxide) \(\rightarrow\) C (Chlorofluorocarbon). The sequence is B, D, A, C.