Carbon Dioxide Exercise

This exercise enables students to:

• Estimate changes in global carbon dioxide concentrations over a 7-year span
• Learn about variation in the carbon cycle driven by photosynthesis
• Understand how important sampling interval can be when studying changes over time
• Practice basic quantitative skills

This exercise will take at least one lecture period in a unit dealing with the carbon cycle, the atmosphere, or human impact on the environment.

Divide the class into groups of about 4 students each if possible. Groups may be as large as 8.

Data Option 1: Cut the monthly CO₂ data (Microsoft Word 24kB May3 12) into strips and put them in a hat or bucket. Have each group draw 8 data values.

Data Option 2: Use the table of randomly selected data points (Microsoft Word 84kB May3 12) from the 84 monthly values. Group number can be assigned by birthday of youngest member in group or as desired.

Give each student a copy of your version of the CO₂ exercise student handout (Microsoft Word 33kB May3 12) detailing the assignment.

Tell each group to plot their data on the CO₂ graph paper, 2005-2011 (PowerPoint 118kB May3 12).

Have each group draw a line through their data and estimate the slope and how long it will take carbon dioxide to increase to 200% of its original value. You'll need to explain that a best-fit line does not simply connect the first and last point. Have each group write their estimates on the board. There will be considerable variation. Use the CO₂ graphs, 2005-2011 (Excel 250kB May3 12) to show what the plots would like with progressively more of the 84 points included.

Now ask them why the estimates varied so much. The following lecture should deal with the interannual and intrannual variation in carbon dioxide levels. You may wish to assign homework on this topic (some is provided on the handout).

For the benefit of the instructor, here is a spreadsheet with two graphs, Keeling's data in its original format and formatted for graphing (Excel 260kB May3 12).

You may want to use current data to run this activity. The Trends in Atmospheric Carbon Dioxide website by NOAA contains continuously updated data for atmospheric CO₂ concentrations at Mauna Loa. This site is recommended for obtaining up-to-date data to use in class. The original data are stored as text file at Mauna Loa Monthly CO₂ Concentrations.

Some groups may need a little help with the quantitative elements of this exercise, so it's nice to be able to do initial plots in class, then to reinforce those skills with homework. Misplotted points will be hard to see on the individual overheads, but will stand out sharply when eight of them are stacked together. You may wish to discuss outliers with the class.

You will be able to do informal assessment of the student's understanding in class. The homework (part II of the exercise) provides an opportunity to reinforce skills and to formally assess the students' learning.

For more carbon dioxide data:

• The Trends in Atmospheric Carbon Dioxide website by NOAA contains continuously updated data for atmospheric CO₂concentrations at Mona Loa. This site is recommended for obtaining up-to-date data to use in class.
• The Ice Core Gateway: Vostok Ice Core CO2 Data (more info) has an even longer record of global carbon dioxide concentrations, with variations caused by factors other than photosynthesis and human activity.
• Atmospheric carbon dioxide record from Mauna Loa: "Atmospheric CO2 records from sites in the SIO air sampling network" (more info) has data, a bibliography, and a short description of the project.