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Human Energy Systems | Activity 4.4

Activity 4.4: The Seasonal Cycle (45 min)

Students watch a short video and animation about seasonal plant growth to help interpret the seasonal cycle on the Keeling Curve, and make predictions about how carbon atoms move through pools in different seasons.

Materials You Provide

  • Large pieces of poster paper (8 per class)
  • Permanent markers (4 per class)

Resources Provided


Prepare one copy of 4.4 Seasonal Cycle Worksheet for each student. You may choose to laminate the cards to keep them for future use. Follow the link for the short film to download it to your computer. Prepare a computer and projector for the film and 4.4 The Seasonal Cycle PPT. You may want to prepare the poster papers around the room as described in step 4 of the directions.


1. Introduce the Activity.

Project slide 2 of the 4.4 The Seasonal Cycle PPT and say “In this activity, we want to understand the seasonal cycle of the Keeling Curve.”

  • Using slide 2, identify the seasonal cycle in the Keeling Curve: the gray line that fluctuates up and down each year.
  • Point to the box labeled “Annual Cycle” for a close-up of the rise and fall of carbon dioxide levels in one year (the annual cycle and the seasonal cycle refer to the same cycle).
  • Tell students the purpose of this activity is to explain why this happens.


Be sure to revisit the students’ predictions on the poster paper after the animations. Discuss with them which predictions turned out to be accurate. Use 4.4 Grading the Seasonal Cycle Worksheet to check for student understanding after the activity is over. 


  • 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!
  • During the animations, use markers to circle the correct ideas that students recorded on their poster paper.


  • Have students stay at one station only and brainstorm about possible places atoms could move. Then, during the animation, have the same group edit the predictions on their poster papers to reflect the information in the animation.
  • In the 4.4 Seasonal Cycle Worksheet, have the students label the arrows with the carbon-transforming processes that cause the flux from one pool to another (cellular respiration and biosynthesis).