1. Incoming Solar Radiation:
* The Sun emits a wide spectrum of radiation, including visible light, infrared, and ultraviolet.
* About 30% of this radiation is reflected back into space by clouds, ice, and the Earth's surface.
* The remaining 70% is absorbed by the Earth's atmosphere and surface, heating them up.
2. Earth's Re-emission:
* The Earth, now warmed by the absorbed solar radiation, emits its own radiation, primarily in the infrared spectrum (heat).
* This re-emitted radiation is known as terrestrial radiation or longwave radiation.
3. Greenhouse Effect:
* Some of the Earth's re-emitted infrared radiation is trapped by greenhouse gases in the atmosphere (like water vapor, carbon dioxide, methane, and nitrous oxide).
* This trapping of heat is what keeps Earth's average temperature around 15°C (59°F), making it habitable.
* Without the greenhouse effect, Earth's average temperature would be significantly colder, around -18°C (0°F).
4. Radiation Escape:
* Not all of the re-emitted radiation is trapped.
* Some of it escapes directly into space, contributing to Earth's energy balance.
5. Factors Affecting Radiation Escape:
* The amount of greenhouse gases in the atmosphere influences how much infrared radiation escapes.
* Higher levels of greenhouse gases trap more heat, leading to a warming effect.
* Cloud cover can also affect radiation escape, reflecting some outgoing radiation back towards the Earth.
Key Points:
* Earth re-emits the absorbed solar radiation primarily as infrared radiation.
* Greenhouse gases trap some of this re-emitted radiation, warming the planet.
* The balance between incoming and outgoing radiation is crucial for maintaining Earth's temperature and climate.
In Conclusion: Earth re-emits the energy it receives from the Sun as infrared radiation. This radiation is partially trapped by greenhouse gases, creating the greenhouse effect that keeps Earth warm. The rest of the re-emitted radiation escapes into space, maintaining Earth's energy balance.
