For today's climate the planetary emission temperature is approximately 255K, while the average surface temperature is approximately 288K! The difference is a result of the our atmosphere.  The warming that results from the atmosphere is referred to as the Greenhouse effect.

A simple climate model demonstrates the effect of the atmosphere on surface temperature. For simplicity, the atmosphere is represented as a uniform shell surrounding the planet.  In this model, the atmosphere does not absorb solar radiation; however, the atmosphere does absorb and emit infrared radiation. As with the first model, we assume energy balance: the absorbed radiation from the sun must balance the outgoing infrared  radiation.   An energy balance must exist at the top-of-atmosphere and at the surface. 

The greenhouse effect is the warming of the planet that results from the radiative properties of the atmosphere. 
Interactive Model
The model requires you to have a Java enabled Web browser. 
Coming soon: the impact of clouds.
  • Why does the surface temperature change with a change in solar output?
  • Explain why changing the planet's albedo modifies the planet's surface temperature.
  • Can the surface temperature be less than the planet's emission temperature?
  • If you increase the solar output, how can you decrease the surface temperature?
  • Why does surface temperature increase with increasing atmospheric infrared emission? 
  • How might clouds impact the surface temperature?

You control three variables of this simple model: the atmospheric infrared emissivity, the planetary albedo, and  the energy output of the Sun.  The atmospheric  emissivity is the ratio of the radiant energy emitted per unit time per unit area by the atmosphere to the energy emitted by an ideal blackbody at the same temperature. As you vary these parameters the emission temperature of the planet and the temperatures of the surface and atmosphere change.  All temperatures are plotted on a graph as a function of altitude. 

Simple Climate Models | Systems | Emission Temperature | Exercise I | Exercise II | Directory of Related Links
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Steve Ackerman