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NOVA scienceNOW: Capturing Carbon

Viewing Ideas

Before Watching

  1. Examine the structure of a leaf. Pair students and have them inspect leaves from different plants and trees. Have them make drawings or rubbings, and describe the shape and size of each leaf. Then ask them to research the parts of the leaf and label their drawings. Discuss the advantages and disadvantages of various shapes and sizes. (e.g. leaves have pointed tips to shed water, pine needles are very narrow leaves which shed snow easily) Leaves are adapted to their function and their environment, allowing optimum access to sunlight, air, and water.

    Discuss the role of a leaf in photosynthesis, the process by which a plant turns light energy (sunlight) into chemical energy (glucose or sugar). Below is a simplified version of the photosynthesis equation:

    carbon dioxide + water + light energy → carbohydrates (chemical energy) + oxygen + water

    Focus on the role of carbon dioxide. Air (which contains .05% carbon dioxide) enters the leaf through stomata on the underside of its leaves. The location of the leaves on a plant, and their shape, effects the amount of sunlight they absorb and how air flows around the plant.

    Extension 1: Germinate beans and allow them to grow to the two- or four-leaf stage. Snip off the terminal bud which is actively growing. This will limit the photosynthesis to the existing leaves. Using petroleum jelly, coat the tops of all the leaves on one plant, and coat the undersides of all the leaves on a second plant. Leave the third plant as is; it will serve as the control. Place all three in a place where they receive sunlight, and water them as you would normally, treating each plant the same. Observe the plants each day for a week or more, noting their health and growth. (The control should do well; the plant with the tops of the leaves coated should do nearly as well as the control, and the plant with the underside of the leaves coated will wilt and begin to die. Plants take in air, and thereby carbon dioxide, through stomata on the undersides of their leaves; when the stomata are blocked by the petroleum jelly, the plant does not get the CO2 it needs for photosynthesis and will eventually die.)

    Extension 2: Submerge a fresh-cut leaf (e.g., aquatic plant leaf or geranium) in a container of water and place the container in bright sunlight. After about one hour, have students examine what is happening on the leaf's surface; a magnifying glass may help. Students should see tiny bubbles on the leaf. The oxygen bubbles are a result of photosynthesis.

  2. Explore carbon dioxide. Discuss with students that carbon dioxide (CO2) is a vital, though relatively small, part of Earth's atmosphere, with concentrations of about 385 parts per million (.038%). It is a greenhouse gas, contributing significantly to the heat-retaining capabilities of our atmosphere. Carbon dioxide is also found in Earth's oceans, (dissolved in seawater), at concentrations much higher than in the atmosphere. It is used by plants as part of photosynthesis and produced by plants and animals during respiration. It is also produced as a byproduct of burning fossil fuels and during the decomposition of organic matter. It is used by human beings for everything from carbonating soda to making plastics to putting out fires. Carbon dioxide exists as a gas at normal room temperatures and pressures, turns directly from a solid (dry ice) to a gas at very cold temperatures (below -78°C ), dissolves in water and other liquids. Carbon dioxide can exist in all three states and can be dissolved. This adaptability opens many avenues to sequestering it. (The only way to mitigate the effects of carbon dioxide in the atmosphere is to sequester it. Sequestration is a process that traps atmospheric carbon dioxide.)

    Perform the demonstrations below and ask students questions to encourage them to think about the properties of carbon dioxide.

    Safety Warning: Wear goggles when handling the materials below and during each demonstration.

    • Carbon dioxide in seltzer: Demonstrate that water can contain carbon dioxide by simply opening a fresh bottle of seltzer or sparkling water. Gas bubbles will form in the water the instant you release the pressure, because the high pressure inside the sealed bottle allows more carbon dioxide to dissolve in the water than would dissolve at typical atmospheric pressures. (Carbon dioxide can be stored in water under pressure.)

      Extension: Calculate the amount of carbon dioxide in seltzer. Place a bottle of seltzer water or soda on a scale and record its weight. Shake the bottle, wait until the foam settles a bit, and then very slowly and carefully open the cap, releasing the carbon dioxide while not spilling any of the liquid. Repeat this until the bottle stops (or mostly stops) changing in weight. (In general, there is about 2 grams of CO2 per 454 milliliters, or 16 ounces, of seltzer.)

    • Carbon dioxide from vinegar and baking soda: Carefully pour about 2 tablespoons of vinegar into a plastic bottle and spoon about 1 teaspoon of baking soda into a balloon. Stretch the mouth of the balloon over the mouth of the bottle, being careful not to spill any of the baking soda into the bottle. Lift the balloon so that the baking soda pours into the bottle, and observe what happens. (Pressure will build so you may want to keep one hand around the neck of the balloon where it is stretched over the mouth of the bottle.) When the baking soda and vinegar come in contact with each other, a chemical reaction occurs, and carbon dioxide is produced, and the balloon inflates.

    • Carbon turns neutral water into acidic water: Before class, prepare a solution of bromothymol blue (an acid-base indicator) by adding several drops of bromothymol blue (available from pet stores) to a small bottle of distilled water. In class, pour small amounts of this solution into four or more separate glasses.

      • Glass 1: Add a known base, such as baking soda or ammonia. (Bromothymol blue is blue in basic solutions.)

      • Glass 2: Add water. (Bromothymol blue is also blue in neutral solutions.)

      • Glass 3: Add a known acid, such as vinegar or lemon juice. (Bromothymol blue is green and yellow in acidic solutions, with the color becoming more and more yellow as the acidity increases.) Consider using more than one acid to demonstrate this variability in color.

      • Glass 4: Have a student blow GENTLY through a straw into the bromothymol blue, slowly bubbling the solution, being very careful not to drink any of the solution. (Dissolved CO2 forms carbonic acid, so the solution gradually turns to a yellowish-green.)

  3. Model the greenhouse effect: The greenhouse effect is a natural, vital part of how Earth maintains its temperature range. The greenhouse gases in the atmosphere trap heat, forming a blanket around the Earth. Since the mid-1850s, humans have continually added carbon dioxide, which is a greenhouse gas, to the atmosphere. This extra carbon dioxide increases the heat-holding capacity of the atmosphere, disrupting Earth's temperature-management system. This disruption is often called global warming. Scientists are trying to remove carbon dioxide from the atmosphere. To examine carbon dioxide's ability to absorb heat, have the class do the experiment below. Test this experiment before having students perform it.

    Safety Warning: Wear goggles, and have students wear goggles, when performing the activities and handling the materials below.


    • three thermometers
    • three clear, sealable plastic bags
    • 2 teaspoons baking soda
    • 2 tablespoons vinegar
    • one beaker
    • black paper


    1. Place a thermometer in each plastic bag.

    2. Seal one of the bags with as little air inside as possible.

    3. Seal a second bag with as much air inside as possible.

    4. Hold the third bag wide open so that it has as much air inside as possible and then carefully pour extra CO2 into this bag from a beaker of baking soda and vinegar;

    5. Seal the third plastic bag, containing as much CO2-rich air as possible.

    6. Record the temperature measured by each of the thermometers.

    7. Place all three bags on the black paper. Expose them to direct sunlight for 10 to 30 minutes. (Consider watching the while the bags are being exposed to the sun. On a very sunny day, the changes may be fast and some thermometers may reach their peak temperature.)

    8. Check the thermometers regularly, observing the changes in temperature.

    9. Discuss why each one is different.

    [When sunlight enters Earth's atmosphere, some of that energy is absorbed (by the atmosphere and by Earth's surface) and reradiated as heat. Some of this heat energy escapes into space, but the greenhouse gases in Earth's atmosphere trap much of it. Similarly, the gas in the bags traps heat energy, causing the temperature to increase. Since CO2 is an important greenhouse gas, the bag with additional CO2 usually traps more heat. (NOTE: As with any demonstration, the results should, but do not necessarily, match those expected. If the temperatures in the bags do not support the role of greenhouse gases in heat capture, discuss the nature of scientific experimentation, including the importance of multiple trials, control of conditions, and measurement challenges.]

    Extension: Observe the temperatures in the three plastic bags after they have been removed from the sunlight. The same differences in temperature that occur during heating can sometimes be observed while the bags are cooling. The thermometer in the bag with little air will cool most rapidly, without its "blanket" of trapped warm air, and the thermometer in the bag with CO2-rich air will cool most slowly, with the extra greenhouse gas helping to trap the heat inside the bag.

After Watching

  1. Discuss global warming. There is strong scientific agreement that global climate change is real and is largely due to human activities. For example, in 2004, the Washington Post printed an article titled, Undeniable Global Warming, which reported that of 928 "global climate change" abstracts published in scientific journals between 1993 and 2003, 75 percent accepted that are planet's climate is changing and humans are partly responsible. The other 25 percent of the articles didn't disagree; they simply dealt with specific aspects of global climate change and didn't address whether or not humans play a role. Given this consensus, why is there controversy?

    Discuss the topic of why global climate change and why the roles humans play in it are so controversial. Discussion questions might include: What kinds of attitudes and behaviors serve to keep things as they are? Why might business and industry interests resist stricter rules, regulation, taxation, or public education campaigns? Why might people resist changes that could reduce their own carbon footprints? As appropriate, prompt them to discuss the following:

    • the importance of fossil fuels in our daily lives, and the effects on our lives if we made significant changes

    • the economics of gasoline, factories, cars, etc.

    • the economics of changing industries and infrastructure over to a new model

    • the nature of scientific knowledge and the difference between "global warming is an absolute fact" and "based on the available evidence, Earth's climate seems to be changing"

  2. Calculate your carbon footprint. In recent years, people concerned about global climate change and their role in that change have adopted the idea of a carbon footprint, a measure of how much carbon dioxide a person is responsible for putting into the environment. Some sources of carbon dioxide considered in a carbon footprint are relatively direct, such as driving a car to school or turning on the; even breathing! Other sources sometimes considered are a bit farther removed, such as those that went into the manufacture and shipping of products bought at the store, or even the bags used to carry those items home. Once one understands his or her carbon footprint and the factors that contribute to it, he or she may begin to make changes to reduce it.

    A number of carbon footprint calculators are available on the Web, including one developed by the U.S. Environmental Protection Agency. Have your students use this carbon calculator to calculate their own carbon footprints, and have them discuss the many sources of carbon dioxide in their lives, as well as ways that they can (realistically) make changes.

  3. Perform experiments using limewater to learn about carbon sequestration: In the segment, Professor Klaus Lackner introduces the concept of carbon sequestration, the storage of carbon in the ocean, underground, and biosphere repositories. He then extends the idea to another process, called mineral sequestration, which is the storage of carbon in serpentine rock and similar mineral structures. According to Klaus, this process takes Mother Nature hundreds of years. He and his graduate student Sam Krevor are working on a way to shorten the time. However, you and your students can easily experiment with binding carbon and forming rock. Specifically, you can demonstrate the formation of limestone, or calcium carbonate, from the combination of carbon dioxide and lime.

    Safety Warning: Wear goggles, and have students wear goggles, when performing the activities and handling the materials below.

    At least one day before class, gather and prepare the necessary supplies:

    • lime (also called pickling lime or the chemical, calcium hydroxide)
    • hot water (distilled water works best)
    • a spoon
    • filter paper
    • glass quart-sized jars with lids
    • glasses
    • straws

    Prepare the limewater:

    1. Fill half of the jars with hot water.

    2. Add about 1 tablespoon of lime to each jar (or 1 tablespoon per liter of water).

    3. Stir thoroughly.

    4. Secure the lids.

    5. Let the solution sit overnight. (The solution will start milky white; after sitting, it should appear clear, with precipitate at the bottom. Precipitate is a solid formed in a solution during a chemical reaction.)

    6. Pour the clear liquid through filter paper into the clean jars, (If you don't use filter paper, avoid transferring any of the precipitate.)

    7. Secure the lids on the new jars, which now contain saturated solutions of limewater.

    Have students demonstrate that their breath includes carbon dioxide. Pour a small amount of limewater into glasses, and have students blow GENTLY through straws into the limewater (being very careful not drink any of the liquid). As students blow into the limewater, it will gradually change from clear to milky white. Below is a simplified version of the reaction equation:

    limewater + carbon dioxide → limestone + water

    The way to express this chemically is:

    calcium hydroxide + carbon dioxide → calcium carbonate + water

    The way to express this using chemical symbols is:

    Ca(OH)2 + CO2 → CaCO3 + H20

    The lime in the water combines with the CO2 in the students' breath to form limestone (i.e. calcium carbonate) a white powder (precipitate) suspended in the liquid. (As when you prepared the limewater, if these glasses of milky solution are left to sit, the limestone will settle to the bottom.) To show that it is the carbon dioxide in their breath and not some other gas that's reacting to the limewater, consider repeating the experiment using another source of carbon dioxide, such as dry ice, seltzer, or baking powder and vinegar.

    Extension 1: Use your limewater to take carbon dioxide out of the air. Fill a glass with limewater, let it sit somewhere safe and exposed to the air for about a week, and pour off the remaining liquid., The white material remaining in the glass is limestone.

    Extension 2: Use vinegar to separate the lime and carbon dioxide again. Add vinegar to a glass containing limestone and observe what happens. Bubbles of carbon dioxide form, and gradually, the limestone exposed to the vinegar disappears. Any limestone not in contact with the vinegar, such as high up on the glass's sides, will remain.

    Extension 3: Test rocks for the presence of limestone. Gather a collection of rocks, including sedimentary rocks, marble (if possible), and chalk. Pour vinegar on them and observe what happens. Rocks that contain limestone will bubble, as carbon dioxide is released.

Links and Books

Web Sites

NOVA scienceNOW
Offers resources and information related to capturing carbon.

U.S. Department of Energy: Carbon Sequestration
Provides information and news on various carbon sequestration research, projects, and plans.

EPA: Climate Change
Offers links to information on the science, effects, policies, and economics of global climate change, as well as recommendations on what people can do.

NASA Earth Observatory: Carbon Cycle
Offers a sequence of information on the carbon cycle.

NOVA: Warnings from the Ice
Companion to another NOVA program, which addresses the changes taking place in the coastal ice on the Antarctic Peninsula.


The Change in the Weather: People, Weather, and the Science of Climate
by William K. Stevens.
Delta, 1999.
Discusses the science of climatic change.

New Approaches on Energy and the Environment: Policy Advice for the President
by Richard D. Morgenstern and Paul Portney, Editors.
RFF Press, 2004.
Contains "memos" to the United States President (written before the 2004 election) on a variety of important policy-related topics, including energy and climate.

They All Laughed... From Light Bulbs to Lasers: The Fascinating Stories Behind the Great Inventions That Have Changed Our Lives
by Ira Flatow. New York:
HarperCollins, 1992.
Provides an entertaining look at various scientific discoveries and inventions.

The Weather Makers: How Man Is Changing the Climate and What It Means for Life on Earth
by Tim Flannery.
Atlantic Monthly Press, 2006.
Describes global warming and its implications.

Activity Author

Teon Edwards is a curriculum developer with a background in astrophysics, mathematics, and the use of technology and multimedia in teaching and learning. Since 1996, she has developed numerous science and mathematics education materials for school, home, and informal learning environments.

"Undeniable Global Warming" by Naomi Oreskes. Washington Post: Sunday, December 26, 2004; Page B07.

Teacher's Guide
NOVA scienceNOW: Capturing Carbon