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Carbon Sinks and Sources


Through questioning and partnering, students gain an understanding of the complex system of carbon cycling that works to balance the levels of carbon in our atmosphere. It is important for students to understand that simple choices made every day can have profound impact in the mitigation of the effects of climate change.

Time Required: 30 minutes




Learning Objectives

Students will:
-Gain an understanding of how carbon cycling occurs
-Use questioning techniques to determine the differences between a carbon sink and a
carbon source
-Discuss how humans can influence the amount of carbon in our atmosphere

Teaching Process

Warm Up

Light the candle and ask students what they observe – candle, wick, flame. What is burning here – the wick or the wax or both? Where do they go when they are burned?
Do they just disappear forever? Blow out the candle.

Demo Activity

This experiment shows the acidifying effect of CO2 . Make an organic, non-toxic pH indicator by boiling red cabbage.
1)Boil cabbage in a covered pan for 30 minutes or microwave for 10 minutes. (Do not let the water boil away.)
2)Let cool before removing the cabbage.
3)Pour about 1/4 cup of cabbage juice into 2 see through containers. (Avoid buying plastic for this experiment. Plastic is a petroleum product. Its production process is a source of carbon emission and it doesn’t decompose.)
4)Slowly pour white vinegar in one of the containers. Observe the change in colour.
5)Then, ask a student to blow through a straw in the other container. Eventually the cabbage juice will turn colour.
Ask the students, what is the student blowing through the straw breathing out into the cabbage juice? What is the meaning of the juice changing colour? Debrief.
When dissolved in water, CO2 combines with water to form carbonic acid H2CO3. This is a weak unstable acid. However, if concentrated enough, this acid will, over time dissolve the calcium shell of marine organisms. CO2 emissions from vehicles could literally kill the Great Barrier Reef.

The Activity

Part I

1. Draw a quick illustration of the carbon cycle on the board. Give a brief definition of sinks and sources (see example in attached lesson plan). Processes that release CO2 to the atmosphere are called carbon sources. Processes that absorb CO2 are called carbon sinks.

2. Ask students for examples of processes that release CO2 to the atmosphere - carbon sources. List the sources on the board

-Point to the candle
-Us - we breathe out CO2 – we are carbon sources along with all air-breathing organisms
-Oceans and fresh water bodies (CO2 dissolves easily in water)
-Agriculture - grazing animals (cows, sheep, pigs) produce methane
-Burning fossil fuels – gas energy plants, coal, oil, gas, tar sands
-Fossil fuel production: coals, oil gas, tar sands – including the burning of natural gas during oil extraction (water, oil and gas mix) and the escape of methane (CH4) during extraction and processing of oil, gas and coal.
-Decomposing garbage in landfills/ dumps (methane)
-Rice farms (produce methane)
-Degrading farm soils: release of carbon from soils when ploughed causes it to oxidize creating CO2
-Wetland destruction
-Urban sprawl
-Decomposition of dead animal and plants with oxygen (aerobic) produces CO2
-Decomposition of dead animal or plants without oxygen (anaerobic) produces methane (CH4)

3. Ask students for examples of processes that absorb carbon dioxide from the atmosphere - carbon sinks. List the sinks on the board

-Point to a green plant – photosynthesis in plants. All green plants, peat bogs (these are
green plants in storage), growing forests: photosynthesis equation 6 H2O (water) + 6 CO2 + sunlight energy = C6H12 O6 (glucose) + 6 O2 (oxygen) glucose = carbon storage.
-Diatoms, algae
-Fossilized organic remains become fossil fuels like coal, oil and gas stored safely underground
-Oceans can absorb CO2 directly from the atmosphere.
-CO2 will stay in storage for a long time provided oceans stay cool and undisturbed. The carbon hydrate is in the slurry at the bottom in the form of sediments
-Shells, coral
-Carbonate rocks
-Wetlands – organic matter builds up at bottom of ponds providing long-term storage of carbon
-Limestone / dolomite sedimentary rocks: shale, mudstone, and coal. The Rocky Mountains are a good example of this.

4. Reiterate that this system of sinks and sources operates all over the globe and is known as the Carbon Cycle.

5. Explain to students that they are about to become either a carbon sink or a carbon source. They will not know which they are but will have to figure it out by asking questions that can be answered only by yes or no. Note: it may be necessary to demonstrate what yes/no questions sound like.

6. Hang a card on each student’s back so the wearer cannot see it.
Participants must circulate and ask others just one Yes or No question to determine what they are. They then must move onto another person, show the card and ask a question. Students should repeat until they have determined what they are.

7. Have sinks and sources group themselves into 2 groups in the room and describe who they are and how they work as carbon sinks or carbon sources.

Part II

1. Explain to students that the climate change problem lies with sinks that become sources.
Oceans: Warming oceans leading to a number of events that result in the release of carbon.
Coral die-offs, extermination of algae that take up carbon, dissolved CO2 releasing from warmer water
Limestone mining
Forests: Deforestation and forest fires
Burning of fossil fuels

2. It is the transformation from sink to source that is leading to increased global temperatures and global climate change.
As more carbon is released than can be absorbed by the naturally occurring carbon cycle, this causes changes in the amount of carbon in the atmosphere and affects how solar energy is absorbed and reflected on earth.

3. Discuss with students how the transformation of a carbon sink to a carbon source occurs. This does happen naturally, as in the case of forest fires or volcanic eruptions, but it is the increase in human activity that is upsetting the balance of carbon. Why is this happening? Is it necessary for us to undertake the activities that are releasing carbon? Point out that the amount of carbon in the atmosphere has increased 30% since the Industrial Revolution.

4. Explain that there are many small things we do every day that can either enhance or combat climate change.
Invite each student to take a Climate Change Partner card. When everyone has a card, inform students that their task is to find their partner who is, in fact, their opposite. Read out a few matching examples before playing the game, so that the students understand their task. The person with the Climate Change Combater card must find the person with the Climate Change Enhancer card, and vice versa. Once pairs have found one another, they can discuss the topic depicted on their card.

5. Once everyone has found their partners, have each pair review their cards with the rest of the class. Make note of how simple it is to make choices that combat climate change. Invite students to give other examples of simple ways to combat climate change.


Have students:

-Illustrate the carbon cycle

-Give three examples each of carbon sinks and carbon sources

-Explain the process by which a carbon sink becomes a carbon source

-Create posters depicting two or three simple ways to combat climate change.


Other Tools

-Class set of carbon sink and source “Who Am I?” and Partner cards (see attached)
-Candle and matches
-Green potted plant

For Demo:
-red cabbage to be boiled
-2 small glass containers
-white vinegar
-1 straw