What do greenhouse gases do with the re-radiation emitted by Earth's surface?

• A. They radiate the re-radiation back to space
• B. They absorb the re-radiation
• C. They convert it to visible light
• D. They have no interaction with re-radiation

Answer: (B)

Greenhouse gases act like a blanket for infrared heat. The Earth’s surface radiates infrared energy as it warms. Molecules such as water vapor, carbon dioxide, and methane have vibrational modes that readily absorb those infrared wavelengths. After absorbing that energy, the molecules re-emit infrared radiation in random directions. Because some of this energy is directed back toward the surface, the lower atmosphere and surface end up receiving extra heat. So, the primary interaction with the surface-emitted radiation is absorption, which leads to the warming effect as energy is redistributed and partly sent back downward.