Using the standard 100-year time horizon, which one of the following gases has…

Concept

Global Warming Potential compares the heat trapped by one unit mass of a gas with the heat trapped by the same mass of carbon dioxide over a specified time horizon. The 100-year GWP is the standard comparison used in inventories; carbon dioxide is the reference and is assigned a value of 1.

Application

1. Use the same 100-year horizon for every offered gas.

2. Carbon dioxide is the reference gas, so its GWP is 1.

3. Methane has a 100-year GWP of about 27–30, depending on its source classification.

4. Nitrous oxide has a 100-year GWP of about 273, which is greater than the values for methane and carbon dioxide.

5. Carbon monoxide has an assessed indirect GWP100 of about 1.9, far below nitrous oxide at about 273 over the same 100-year horizon.

Cross-check and contrast

• Methane: strong warming per unit mass, but a much shorter atmospheric lifetime than nitrous oxide.

• Nitrous oxide: strong infrared absorption combined with a lifetime of roughly a century produces the largest 100-year value among these options.

• Carbon dioxide: the comparison baseline, not the maximum in this set.

• Carbon monoxide: its assessed indirect GWP100 is about 1.9, far below the value for nitrous oxide.

Therefore, nitrous oxide (N2O) has the highest 100-year GWP among the gases listed.