6.4.2 Temperature Balances

Earth (Physics only)

• Sun's Energy:
  • Sun's energy is mostly absorbed by the earth's atmosphere, and some is reflected.
  • The amount of energy re-radiated and absorbed leads to Earth's temperature.

The Greenhouse Effect

• Solar Radiation:
  • 343 Watts per m² from the sun.
  • Some of the solar radiation is reflected by the atmosphere and the Earth's surface.
  • Some of the infrared radiation passes through the atmosphere and out into space.
  • Outgoing solar radiation: 103 Watts per m².
  • Outgoing infrared radiation: 240 Watts per m².
• Absorption:
  • About half the solar radiation is absorbed by the Earth's surface.
  • Radiation is converted to heat energy, causing the emission of longwave (infrared) radiation back into the atmosphere.

• Atmospheric Interaction:
  • Some of the infrared radiation is absorbed and re-emitted by the greenhouse gas molecules.
  • The atmosphere is responsible for keeping the Earth at a constant temperature by absorbing IR radiation from the sun and trapping IR re-radiated from the Earth.