What is the greenhouse effect?

• A. The long-term trapping of heat by the ozone layer
• B. The greenhouse effect, a natural process in which heat is retained in the Earth's atmosphere by carbon dioxide, methane, water vapor, and other gases
• C. A cooling of the planet due to reflected sunlight
• D. The loss of heat to space from the upper atmosphere

Answer: (C)

The greenhouse effect is the natural warming of Earth’s surface caused by certain gases in the atmosphere that trap heat. When sunlight reaches Earth, the surface absorbs energy and later emits infrared heat. Greenhouse gases such as carbon dioxide, methane, and water vapor absorb much of that infrared radiation and re-radiate it in all directions, including back toward the surface. This trapping keeps the lower atmosphere warmer than it would be otherwise, creating a stable climate that supports life. It’s not about the ozone layer trapping heat, nor about cooling from reflected sunlight (an albedo effect), and while heat can escape to space, the greenhouse effect specifically describes the warming caused by those atmospheric gases.