The Greenhouse Gas Lab
Read and discuss the background information before proceeding to the lab. One person
reads out loud while others follow along silently. Then trade roles so that everyone has a
chance to read.
Background Information
(Adapted from www.explainingclimatechange.ca)
In the Photon Blaster Activity, you learned how gas molecules in our atmosphere interact with different
wavelengths of energy. We know that after absorbing infrared radiation, molecular bonds stretch and bend.
Ultimately, the molecule moves more. Now, we need to look at how this leads to an increase in temperature.
The gases in our atmosphere are most dense (closely packed together) in the troposphere, the layer of the
atmosphere that is closest to Earth. The troposphere is the region where greenhouse gas concentrations are
highest. Infrared radiation that is emitted from the Earth can be absorbed by greenhouse gases in the
troposphere.
When any molecule absorbs energy it becomes excited and moves faster. This increase in movement can
result in a higher temperature. The main difference between air molecules at -15°C and 35°C is their energy.
Temperature is defined by the average kinetic energy (the energy of motion) of the molecules within a
substance.
Recall that air is 78% nitrogen (N2) and 21% oxygen (O2). On a hot day, air feels hot because these molecules
have more kinetic energy than on a cold day. However, neither N2 nor O2 molecules can absorb infrared
radiation because they have evenly distributed charges. How, then, do they gain energy on a hot day?
Although N2 and O2 cannot absorb infrared radiation, they can interact with greenhouse gas molecules such as
carbon dioxide (CO2) and water (H2O). N2 and O2 molecules gain energy when they collide with excited
greenhouse gas molecules. This process of gaining energy is conduction.
Let’s break this down.
A greenhouse gas, such as CO2 absorbs the infrared radiation that is emitted by the Earth (recall that the Earth
is absorbing visible radiation and emitting infrared radiation). Just like the Earth as a whole, any object must
be in radiative equilibrium. Energy in must = energy out.
There are two ways that CO2 can lose the energy it has absorbed:
1) It can re-emit a photon in a random direction. The photon it emits is an infrared photon.
2) The molecule can collide with another molecule, such as oxygen or nitrogen, causing the other
molecule to gain kinetic energy (move faster). This will lead to atmospheric heating.
Stop and discuss in your group , write your explanations down in journal
1. How does a greenhouse gas ‘heat-up’?
2. How does a non-greenhouse gas ‘heat-up’?
The atmosphere is Earth’s way of keeping and using some of the solar energy. Without the gases in our
atmosphere the Earth would be a cold, lifeless planet. The greenhouse process is normal and necessary for a
functioning planet – without all those gases in the atmosphere the Earth wouldn’t be able to hold the heat
energy.
Activity: Greenhouse Effect Computer Simulation
Instructions on getting to the computer simulation
1. Go to this website:
http://phet.colorado.edu/en/simulation/greenhouse
2. “Run” the simulation. This will open the simulation on your computer.
3. This is the same program we used for the Photon Blaster Activity. There are 3 tabs on the top of the
program. Today we’ll use the: “Greenhouse Effect” Tab
4. Notice that there is a Greenhouse Gas Concentration scale on the right side of the screen. You will be
moving the adjuster as you work through this worksheet.
As a group, read these questions together, discuss and then answer the questions in your lab
journal. We are not collecting this work AND you are responsible for knowing the concepts.
1. As the sunlight photon reaches the Earth's surface, what happens? Why does this happen?
2. Why is it that once Earth's surface absorbs sunlight photons, infrared photons are emitted from Earth's
surface? In your answer, include details about the difference in wavelengths between sunlight photons
and infrared photons.
3. Why do some of the infrared photons ‘bounce around’ when they are travelling back through the
atmosphere? What did they hit?
Make this data table:
Atmosphere
during….
Observations
CO2 concentration
CH4 concentration
N20 concentration
Temperature
None
Ice Age
1750
Today
Future
Instructions for data collection:
1. Press the Reset All button on the bottom right of the simulator. Hit “yes” to confirm you want to reset
all settings.
2. On the left, under Greenhouse Gas Concentration, there is a scale. Move the adjuster all the way to
None. This shows you what the temperature on Earth would be if there were NO greenhouse gases in
the atmosphere.
a. Observe what is happening to the photons. Write this description in your data table
b. Wait 3 minutes before observing the temperature. Record this data in your table as well.
c. Discuss and answer the following question in your lab journal:
i. Would life exist on Earth if there were no greenhouse gases in the atmosphere? Why
or why not.
3. Now move the adjuster to the Ice Age setting. Observe the temperature and record this in your lab
journal:
a. Observe what is happening to the photons. Write this description in your data table.
b. Record the concentrations of CO2, CH4, and N2O in your data table.
c. Wait 3 minutes before observing the temperature. Record this data in your table as well.
4. Move the adjustor to the 1750 (this is the year 1750 – just before the industrial revolution and the
beginning of when humans started burning a lot of fossil fuels) setting and record the same
information as Step 3
5. Move the adjustor to the TODAY setting and record the same information as Step 3
6. Move the adjustor to the LOTS setting and record the information. You will not be able to record the
concentrations of greenhouse gases.
7. Make a graph showing the relationship between the concentration of CO2 and temperature. You will
have 4 data points for your concentration of CO2.
Analysis Questions for both labs
As a group, read these questions together, discuss and then answer the questions in your lab
journal.
1. What is the relationship between amount of greenhouse gases in the atmosphere and the
temperature? Use evidence from both the computer simulation with CO2 and the class demo
(Atmosphere in a jar) in your answer.
2. Why do you see this relationship? In your answer, include details about how greenhouse gas
molecules interact with infrared photons and the effect on temperature that results due to this
interaction.
3. Why are greenhouse gases necessary to heat the planet?
4. What happens when “lots” of greenhouse gases are added to the atmosphere?
5. Why does this happen? In your answer, include details about how greenhouse gas molecules interact
with infrared photons and the effect on temperature that results due to this interaction.
6. In the lab today, you saw that both CO2 and H2O are greenhouse gases. How will the water cycle be
affected by an increase in the average global temperature?
7. Why do the solutions to global climate change often discuss CO2 and not H2O?