The capacity of certain gases in the atmosphere to trap heat, thereby warming the Earth, is called the

• A. Ozone layer
• B. Global warming
• C. Greenhouse effect
• D. Heat retention

Answer: (C)

The idea being tested is how certain gases in the atmosphere trap heat and warm the Earth. Sunlight reaches the surface and heats it, then the surface radiates heat (infrared) back toward space. Greenhouse gases—like water vapor, carbon dioxide, methane, nitrous oxide, and ozone—absorb much of this infrared radiation and re-emit it in all directions, including back down to the surface. That trapping of heat keeps the lower atmosphere and surface warmer than they would be otherwise, which is the greenhouse effect. The ozone layer mainly blocks harmful UV radiation, not this infrared heat-trapping process. Global warming refers to the overall rise in Earth’s average temperature, largely driven by this enhanced greenhouse effect, while heat retention is not the specific technical term for the mechanism.