In the greenhouse effect, greenhouse gases trap which form of radiation emitted by the Earth's surface?

• A. Longwave radiation
• B. Shortwave radiation
• C. Ultraviolet radiation
• D. Visible radiation

Answer: (A)

Greenhouse gases trap infrared radiation. The Earth’s surface heats up from sunlight and emits energy mainly as longwave infrared radiation. Because molecules like water vapor, carbon dioxide, and methane readily absorb infrared wavelengths, they capture this energy and re-emit it in all directions, including back toward the surface. This trapping keeps heat in the lower atmosphere and near the surface. In contrast, shortwave radiation from the Sun is mostly visible light and ultraviolet, which passes through the atmosphere and is not the form that these gases block in the greenhouse effect. Ultraviolet and visible radiation emitted by the Earth are not the primary heat-trapping forms here, since the Earth’s own emission is dominated by infrared wavelengths.