medium · GMAT Verbal

Passage: The greenhouse effect is driven by the ability of certain gases to absorb and re-emit infrared radiation. When solar radiation reaches Earth, it is absorbed by the surface and re-emitted as longer-wave infrared radiation. Greenhouse gases like carbon dioxide and methane have molecular structures that allow them to vibrate in response to these specific infrared frequencies, capturing the energy before it escapes into space. This energy is then re-radiated in all directions, including back toward the surface, resulting in warming. The effectiveness of a greenhouse gas is determined by its Global Warming Potential (GWP), which depends on its ability to absorb radiation and its atmospheric lifetime. Methane, for instance, has a much higher GWP than carbon dioxide over a 20-year period because it is far more efficient at absorbing infrared radiation. However, because methane is removed from the atmosphere more quickly than carbon dioxide, its relative impact decreases significantly when calculated over a 100-year period. Based on the passage, the atmospheric lifetime of a gas influences its GWP primarily by.

1. Changing the frequency of infrared radiation that the molecule can absorb.
2. Affecting the timeframe over which its cumulative warming impact is calculated.
3. Determining whether the gas reacts with carbon dioxide to produce more methane.
4. Altering the molecular structure of the gas so it becomes less efficient at vibrating.
5. Increasing the initial intensity of the radiation it reflects back toward space.

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