Atmospheric Carbon: Can We Offset the Increase?

Joceline Boucher, Corning School of Ocean Studies, Maine Maritime Academy

This activity is part of the On the Cutting Edge Exemplary Teaching Activities collection and has been reviewed by 1 other review process

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This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

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This page first made public: May 22, 2013

Summary

This activity lets students discover first hand how the big issues in climate change -- here, the increase in atmospheric CO₂ and the utility of carbon offsets -- can be understood through measurement, application of simple concepts, and "back of the envelope" estimates. It also provides students both personal and global context for understanding the magnitude of current greenhouse gas emissions.

Greenhouse effect, Greenhouse gas emissions, Mitigation of climate ...(more) | College Lower (13-14), College Upper (15-16) | Online Ready

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Context

Audience

I use the activity in the classroom with a non-majors, Chemistry In Context course, and for homework in an elective course, Changing Oceans, intended for marine science and marine biology majors. The activity would be ideally suited to an environmental chemistry course or a science-based course in climate change.

Skills and concepts that students must have mastered

Students need a rudimentary knowledge of chemistry (mole concept; ideal gas law) to do this activity.

How the activity is situated in the course

The activity serves as a "prequel" to a unit on ocean acidification, and could be used to introduce carbon sequestration or the concept of carbon footprints. It could also be used after a unit on greenhouse gases.

Goals

Content/concepts goals for this activity

This activity builds familiarity with climate change vocabulary and enables students to demonstrate, from simple calculations, that other sinks beside the atmosphere must exist for anthropogenic carbon emissions.

Higher order thinking skills goals for this activity

Problem solving
Analysis of graphs
Reflection on societal concerns

Other skills goals for this activity

This activity will help to build numeracy skills.

Description and Teaching Materials

The activity can be done in small, in-class groups, following a unit on greenhouse gases and the enhanced greenhouse effect. It might also be assigned for homework prior to a unit on ocean acidification.

Student Worksheet for Atmospheric Carbon Activity (Microsoft Word 130kB May18 13)
Answer Key for Atmospheric Carbon Activity -- private instructor-only file

Teaching Notes and Tips

Most students will have forgotten the formula for the volume of a sphere, but usually one or two will remember and can be encouraged to share.

Because my students are mostly from Maine, the worksheet uses this location as an example where reforestation could occur. It's not a very good example, since Maine is already about 90% forested. Instructors may wish to substitute another place in this part of the exercise. Nowak et al. (2013; see link below) provide carbon uptake estimates for urban tree planting; the IPCC report (link below) provides uptake ranges for boreal, temperate, and tropical forests.

After the activity, I like to show a website offering carbon offsets through tree planting (find these by searching for "buy carbon offset".)

Besides showing that reforestation cannot offset anthropogenic emissions of CO₂, the activity could also prompt a class discussion on the climatic feedbacks associated with tree planting and changes in land cover (see Caldeira et al. link below).

Assessment

I usually grade this activity as check/check-plus/check-minus.

References and Resources

Caldeira, K., Gibbard, S., Bala, G., Wickett, M. E., & Phillips, T. J. (2005, December). Will growing forests make the global warming problem better or worse?. In AGU Fall Meeting Abstracts (Vol. 1, p. 03). Online: http://adsabs.harvard.edu/abs/2005AGUFM.B31D..03C

Nowak, D. J., Greenfield, E. J., Hoehn, R. E., & Lapoint, E. (2013). Carbon storage and sequestration by trees in urban and community areas of the United States. Environmental Pollution, 178, 229-236. Online: http://www.ncrs.fs.fed.us/pubs/jrnl/2013/nrs_2013_nowak_001.pdf

Watson, R. T. (2000). Land use, land-use change, and forestry: a special report of the intergovernmental panel on climate change. Cambridge University Press. Online: http://www.ipcc.ch/ipccreports/sres/land_use/index.php?idp=151

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