 # The Earth-Atmosphere-Sun System and Surface Temperature This exercise uses a simple global energy balance model to calculate the mean global surface temperature. By changing values of parameters which are input to the model, the mean global surface temperature is changed. The initial values, which are found below, are for the current earth-atmosphere-sun system.
The greenhouse effect parameter is the fractional part of the longwave radiation from the surface that is re-radiated back to the surface. A greenhouse effect of .40 means that 40% of the longwave radiation emitted by the earth is re-radiated back to the earth (or 60% leaves the earth/atmosphere system).
Incoming solar radiation is entered with no decimal places and has an allowable range of 1 to 3000. Albedo can be entered with 1, 2, or 3 decimal places and has an allowable range of .01 to .90. Greenhouse effect can be entered with 0, 1, 2, or 3 decimal places and has an allowable range of 0 to .999.

Use the calculator below to answer all questions. The "Recalculate" button will recalculate the surface temperature for new values in the other fields. The "Return to initial values" button will return all 4 fields to their initial (i.e. current) values.

1. Does the mean global surface temperature increase or decrease with an decrease in

1. Greenhouse effect
2. Incoming solar radiation at the top of the atmosphere
3. Albedo
(9 points)

2. Suppose the earth was moved farther from the sun, so that in its new orbit it received only 65% of the present amount of incoming radiation. If the albedo and composition of the atmosphere remained as they are now, how much warmer or colder than present would the earth's surface be? (10 points)

3. Suppose the earth was in its current orbit with its current albedo, but it had a thin atmosphere like Mars with a greenhouse effect of .086. How much warmer or colder than present would the earth's surface be? (10 points)

4. For each of the three parameters, calculate the increase or decrease in mean global temperature for an increase of 5% of the initial value of that parameter with the other two parameters held at their initial values. List the three increases or decreases. For the increase of 5% which parameter produces the largest change in mean global temperature? (16 points)

5. If the earth's atmosphere were completely transparent to longwave radiation, what would the mean global temperature be, if incoming solar radiation and albedo remained at initial values? What does that tell you about the magnitude of the surface temperature increase due to the greenhouse effect? (10 points)

6. For Mars, incoming solar radiation = 590 W/m2, albedo = .22, and greenhouse effect = .086. What is the mean surface temperature of Mars? What are the reasons for the difference between the surface temperature of Mars and the surface temperature of Earth? (12 points)

7. For Venus, incoming solar radiation = 2614 W/m2, albedo = .75, and greenhouse effect = .990. What is the mean surface temperature of Venus? What are the reasons for the difference between the surface temperature of Venus and the surface temperature of Earth? (12 points)

8. In its current orbit and with its current albedo, what would the value of greenhouse effect need to be for Venus to have a mean temperature as close as possible to earth's mean temperature? (10 points)

9. What conclusions can you draw from questions 1 through 8? (10 points)

 Incoming solar radiation at top of atmosphere (W/m2) Albedo Greenhouse effect Mean global surface temperature (K)