In climate assessments, which one of the following greenhouse gases is treated…

Concept

In climate assessments, atmospheric lifetime compares how long an emission-driven increase persists while removal or chemical transformation processes act.

This is not the rapid turnover of individual molecules between reservoirs: carbon dioxide has no single lifetime because an emitted perturbation decays over multiple time scales.

Application

1. Methane is removed mainly by oxidation with hydroxyl radicals in the troposphere. Its atmospheric lifetime is about 12 years.

2. Common chlorofluorocarbons persist for several decades; for example, CFC-11 and CFC-12 have lifetimes of about 50 and 100 years.

3. Nitrous oxide is mainly destroyed after reaching the stratosphere and has an atmospheric lifetime of about 109 years.

4. Carbon dioxide exchanges rapidly among the atmosphere, ocean, and land, but an emission-driven increase has no single short lifetime; part of it persists for centuries or longer.

Contrast and cross-check

• Chlorofluorocarbon: slow stratospheric removal makes representative CFCs multi-decade gases.

• Carbon dioxide: rapid gross exchange does not erase an emission perturbation, whose multi-reservoir response spans long time scales.

• Methane: tropospheric oxidation gives it a roughly decadal lifetime.

• Nitrous oxide: stratospheric loss operates on a roughly century-long time scale.

Result

Therefore, among the listed gases, methane has the shortest atmospheric residence time.