1. Activate students' prior knowledge about carbon dioxide in the Earth system.

Tell students that matter cycles throughout Earth's system and that matter is not destroyed as it moves throughout the system. Ask:

• What are some sources of carbon dioxide? (Carbon dioxide is emitted when organisms respire and decay, as well as when materials are burned.) 

• Where is carbon stored when it is not carbon dioxide? (The elements in carbon dioxide came from foods and fuels.) 

• Where does carbon dioxide go after it's released into the atmosphere? (Carbon dioxide in the atmosphere can be taken up by plants during photosynthesis, or it can be absorbed by the ocean.)

2. Discuss the role of uncertainty in the scientific process.

Let students know that in this activity they will be asked questions about the certainty of their predictions. Tell them to think about what scientific data are available and the evidence they get from the model as they assess their certainty with their answers. Encourage students to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

Explain that science is a process of learning how the world works and that scientists do not know the “right” answers when they start to investigate a question. Tell students they can see examples of scientists' uncertainty in climate forecasting.

Show the Global Temperature Change Graph from the 1995 IPCC (Intergovernmental Panel on Climate Change) report. Tell students that this graph shows several different models of forecast temperature changes. Ask: Why is there more variation (a wider spread) between the models at later dates than at closer dates? (There is more variation between the models at later dates than at closer dates because there is more variability in predicting the far future than in predicting the near future.)

Tell students that the ability to better predict near-term events occurs in hurricane and tropical storm forecasting as well. Project The Definition of the National Hurricane Center Track Forecast Cone and show students the “cone of uncertainty” around the track of the storm. Tell students that the cone shows the scientists' uncertainty in the track of the storm, just as the climate models show the scientists' uncertainty in how much Earth's temperature will change in the future. Ask: When are scientists most confident in their predictions? (Scientists are most confident in their predictions when they have a lot of data. This is why the forecast for near-term events is better than forecasts of longer-term events, both in storm forecasting and in climate forecasting.)

Tell students they will be asked questions about the certainty of their predictions and that they should think about what scientific and model-based data are available as they assess their certainty with their answers. Encourage students to discuss the scientific evidence with each other to better assess their level of certainty with their predictions.

3. Discuss the role of systems in climate science.

Tell students that forecasting what will happen in Earth's climate system is a complicated process because there are many different interacting parts. Scientists think about how one part of the system can affect other parts of the system. Give students a simple example of a system, as described in the scenario below.

On an island, there is a population of foxes and a population of rabbits. The foxes prey on the rabbits. Ask: 

• When there are a lot of rabbits, what will happen to the fox population? (It will increase because there is an ample food supply.) 

• What happens to the fox population when they’ve eaten most of the rabbits? (The foxes will die of starvation as their food supply decreases.) 

• What happens to the amount of grass when the fox population is high? (The amount of grass will increase because there are fewer rabbits to eat the grass.)

• If there is a drought and the grass doesn’t grow well, what will happen to the populations of foxes and rabbits? (The rabbit population will decrease because they have a lesser food supply. The fox population should also decrease as their food supply decreases.)

Humans introduce dogs to the island. The dogs compete with the foxes over the rabbit food supply. Ask: What will happen to the populations of foxes, rabbits, and grass after the dogs are introduced? (The foxes will decrease because they are sharing their food supply, the rabbits will decrease because they have more predators, and the grass will do well because of the lowered impact of the smaller rabbit population.)

Tell students that these simple cause-effect relationships can expand into more complex system relationships. Let students know that they will be exploring cause-effect and system feedback relationships between carbon dioxide and water vapor in this activity. Ask students to think about how each piece of the system affects other pieces of the system.

4. Introduce and discuss the use of computational models.

Introduce the concept of computational models, and give students an example of a computational model they may have seen, such as forecasting the weather. Project the NOAA Weather Forecast Model, which provides a good example of a computational model. Tell students that:

• scientists use information about the past to build their climate models.
• scientists test their climate models by using them to forecast past climates.
• when scientists can accurately forecast past climates, they can be more confident about using their models to predict future climates.

5. Have students launch the Sources, Sinks, and Feedbacks interactive.

Provide students with the link to the Sources, Sinks, and Feedbacks interactive. Divide students into groups of two or three, with two being the ideal grouping to allow groups to share a computer workstation. Tell students that they will be working through a series of pages of models with questions related to the models. Ask students to work through the activity in their groups, discussing and responding to questions as they go.

NOTE: You can access the Answer Key for students' questions—and save students' data for online grading—through a free registration on the High-Adventure Science portal page.

Tell students this is Activity 4 of the What Is the Future of Earth's Climate? lesson.

6. Have students discuss what they learned in the activity.

After students have completed the activity, bring the groups back together and lead a discussion focusing on these questions:

• Show the biogeochemical cycle of carbon (file in media carousel). Ask: Is there a source that does not act as a sink? (No. All of the sources of carbon in the Earth system are also sinks for another source.)

• In the Earth system model with ocean and water vapor (Model 5), how did the level of carbon dioxide affect the amount of water vapor in the atmosphere? (When the carbon dioxide level is high, the temperature is high, because carbon dioxide is a greenhouse gas. The higher temperature causes water to evaporate from the surface, leading to more water vapor in the atmosphere.)

• What is the effect of water vapor on temperature? (Water vapor increases temperature because water vapor is also a greenhouse gas.)

• What is the feedback relationship between carbon dioxide level and water vapor level? (It is a positive feedback relationship. When carbon dioxide is high, the temperature is higher, leading to more evaporation of water and lower solubility of carbon dioxide, leading to higher temperatures, leading to more water vapor and still lower solubility of carbon dioxide, leading to higher temperatures, and so on.) 

• Is the Earth system model with ocean and water vapor (Model 5) a good model of the Earth system? (No. This model is not a good model of the Earth system. The temperature keeps going higher and higher, which is not realistic. There is something missing from this model.)