What are greenhouse gases?

• A. Gases in atmosphere that trap heat
• B. Gases that cool the planet
• C. Only water vapor
• D. Gases in oceans

Answer: (A)

Greenhouse gases are the gases in Earth’s atmosphere that trap heat by absorbing infrared radiation emitted from the surface. This absorption acts like a blanket, keeping the lower atmosphere and surface warmer than they would be otherwise. They include carbon dioxide, methane, nitrous oxide, ozone, and water vapor. The key idea is that these molecules absorb heat energy and re-radiate it, with some of that energy going back toward the surface. They don’t cool the planet, they warm it, and they’re found in the atmosphere—not in the oceans, and not limited to water vapor alone.