What is the fate of CO2 produced by fossil fuel combustion?

Paul Quay, University of Washington
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The carbon dioxide concentration in the atmosphere is increasing as a result of combustion of fossil fuels. However, the observed atmospheric CO2 increase rate is only ~60% of the CO2 loading rate due to fossil fuel combustion. Why? We will answer this question using a box-model to simulate the earth's carbon cycle. The model will hindcast the atmospheric CO2 increase during the industrial era and compare it to the historic observations of atmospheric CO2 concentrations. The model will then be used to forecast future concentrations of atmospheric CO2 during the next century.

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Learning Goals

  • To demonstrate, using a climate-change relevant issue, the utility of simple box models to quantitatively address problems in earth sciences.
  • To demonstrate the use of a spreadsheet to construct box models.
  • To use models to demonstrate the concept of steady-state and time rate of change.
  • To examine the sensitivity of model predictions to model input.
  • To provide an opportunity for model versus data comparison.
  • To give students an estimate of the changes in atmospheric CO2 concentrations that occurred over the last century and might occur over the next century.

Context for Use

This model-based problem was used in an upper division class "Climatic Extremes" for science majors. This specific problem was given mid-way through the semester after the students had brief experience formulating 1 or 2 box models using Excel (or Matlab). Time given for solution was 1-2 weeks, depending on other class responsibilities.

Description and Teaching Materials

Activity Background (Microsoft Word PRIVATE FILE 392kB Jul29 04)
Activity Exercise (Microsoft Word PRIVATE FILE 123kB Jul29 04)

Teaching Notes and Tips

Teaching Tips-
  • Typical modeling problems
  • Possible follow up exercise
  • Assign this exercise at your own risk and, preferably, if tenured.


The students turn in an Excel spreadsheet that has the tabular data and charts of the plotted atmospheric CO2 concentrations versus time for each scenario.

References and Resources

Sarmiento, J. and N. Gruber (2002) . Sinks for Anthropogenic Carbon. Physics Today, 55(8), p.30. - This article provides excellent background for this modeling activity. The figures that appear in this activity are taken from this paper.