Which statement best describes the role of CO2 in the greenhouse effect?

• A. It cools the surface by blocking sunlight
• B. It traps heat by absorbing infrared radiation
• C. It has no effect on infrared radiation
• D. It primarily reflects visible light away from Earth

Answer: (B)

The main idea is that greenhouse gases trap heat by absorbing infrared radiation, not by blocking sunlight. CO2 is effective at absorbing infrared energy emitted by Earth's surface at specific wavelengths. When CO2 molecules absorb this heat, they warm the surrounding air and re-radiate infrared energy in all directions, including back toward the surface. This slows how quickly heat escapes to space and helps keep the lower atmosphere and surface warmer than they would be otherwise. That’s why increasing CO2 enhances the greenhouse effect.

CO2 doesn’t cool the surface by blocking visible light, and it has a strong effect on infrared radiation, not zero, and it isn’t primarily a reflector of visible light.