Experiment Procedure:

1. On the simulation screen, select "Greenhouse Effect".
2. Then, select "Reset All", and select "Yes" in the box that pops up.
3. In the Greenhouse Gas Concentration box, move the slider to None. A simulation for an atmosphere with no greenhouse gases will automatically start running.
4. As the simulation runs, document your observations of:

• • the paths of solar radiation photons (incoming energy)
  • the paths of terrestrial (infrared) radiation photons (outgoing energy)
  • the relative number of solar radiation photons compared to terrestrial radiation photons.
  • the change in temperature on the thermometer.

1. Record the temperature once it roughly settles on a value (i.e., when the atmosphere reaches equilibrium). Note that the temperature may continue to fluctuate slightly (1-2 degrees) once equilibrium is reached.
2. Under Atmosphere During... select "Today". A simulation for today's atmosphere will automatically start running.
3. Repeat steps 4 through 6 for today's atmosphere. For your observations, make note of the differences in both the paths and the relative number of each type of photon compared to that observed for the atmosphere with no greenhouse gases. If needed, move the speed adjuster to a slower speed to accurately observe the photons.
4. Record the values for the greenhouse gases - carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) (in parts per million (ppm)), and for water vapor (H2O) (in terms of relative humidity) in today's atmosphere, shown under Greenhouse Gas Composition.

After completing the experiment:

• In the submission template document, for Experiment 1, Observations and Data, document your observations, equilibrium temperature values, and greenhouse gas composition from steps 4, 5, and 8 of the experiment.
• Based on your observations and data from the experiment, formulate a written conclusion that generalizes the interaction between incoming and outgoing radiation with greenhouse gases, and the effect of greenhouse gases on the atmosphere's equilibrium temperature. Enter your conclusion in the submission template document, under Experiment 1, Conclusions.

PhET Simulation (colorado.edu)