Long-wave radiation is trapped in our atmosphere and keeps our planet warm. This is called?

• A. Urban heat island
• B. Natural greenhouse effect
• C. Atmospheric inversion
• D. Radiation balance

Answer: (B)

Heat from the Sun reaches Earth and warms the surface, which then emits long-wave infrared radiation. Greenhouse gases in the atmosphere—like water vapor, carbon dioxide, and methane—absorb much of that infrared radiation. They then radiate heat in all directions, including back toward the surface, which traps warmth in the lower atmosphere and on the surface. This warming effect is the natural greenhouse effect.

Other terms describe different ideas: an urban heat island refers to localized city warming from concrete and emissions; an atmospheric inversion is a layering that traps pollutants and cold air; and radiation balance is the overall energy in versus energy out of the Earth, not the specific heat-trapping process.