Modeling the Complexities of the Carbon Cycle Utilizing Excel

This activity is part of the community collection of teaching materials on climate and energy topics.

These materials were created by faculty as part of the CLEAN Climate Workshop, held in May, 2012 and are not yet part of the CLEAN collection of reviewed resources.

Andrea Bixler, Clarke University
Lindsay Dubbs, University of North Carolina, Chapel Hill
Dave Finster, Wittenberg University
Harold Geller, George Mason University
Jeanne Troy, Koshland Science Museum

Topic: Modeling the complexities of the carbon cycle, incorporating both natural and anthropogenic influences and processes.

Course Type: Introductory level courses in climate science, ecology, environmental science


In this set of activities, the instructor introduces the carbon cycle, starting with natural processes and then incorporating anthropogenic ones. Students work with a spreadsheet to see how changes in one part of the cycle affect others. They also estimate the amount of carbon sequestered in trees on their own campus and relate that to their driving habits. 


Students should be able to do the following:

  1. Describe the primary reservoirs of carbon and fluxes between them.
  2. Compare the rates of fluxes between carbon reservoirs.
  3. Describe major human impacts on the carbon cycle.
  4. Develop Excel skills, including entering equations, filling cells, and interpreting the results of computations.
  5. Compare the magnitude of carbon storage in trees to carbon dioxide produced by human activities.


Pre- and post-test using a tool similar to Carbon Sequestration Pre-Questionnaire Pilot from the Boulder Lake Environmental Learning Center (primarily just the concept-mapping exercise on the second page).

Building Blocks

Assemble the Components

The components of this lesson may be used individually, in the combination presented here, or in smaller sets, depending on the specific goals and time constraints of the instructor.

We anticipate that components 1-5 below could be performed in one or two class periods, with component 6 forming a lab and 7 being an additional part of that lab or a homework assignment. The post-test (component 8) could be given at the end of the lab or in a later class period.

Note that components 1-5 give a global picture of the carbon cycle, and components 6-7 bring the story down to a local (and even individual) level. Both perspectives are important for students.

  1. Use the concept-mapping exercise as a pre-test.
  2. Introduce the global carbon cycle using the modified Figure 7.3 from the IPCC report (2007; this figure does not include anthropogenic influences but do not allude to this yet). Emphasize the differences in timescales between the geological processes and the biologically driven processes and the balance between sources and sinks.
  3. Show IPCC Figure 7.3 for increases in atmospheric CO2 and CH4 concentrations including the human contribution. Go back to the first slide to again emphasize that we are taking carbon from the geological cycle and adding it to the biological cycle. Again emphasize the difference in rates and how long it will take for that biologically-available carbon to return to the geological reservoir.
  4. The instructor could assess student learning at this point to determine whether additional study of the carbon cycle is needed (in which case, continue here) or students are ready to move on (in which case, progress to component 5). If needed, students could use this Carbon Cycle Role-play activity in which they act out the carbon cycle with ping pong balls to further reinforce reservoirs and fluxes. *It is recommended that the instructor add reservoir cards to this activity to match the carbon cycle being used throughout the lesson.
  5. Using different scenarios, have students use the Excel spreadsheet to explore how changes in flux rates between reservoirs affect the atmospheric reservoir. The scenarios that we chose link well with our other activities that allow students to explore the role of trees on their campus and how their own use of fossil fuels influence the carbon cycle. Other scenarios can be presented. While this spreadsheet currently only addresses direct effects, indirect effects can be introduced using algorithms. The cells in yellow are currently changeable, but the instructor can alter the cells that are presently locked using the password "CLEAN". Changeable cells can be left blank so that the students can learn how to fill in cells and formulate equations (possibly through a jigsaw activity with different groups working through different changes), or they can be filled in by the instructor.
  6. Have students calculate carbon sequestration on their own campus. This activity, entitled Carbon Sequestration in Campus Trees, includes detailed directions in a PowerPoint, along with a practice data set (to be used initially or as the entire exercise if it is not possible for students to measure actual trees on campus).
  7. Students relate the amount of carbon sequestered on campus to the amount of carbon released by their own driving. See this handout sequestration v driving (Microsoft Word 35kB May16 12) for suggestions on how to calculate the latter (although the method for estimating the former is different).
  8. Use the same concept-mapping exercise again as a post-test.