Model of Earth's Energy Balance

Before You Start 

Using this Global Energy Balance Model, we are going to first look at Earth's Surface Temperature under current radiative equilibrium conditions (this means that radiation leaving Earth is balanced by the sun's radiation reaching Earth).  (Remember, incoming radiation will cause Earth to warm up.  The radiation Earth emits will be based on its temperature, as described by the Radiation Laws.  When incoming energy is balanced by outgoing energy, Earth's surface temperature will be constant.)

Then we are going to "perturb" (or change) the radiative equilibrium conditions by modifying one of the factors listed below in the Earth/Sun energy system.  As Earth warms or cools in response to changes in the energy it receives, it will emit radiation  in accordance with its "new" temperature (remember the Radiation Laws!), which will, in turn, affect the Earth/Sun energy system until a new radiative balance and corresponding equilibrium temperature are achieved.  These are the factors we will look at: 

1. Earth's albedo
2. the amount of water vapor in the atmosphere
3. the amount of CO2 in the atmosphere
4. the solar intensity (solar constant)

You can find a list of model input and output parameters here. (Note that we are limiting our exploration to the parameters listed above.)

There are two ways you can go about completing this "lab".  One choice is to work your way through the rest of this page, completing the five "goals" below.  It will give you step-by-step instructions on how to proceed.  The second is to just jump right in and start exploring the Global Energy Balance Model for yourself with the goal of answering these Questions. 

Be sure to record all of your work in your eFolio, no matter which approach you take! 

 

Goal 1: Radiative Equilibrium

Without changing any input parameters, run the Global Energy Balance Model for a 50 year simulation to make sure that the model is in radiative equilibrium for the initial input values.  Record the control run equilibrium surface temperature (and units) for later reference.

T_surf = ___________________

This is the actual average surface temperature of Earth.  What is it in ⁰C?  How about ⁰F?

Goal 2: Earth's Albedo 

Tell Us Your Prediction:  Will the surface temperature increase or decrease as the surface reflectivity (albedo) increases? (You are not penalized in any way for incorrect predictions so give it your best shot.) Note your prediction in your eFolio.

Test Your Prediction:  Run the model to test what happens to the surface temperature when you increase or decrease surface albedo by 10%.  The equilibrium surface temperature change is the Final surface temperature after the 50 year simulation minus the control run equilibrium surface temperature and is given in the output box labeled DT in units of Kelvin (or degrees Celsius since a change of 1.0 K = 1.0 degree C. See for yourself!).  (D stands for the Greek letter "delta" and is used to mean "change" in mathematics.)

Parameter	Change from    to	Equilibrium surface Temp. Change (DT (K))
Surface Albedo	1.0 to 1.1
Surface Albedo	1.0 to 0.90

So what did you learn?  Include your answers in eFolio.

1. Does T_surface increase or decrease as the surface reflectivity is increased?
2. Was this in agreement with your prediction?
3. Does T_surface increase or decrease as the surface reflectivity is decreased?
4. Why does the initial incoming solar radiation absorbed at the TOA (top of atmosphere) decrease when the surface reflectivity is increased?  (Rerun the model and see for yourself.  Look at the top of the output table for the initial TOA solar radiation absorbed.)
   
5. Give an example of how Earth's surface albedo might change.
6. Which statement below is most accurate:

        (a) As the surface albedo increases less infrared radiation is trapped by the model planet so the surface temperature drops.

        (b) As the surface albedo increases more infrared radiation is released by the model planet so the surface temperature drops.

        (c) As the surface albedo increases less solar radiation is absorbed by the model planet so the surface temperature drops.

        (d) As the surface albedo increases more solar radiation is absorbed by the model planet so the surface temperature drops.

Click [Reset] to return base run.            

Goal 3: Atmospheric Water Vapor

Tell Us Your Prediction:  Will the surface temperature increase or decrease as the amount of atmospheric water vapor increases?  Note your prediction in your eFolio.

Test Your Prediction: Perform the experiment below to test your prediction.

Parameter	Change from    to	Equilibrium surface Temp. Change (DT (K))
Atmospheric Water Vapor	1.0 to 1.2
Atmospheric Water Vapor	1.0 to 0.80

So what did you learn?  Include your answers in your eFolio.

1. Where does water vapor in the atmosphere come from (primarily)?
2. Does the surface temperature increase or decrease as the amount of atmospheric water vapor increases?
3. Was this in agreement with your prediction?
4. Look at what happens to the initial value of the TOA outgoing IR (infra-red radiation) between the base run and these two runs.  Why does it decrease from the base run when atmospheric water vapor is increased and increase from the base run when atmospheric water vapor is decreased?
5. Which statement below is most accurate?

            (a)  As atmospheric water vapor increases, less infrared radiation is trapped by the model planet so the surface temperature decreases.

            (b)  As atmospheric water vapor increases, more infrared radiation is trapped by the model planet so the surface temperature decreases.

            (c)  As atmospheric water vapor increases, more infrared radiation is trapped by the model planet so the surface temperature increases.

            (d)  As atmospheric water vapor increases, less infrared radiation is trapped by the model planet so the surface temperature increases.

[Reset] to base run.

Goal 4: Atmospheric CO₂ Concentration

Tell Us Your Prediction:  Will the surface temperature increase or decrease as the concentration of CO₂ increases?  Record your prediction in your eFolio.

Test Your Prediction: Perform the experiment below to test your prediction.

Parameter	Change from    to	Equilibrium surface Temp. Change (DT (K))
Atmospheric CO2	320 to 640
Atmospheric CO2	320 to 160

So what did you learn?  Include your answers in your eFolio.

1. Does the surface temperature increase or decrease as the concentration of CO2 increases?
2. Was this in agreement with your prediction?
3. Look at what happens to the initial value of the TOA outgoing IR between the base run and these two runs. Why does it decrease from the base run when atmospheric CO₂ is increased and increase from the base run when atmospheric CO₂ is decreased?
   
4. Do some on-line research and find out how much atmospheric CO₂ is predicted to increase in the future.  Be sure to cite your sources.
5. Which statement below is most accurate?

        (a)  As CO2 increases, more infrared radiation is absorbed by the model planet atmosphere and re-radiated in all directions so the surface temperature decreases.

        (b)  As CO2 increases, less infrared radiation is absorbed by the model planet atmosphere and re-radiated in all directions so the surface temperature increases.

        (c)  As CO2 increases, less infrared radiation is absorbed by the model planet atmosphere and re-radiated in all directions so the surface temperature decreases.

        (d)  As CO2 increases, more infrared radiation is absorbed by the model planet atmosphere and re-radiated in all directions so the surface temperature increases. 

 [Reset] to base run

Goal 5: Solar Constant

Tell Us Your Prediction: Will the surface temperature increase or decrease as the top of atmosphere solar intensity (Solar constant) increases?  Record your prediction in your eFolio.

Test Your Prediction  Perform the experiment below to test your prediction. 

Parameter	Change from    to	Equilibrium surface Temp. Change (DT (K))
Solar Constant	1.0 to 1.01
Solar Constant	1.0 to 0.99

So what did you learn?  Include your answers in your eFolio.

1. Does the surface temperature increase or decrease as the solar constant increases?
2. Was this in agreement with your prediction?
3. Do a little on-line investigation and tell us how constant the solar constant is.