What is a greenhouse gas?

• A. Gas in the atmosphere that traps heat (carbon dioxide is an example)
• B. Gas that cools the planet
• C. Solid particles that reflect sunlight
• D. Liquid droplets in clouds

Answer: (A)

Greenhouse gases are gases in Earth's atmosphere that trap heat. They absorb infrared radiation emitted by the planet’s surface and re-radiate some of that heat back toward the surface, which warms the lower atmosphere and the surface itself. Carbon dioxide is a common example of a greenhouse gas. These gases are responsible for the warming effect, not cooling, and they are not solid particles that reflect sunlight or liquid droplets in clouds.