Which specific type of radiation is primarily absorbed and re-emitted by greenhouse gases?

• A. Longwave IR (Infrared) Radiation
• B. Shortwave IR
• C. Visible light
• D. Ultraviolet

Answer: (A)

Greenhouse gases interact with the heat radiated by Earth, not the Sun’s light. After the surface warms, it emits infrared radiation in the longwave part of the spectrum. Greenhouse gases have molecular vibrations that strongly absorb this longwave infrared radiation, and they re-emit it in all directions. A portion of that re-emitted energy travels back toward the surface, trapping heat and raising the lower atmosphere’s temperature. In contrast, visible light from the Sun passes through the atmosphere and warms the surface directly, and ultraviolet is largely absorbed by ozone rather than by greenhouse gases. So the type of radiation most associated with absorption and re-emission by greenhouse gases is longwave infrared radiation.