1. Tell students that this lesson will begin with an activity that compares the variable amounts of CO₂ found in four different gases, namely, the air, our breath, car exhaust, and the product of a chemical reaction between baking soda and vinegar. Divide the class into groups of two to four, and distribute the Bringing the Greenhouse Effect Down to Earth Worksheet (Student Version) Document . Before they get started, remind students to use caution with all materials and to wear safety goggles at all times.
Note: This activity was adapted with permission from an early draft version of "Sampling Carbon Dioxide," in Chapter 5, pages 44-47, of the book Climate Change in the Global Systems Science (GSS) project series. Copyright 2004 by the Regents of the University of California. The latest version can be found at Global Systems Science . The GSS project materials are produced by the Lawrence Hall of Science, University of California, Berkeley.

2. Now that students have explored CO₂ levels found in different gases, they can begin to examine CO₂ levels on a more global scale. Show students the graph in the CO2 Concentrations at Mauna Loa Observatory, Hawaiʻi Document , also known as the Keeling Curve. Discuss the following questions as a class. The discussion should lead students to the idea that the increase in CO₂ as seen in this data may indicate that increasing human dependence on burning fossil fuel for energy is affecting the atmosphere on a global scale. This will tie in to the next resource.

1. Describe the trend in the levels of CO₂ in the atmosphere over the past 50 years.
2. By what percentage has the concentration of CO₂ in the atmosphere increased since 1958?
3. Note the periodic oscillation (zigzag pattern) in the concentration of CO₂. How do scientists distinguish between "normal" oscillations and a departure? What is the time period of each oscillation? What could cause these oscillations? (Note: The answer is the loss of foliage in the Northern Hemisphere during the winter months. However, this may not be obvious to students because they know it is summer in the Southern Hemisphere at this time. They may need help understanding that, because there is so much more foliage in the Northern Hemisphere than in the Southern Hemisphere, the loss of that foliage is significant enough to cause the drop in CO₂ from its level during the summer months.)
4. Why is this periodicity important to interpreting the data?
5. Why is Hawaii one of the more ideal locations to collect atmospheric CO2 as a model of the concentration for the world?
6. How does this data collected at Mauna Loa tie in to scientists' recent predictions about climate change and global warming?

3. Continue the discussion of the relationship between climate change and global warming by showing students the Global Warming: Graphs Tell the Story Document . Discuss the following questions:

1. Do you think that the graphs provide evidence of a correlation between human use of fossil fuels and the temperature and CO₂ levels in the atmosphere? If so, which graphs show evidence of a correlation?
2. Should we be concerned about the changes that are occurring in the environment due to technology? Why or why not?

4. The effect of global warming on our environment can be seen most dramatically by looking at glaciers and ice caps. Have students work in pairs and watch the Earth System: Ice and Global Warming Video . Ask students to answer the following questions in their journals:

1. Why are glaciers indicators of climate change?
2. Some of the factors that affect input and output of a glacier are temperature, precipitation, humidity, and reflectivity. Which appears to be the most important? Why?
3. List some reasons why a decrease in glacial ice could increase the temperature of Earth.

5. Bring the class back together and have students share some of their responses to question (c) in Step 4. Then show students the Mountain of Ice: If the Ice Melts Interactive . Discuss the following questions:

1. Why does this resource show how these areas looked 20,000 years ago? What was the climate like at that time (where was all the water)?
2. In what ways does sea ice serve as a "canary in the mine shaft"? In other words, how does it serve as a warning system?
3. What is the worst-case scenario for the world in these diagrams? How would you measure the volume of ice, and how would you calculate the rise in sea level?
4. Imagine that by 2100, the sea level has risen 2 feet. What effects would this have on humans? List and explain as many as you can think of.
5. How are the changes in sea ice a good example of a positive feedback cycle? (The cycle is as follows: The less ice there is, the greater the absorption of solar radiation, the higher the temperature, and the more ice that continues to melt — and vice versa.)

6. Tell students that they will now look closer at human contributions to global warming by examining the use of fossil fuels. Break the class into pairs or small groups and have them watch the Snapshot of U.S. Energy Use Video . (Note: This video jumps into a discussion of power plants. You may wish to tell students that the first few lines are talking about how power plants are online and operating 24 hours a day to meet the demand for electricity.) Have students discuss the following questions in their groups and record responses in their journals.

1. What are some of the energy sources used to meet humans' ever-increasing demand for power?
2. What are some ways that we release CO₂ into the atmosphere every day?
3. On the average, each person in the United States produces over 20 tons of CO2 each year; collectively, this country produces 25 percent of all CO₂ released into the atmosphere worldwide. Should the United States reduce its energy use? Why or why not? How much of the personal 20 tons per year is due to automobile usage?

7. Tell students that they will now calculate how much CO₂ their family contributes to the atmosphere each year — just from vehicle use. Divide the class into small groups and ask them to take out the Family Mileage Record Worksheet Document they used to estimate how much their family drives or rides in a typical week. Students will use this data to calculate how much CO₂ their family produces in a year. Distribute the Family CO2 Contribution Worksheet Document to students. Tell them to complete their calculations, and then have them answer the following questions:

1. How much CO₂ does your family contribute to the atmosphere in a year? How does this compare to the 20 tons produced on average by each person in the U.S.? (Keep in mind that you are comparing family usage to individual usage. You may want to first calculate how much each person in your family uses on average, then compare it to the national figure.)
2. How might you and your family reduce the amount of CO₂ that you generate? Note: Students may focus on the type of car(s) that their family owns — a factor that is often out of their control. Help them move toward other ideas, such as carpooling (dividing the family mileage by the number of people in the carpool), making fewer trips to the grocery store, walking, etc.
3. If time allows, asks students to calculate how much their ideas from (b) could reduce the amount of CO₂ their family generates.