The Greenhouse Effect

Our calculation left out the atmosphere, except that we included reflection of sunlight back into space and some of this is from clouds.

The atmosphere can cool the earth if cloud cover increases.

The atmosphere can also warm the earth by absorbing infrared radiation and radiating it back to earth.

Here is an exaggerated example.

• Six units of solar energy come in.
• Twelve units of infrared energy are radiated from the earth's surface.
• The atmosphere absorbs them and radiates
  • Six unite out into space
  • Six units down to the earth's surface.
• Net result for space:
  • Six units of solar energy come in.
  • Six units of infrared energy are radiated back.
• Net result for earth's surface:
  • Twelve units of solar+ infrared energy come in.
  • Twelve units of infrared energy are radiated back.
  • So the Earth's surface will be hotter.

The gasses that do this are called greenhouse gasses

• CO₂ (carbon dioxide).
• CH₄ (methane).
• NO₂ (nitrogen dioxide)
• chlorofluorocarbons. (Also eat ozone.)

With burning coal since the industrial revolution, amount of CO₂ in the atmosphere has increased.

Is the earth getting warmer?

ASTR 121 Home