Human Energy Systems | Activity 4.4

Target Student Performance

Students use an online computer model to make quantitative predictions of how changes in photosynthesis, cellular respiration, and combustion fluxes will affect the long-term trend in the atmospheric CO2 pool.

Resources Provided

Recurring Resources


Prepare one copy of 4.4 Global Computer Model Reading and one copy of 4.4 Global Computer Model Worksheet for each student. Follow the link for the Global Computer Model short film to download it to your computer. Prepare a computer and projector for the film and 4.4 Global Computer Model PPT. You may want to prepare the poster papers around the room as described in step 4 of the directions.


1. Introduce the Activity.

Display Slide 2 of the 4.4 Global Computer Model PPT to show student where they are in the instructional sequence.


This activity includes opportunities for both formative and summative assessment.


  • You might want to point in step 5 out that although the seasonal cycle is a naturally occurring phenomenon, the current overall trend in increases in CO2 and temperature cannot be explained using evidence of natural cycles. Students may point to specific natural cycles as evidence that climate change is not caused by humans, which might include sunspots, volcanic activity, El Niño, or changes in the Earth’s rotation around the Sun. While it is true that these natural phenomena do cause variations in shorter time periods (1-15 years or so), these variations do not contradict the evidence for the recent increase in CO2 levels and temperature, especially in the last 60 years. These increases have persisted over a longer time period than natural causes like sunspots and volcanoes can explain.
  • It won’t hurt to mention a few times that the fossil fuel pool has nothing to do with the seasonal flux!

  • Have students work in pairs, with each pair using one computer and one worksheet.
  • Identify locations in the room as the three carbon pools, then have students play the role of carbon atoms moving between the three pools.
  • Project the graphs onto a white board and demonstrate how to fill them in after each move.
Extending the Learning