Global Equilibrium Energy Balance Interactive Tinker Toy (GEEBITT)
Using a Spreadsheet Climate Model in the High School Classroom
The format of the activity would tie in directly to the hands-on activity being proposed by Robert Kruckeberg and Patrick Cushing. In fact the two activities would probably switch back and forth in the initial phase, with emphasis being placed on the activity appropriate for the grade level of the students being addressed. Robert and Patrick's activity would allow students to model some section of the earth with physical materials. This physical model could then be tested as to its radiative effects - how fast does the temperature change when it is exposed to or removed from an energy source, what is its albedo, and how can these characteristics be adjusted? This physical modeling activity would be based on a section of a world map to which a group of students would be assigned. The students would then have to decide how to divide up their climate box into appropriate amounts of land and water, and then how much ice, vegetation and desert are present in their section.
The ICP Excel Climate Model spreadsheet model activity begins with a similar process with the driving question being: "How can we model the earth's surface?" I envision this activity as taking place with a standard science class (an earth science or a research class) of 34 students or in a workshop situation. Groups of three to four students are assigned sections of the world to model. Instead of working with a box of materials as they do in Robert and Pat's activity, each group is given a set of index cards, color coded to represent different types of surface features. Blue cards for water, white for snow and/or ice, green for vegetation and brown for desert/arid regions. Using a total of ten cards, each group is asked to breakdown their section of the world into the appropriate number of card types. This process takes about 20 minutes as there will be much discussion among the students of each group as to what their appropriate values are. At the end of this section a member of each group can describe their card model and defend their group's reasoning. This process will also take approximately 20 minutes.
The second step of the activity asks the question "How does the selection of different surface features affect the temperature of your model?" At this point the instructor may elect to have some discussion on the nature of black bodies and how their temperature is determined (the Boltzman equation). This would depend upon level of the students. The instructor could leave this calculation out, and simply say that there is a way of determing the temperature of an object based on the amount of energy it absorbs. (If actual experiments as proposed by Robert and Patrick are not done, this would be a good place to utilize Sam Borenstein's virtual experiment on radiative properties.) The instructor can then show viewgraphs of the first two pages of the spreadsheet model before sending the groups to the computer (see figures 1 and 2). In the spreadsheet model all the user adjustable variables are highlighted by light gray boxes as is the incoming solar radiation on page 1 (fig. 1). After inputting the appropriate value into this box, the spreadsheet can then calculate the blackbody temperature (in Kelvin, °Fahrenheit or °Celsius) which is displayed under the yellow boxes to the right in Figure 1. The instructor should emphasize that this would be the average temperature of the earth if the earth had no surface features and compare it to the current average value of 15°C.
The students are then instructed to turn to the second page of the spreadsheet in order to investigate the effect of the distribution of surface features they have just selected. On the second page of the spreadsheet (fig. 2), students have more options to input. They enter the number of cards for each type of surface feature (the top row of gray boxes). The spreadsheet then calculates the percent coverage of that feature in the row of colored boxes below the row for number of cards. The last thing that the students enter on this page are the values for the reflectivities (albedos) of these surfaces. These values can either be obtained experimentally using Robert and Patrick's physical model, or derived from the table of values appearing in the green table in the bottom left hand corner of page 2. The resulting surface temperature of the earth appears in the bottom row of numbers on the right hand side of page 2. These values will always be lower than the blackbody value (appearing in the row above these values) since some energy is now being reflected by the planet. The groups can then discuss the differences in temperature they observe between their various model boxes. The relative importance of percent coverage and albedo can also be observed at this point. Students should end this part of the activity wondering why the temperature if the average earth is -1.6°C and not 15°C.