What is the name of the natural process that warms Earth's lower atmosphere and surface?

• A. The greenhouse effect
• B. The ozone layer process
• C. The albedo feedback
• D. The Milankovitch cycles

Answer: (A)

The natural warming of Earth's lower atmosphere and surface is due to the greenhouse effect. Sunlight reaches Earth and heats the surface, which then emits infrared heat. Greenhouse gases in the atmosphere—water vapor, carbon dioxide, methane, nitrous oxide, and ozone—absorb much of that infrared radiation and re-radiate it in all directions, including back toward the surface. That trapping of heat keeps the lower atmosphere and surface warmer than they would be otherwise, creating a stable warmth that supports life. This is a natural process, though human activities have increased the effect by raising greenhouse gas concentrations.

Other terms refer to different ideas: the ozone layer process involves absorbing ultraviolet radiation, not trapping infrared heat at the surface; albedo feedback concerns how reflectivity (like from ice) alters how much solar energy is absorbed, which can influence warming but isn’t the heat-trapping mechanism itself; Milankovitch cycles are long-term changes in Earth’s orbit and tilt that modulate climate over tens of thousands of years, not the gas-absorption warming.