The greenhouse effect causes more heat to be retained in the lower atmosphere due to which process?

• A. Absorption of longwave radiation by greenhouse gases
• B. Absorption of shortwave radiation by greenhouse gases
• C. Reflection of sunlight by clouds
• D. Emission of ultraviolet radiation by the Sun

Answer: (A)

The mechanism behind the greenhouse effect is that greenhouse gases absorb infrared radiation and re-emit it in all directions. When the Earth's surface heats up, it emits heat as longwave (infrared) radiation. Greenhouse gases such as water vapor, carbon dioxide, and methane strongly absorb this infrared energy and then re-radiate it, including back toward the surface and the lower atmosphere. This downward component of infrared radiation traps heat near the surface, warming the lower layers of the atmosphere. Shortwave radiation from the Sun (visible light) largely passes through and isn’t the process that retains heat in the lower atmosphere, and ultraviolet emission from the Sun isn’t the mechanism involved here.