# Climate Change Lesson 4 : The Carbon Cycle : Sources and Sinks

Note: The Keeping Up with Carbon video (found on the Climate Change Resource DVD) reviews previous lessons and is a good introduction to this lesson. It can also be used at the end of this lesson as a review.

1. Dynamics of the carbon cycle.

Where does carbon dioxide in the atmosphere come from and where it does it go?

The general formula for photosynthesis is:

6CO2 + 6H2O + sunlight = C6H12O6 + 6O2

(photosynthesis)

C6H12O6 + 6O2 = 6CO2 + 6H2O + Heat

(respiration or burning)

Plants absorb CO2 and water, and through the process of photosynthesis produce large carbon molecules (sugar, wood, plants). Animals, including humans, eat plants and use the stored solar energy releasing heat through the process of respiration. Plant life that decays or is burned also releases carbon dioxide, water vapor and energy. This is a natural and integral part of the earth’s environmental system.

Show the NASA video Carbon Cycle on the MEECS Climate Change Resource DVD.

Discuss the main points:

• Carbon is exchanged between the oceans, solid earth, biosphere and atmosphere through various natural processes. (Slide 2)

–– What two processes between the biosphere and the atmosphere cause the largest exchanges? (photosynthesis and decomposition)

• For thousands of years, the processes that added and subtracted carbon dioxide from the atmosphere were in balance. (Slide 3)

–– Are they in balance now? (no)

–– What does the video give as the reason for the imbalance? (dependence on fossil fuels)

–– How does this cause the imbalance? (When we burn fossil fuels for heat, transportation, and electricity, large quantities of carbon that would otherwise remain stored in the solid earth are released into the atmosphere in the form of carbon dioxide)

2. Explore the carbon cycle.

The atmosphere exchanges CO2 continuously with the oceans. Regions or processes that predominately produce CO2 are called sources of atmospheric CO2, while those that absorb CO2 are called sinks. (Slide 4)

Show students the Carbon Cycle transparency master. (Slide 5) Have students point out the carbon dioxide sources (where carbon is released) and sinks (where carbon is absorbed or stored).

Use the Explore the Carbon Cycle student activity to categorize the sources and sinks for carbon dioxide. Students should be encouraged to explain their reasons for choosing source or sink.

3. The Carbon Cycle in Michigan.

Give students a laminated copy of Michigan’s Land, Air, and Water poster. (Slide 6) In small groups students circle as many land-use sources of greenhouse gases as they can find pictured on the poster. Chart these with type of greenhouse gas (carbon dioxide, methane, nitrous oxide, other), and the process that produces the gas (respiration, burning, etc.) on the Michigan’s Land, Air, and Water student activity sheet.

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