In Assignment 8 you will use The Greenhouse Effect simulation originally created by Physics Educational Techonology (PhET). Use any of the three links to access the simulation. The original is from PhET, but we find the openstax version performs better. Just recently PhET created a new prototype, which has not yet been fully tested. If using the original PhET version, click on the "play" button to run it in your web browser.

After starting the simulation, a few options become available at the bottom and at right. For the PhET and openstax version, we recommend keeping "View all photons" un-selected since this will speed up the simulation and allow you to reach an equilibrium temperature more quickly. Also, you can choose your preference of viewing the Earth's surface temperature in Fahrenheit or Celsius. Finally, we recommend that you select "fast" for the simulation speed.

The main feature of this simulation is the ability to adjust the amount of greenhouse gases in the atmosphere and see the effect on Earth's surface temperature. You can choose some preset amounts such as "Today," "Ice Age," "1750," or you can choose another amount using the scroll bar. Other features include adjusting the amount of cloud cover present in the atmosphere, adding fictitious layers of glass in the atmosphere, and discovering how photons of light interact with atmospheric gases.

In the original and openstax versions, what you will see once the simulation begins are yellow and red "photons" moving towards and away from Earth's surface. Photons are small particles of electromagnetic radiation that carry energy. (Physics tells us that we can think of electromagnetic radiation as being composed of either waves or photons.) In this simulation, yellow photons represent radiation from the sun (shortwave radiation) and red photons represent radiation emitted by Earth's atmosphere or surface (longwave radiation). In PhET's new version we see shortwave and longwave radiation represented by waves instead of photons.

Spend some time playing with the simulation before taking the test. Pay attention to how shortwave and longwave radiation interact with the atmosphere and with Earth's surface. One interesting feature you will see in the two older simulations that is not clearly explained is what happens to some photons in the atmosphere. You will see red photons traveling in a certain direction before suddenly changing direction with a small flash. When this happens, it represents a photon being absorbed by the atmosphere and a new photon being emitted in a new direction. After completing the test, we encourage you to play with the other aspects of the simulation to learn more about the greenhouse effect.

NOTE: at the beginning of the simulation, and any time after you have changed the greenhouse gas concentration of the atmosphere, you will need to wait at least a minute or more for the surface temperature to stabilize.