Week 7 Materials

Day 1

• Setup week 7 notes
• Return quiz3 from Friday. Remember to do retakes early and often! Grades will be available after school
• Finish the blackbody radiation simulation lab
• Start the greenhouse gases simulation lab

Greenhouse Gases Simulation:

Here is a link to the document template for pasting into your notes.

Background

Light can be thought of as little packets of energy called photons. Photons interact with some molecules and not others depending on the wavelength of the light.

Procedure:

Open the PhET simulation link for The Greenhouse Effect.

http://phet.colorado.edu/en/simulation/greenhouse

When the program is open, click on the Photon Absorption tab.

Explore all of the controls in the simulation. Click on different things and figure out what each one does.

Write a brief summary of what the simulation does and shows.

Select the Visible Light option and move the slider to the middle to fire visible light photons at a carbon dioxide molecule (\(CO_2\) ). What happens to the photons?

Try the other molecules listed. What happens to the photons? What direction do they travel after passing the molecules?

The atmosphere is said to be transparent to visible light. Explain what this means in terms of the simulations done so far.

Select the IR option (for infrared), and move the slider to the middle to fire infrared photons at a carbon dioxide molecule.

What happens to the molecule?

What happens to the photon?

What direction do the photons travel after interacting with the molecules?

What does this have to do with global warming?

Fire about 30 infrared photons at each of the molecules in the table below, recording what you see.

Molecules that absorb and reradiate infrared photons are called greenhouse gases.

What behavior indicates that a molecule is a greenhouse gas?

Now, build an atmosphere of 15 molecules each of just \(O_2\) and \(N_2\) , These two molecules comprise most of the atmosphere. Watch what happens when you fire IR photons. Build an atmosphere of just \(CH_4\) , \(H_2O\), and \(CO_2\) . Watch what happens when you fire IR photons.

How are the greenhouse gas and non-greenhouse gas atmospheres different?

Day 2

1. Finish greenhouse gases lab

Day 3

NetLogo climate simulation.

Download NetLogo from https://ccl.northwestern.edu/netlogo/5.3.1/

Open NetLogo and click on File/Models Library. Search for “climate” then click on the “Climate Change” item.

Explore

• This will open up a simple simulation of the earth. Click on the info tab and read through the sections on “what is it?”, “how it works” and “how to use it”. Use the default sun brightness of 1.0 but change the albedo to 0.3. Run the model.
• How is sunlight shown in the model?
• How is heating of the earth represented in the model?
• What happens to the sunlight that hits the earth?
• Let the simulation run for a while. Eventually the simulated earth starts to give off infrared photons. This is actually an inaccuracy in the program. The earth should give off photons immediately after sunlight begins to hit the planet and warm it up.
• If you let the simulation run for a while the temperature eventually levels off. The stable temperature is what is known as the equilibrium temperature or the temperature at which absorbed sunlight is balanced by emitted infrared radiation. What is the equilibrium temperature with no CO2 in the atmosphere?
• Remember, the temperature reflects the number of red dots in the earth. When the temperature is constant, there are about as many incoming yellow arrowheads as outgoing red ones. Why?
• If you were talking to a friend about what you observe in the simulation, how would you explain what is happening with the energy from the sun and the energy from the Earth?

Skeptics

• Some skeptics of global warming say that the temperature of the planet has recently been controlled by the sun’s brightness. The sun’s brightness does vary due to sunspots. Make a graph that supports their point of view. (Hint: you can vary the brightness of the sun in the model – what effect does that have on temperature?) Your graph should include at least 5 data points.
• In making the graph, what is your manipulated variable? What is your responding variable? What are the control variables?
• Could the skeptics be right that changes in the brightness of the sun might account for climate change? Explain.

Ice ages

• The albedo of the planet can change. In the big ice ages much of the earth was covered in snow and ice. What effect would this have on the albedo? Make a graph that shows the effect that changing albedo would have on the earth’s temperature.
• Again the graph should have at least 5 data points.
• In making the graph, what is your manipulated variable? What is your responding variable? What are the control variables?
• How would an increase in snow and ice affect the earth’s temperature during an ice age?
• If the planet warms up, we expect snow and ice to melt. What impact would that have on the global temperature?

Global Warming

• Set \(CO_2\) to 100 molecules. Describe what happens to the infrared photons when you add \(CO_2\).
• Proponents of climate change say that the amount of CO2 (currently 400 parts per million) in the atmosphere has a direct impact on the temperature of the planet. Make a graph that supports their point of view. Include at least 5 data points.
• In making the graph, what is your manipulated variable? What is your responding variable? What are the control variables?
• Explain in words how the plot supports the point of view of the proponents of climate change.

Day 4

Quiz on blackbody radiation and greenhouse gases.