Carbon Cycle

Students will learn how carbon cycles between the Earth's spheres. They will understand that there are both natural and anthropogenic (man-made) sources of carbon that are emitted into the atmosphere. They will examine the Keeling Curve data to visualize how much carbon has been emitted into Earth's atmosphere during its recent past.


1. Inform students that they will learn about the carbon cycle and the sources of greenhouse gases in the atmosphere.

2. Distribute the Carbon Cycle Exploration Sheet to each of the students.

3. Ask students to go to the Student Resources Web page and click the Carbon Cycle link.

4. Instruct students to read the content pages about the carbon cycle and answer the questions on their exploration sheets. Explain and clarify terminology and concepts as needed.

Implementation Suggestion:
- Some students may have difficulty understanding that the oscillating pattern in the Keeling curve reflects the seasonal growth of trees and plants in the northern hemisphere. During the spring and summer, trees and plants absorb carbon when they undergo photosynthesis, reducing the amount of carbon in the atmosphere. During the fall and winter, they decay, releasing carbon back into the atmosphere. You may wish to show the NASA video and animation that explains this relationship.

5. Review content and discuss aloud student responses to key questions on their exploration sheets. Ask students if they have any questions about concepts covered in the lesson and respond to their questions. Have students close their Web browser when they finish.

6. To conclude the class session, show the video clip: What does carbon dioxide have to do with global warming?

Note: The video clip is a large file. You may wish to download the video clip to your computer prior to using it in your classroom.

Materials Needed:

Video and Animation

Keeling Curve explained (Quicktime movie)

Keeling Curve animation (Quicktime movie

What does carbon dioxide have to do with global warming? (Quicktime Movie) (29 MB) Duration 1:20


Carbon Cycle Exploration Sheet (PDF / MS Word)

Assessment Information 

Carbon Cycle Assessment (PDF / MS Word)

Teacher Resources/Content Support 

Carbon in the Atmosphere

Carbon in the Atmosphere - Print Version (PDF)

Planetary Energy Balance

Planetary Energy Balance - Print Version (PDF)


Ozone - Print Version (PDF)

Greenhouse Effect

Greenhouse Effect - Print Version (PDF)