Which sequence describes the greenhouse effect process correctly?

• A. The earth absorbs solar radiation; greenhouse gases absorb some outgoing radiation; greenhouse gases emit absorbed radiation, warming the earth.
• B. The earth reflects most solar radiation; greenhouse gases absorb no radiation; The earth cools.
• C. The earth emits high-energy radiation; greenhouse gases block it completely; The earth becomes colder.
• D. The earth absorbs solar radiation; greenhouse gases reflect it back; The earth warms

Answer: (A)

Think of the greenhouse effect as heat-trapping by infrared radiation. The Sun’s energy reaches Earth as visible light and warms the surface. The surface then emits heat as infrared radiation. Greenhouse gases in the atmosphere absorb some of that outgoing infrared energy and re-emit infrared radiation in all directions. A portion of that re-emitted energy travels back toward the surface, adding warmth and keeping the lower atmosphere and surface hotter than they would be otherwise. So the sequence is: Earth absorbs solar radiation; greenhouse gases absorb part of the outgoing infrared energy; they re-emit that energy, warming the Earth.

The other ideas aren’t correct because greenhouse gases don’t mainly reflect solar radiation, and they don’t block all infrared radiation; they absorb infrared and re-emit it rather than simply reflecting or completely stopping heat from escaping.