After solar energy is absorbed by the Earth's surface, what happens next?

• A. It is re-radiated at a longer wavelength than the absorbed energy
• B. It is stored as chemical energy
• C. It passes through to space immediately
• D. It is converted to kinetic energy and dissipates

Answer: (A)

When sunlight heats the surface, that energy is first stored as heat in the land or water, raising its temperature. A heated object then emits its own radiation. The wavelength of this emitted radiation depends on the object's temperature: cooler temperatures emit in the infrared, while the Sun’s surface (much hotter) emits mainly visible light. So the Earth’s surface, at typical temperatures, radiates energy back to space predominantly as infrared light, at wavelengths longer than the incoming sunlight. This re-radiation is the main way Earth sheds the absorbed energy.

Greenhouse gases in the atmosphere absorb some of that infrared and re-radiate it, which traps heat and keeps surface temperatures higher. While energy is also used to warm air or drive evaporation, the immediate next step after absorption is emission of infrared radiation at longer wavelengths.