Prerequisite Knowledge and Objectives
Before beginning this lesson, students should already know how to plot a point and create a scatter plot. Students will demonstrate their understanding by completing the warm-up.
By the end of this lesson, students should be able to determine the type of correlation that exists between two variables and the significance of that correlation. Students will demonstrate a basic understanding by completing the exit ticket, homework, and ultimately their capstone project.
Deforestation Video
Download and play the video A Convenient Truth from the FAO*. The amount of video shown should depend on the students' familiarity with the carbon cycle. If students have a limited understanding, you may choose to show more of the video. Whereas, if students have already studied the carbon cycle in science or gleaned enough information from the activity in lesson one, then you may only need to play the beginning segment on how trees absorb carbon from the atmosphere. This segment will serve as an introduction to the next activity.
∗Created and posted by the Food and Agricultural Organization (FAO) of the United Nations (to download, go to the web address http://www.fao.org/forestry/52980/en/)
Deforestation Activity
As you heard and saw in the video, the greenhouse gas carbon dioxide is absorbed by trees. One of the increasingly problematic issues is that deforestation reduces the number of trees. Logically, it stands to reason that with fewer trees, we'll absorb fewer greenhouse gases and the temperature of the atmosphere will rise. However, how can we show this relationship? Through experimentation, of course. In the next activity, we'll run a simple experiment, collect and graph the data, and look for patterns.
Students will divide into four teams. Each team should be comprised of a different number of students; e.g. 2, 4, 6, 8. Each team will start on one end of the room and must run to the opposite end to collect as many balloons as they can in one minute. When students return to the original side of the room, they must drop their balloons in their team's basket. At the end of the minute, have a student record the number of balloons each team collected on the board. Students will organize the data into a table and then create a scatter plot. For even better results, repeat the experiment to increase the number of data points you have to plot. Use this activity as a lead-in for a discussion on correlation.
The game can be modified so that larger groups can play. Instead of having everyone play at once, students can play multiple rounds and record the data after each round. This could allow for data collection with up to 20-25 students all at once. Also, if technology is available and students are already proficient with graphing by hand, a student could enter the data directly into a graphing calculator and then create a scatter plot in that manner. This could serve as the perfect opportunity to teach technology and to discuss window settings. While using technology prevents students from practicing plotting points, it could save time, especially if the students don't need to practice plotting points. Students should still practice labeling the scatter plot appropriately and defining the variables.
Discussion on Correlation and the Relationship Between Deforestation and Global Warming
Point out that experimental/survey data are rarely (if not ever) perfect and that differences in skill or behavior can impact results. This idea can also be seen when plants of the same species undergo photosynthesis at different rates. This could be a result of the soil in which the plants live or the amount of exposure the plant has to light each day. This may also explain why the data are scattered and not lined up perfectly as we saw in our previous lesson (Lesson 1 Activity 1) when we were given a specific pattern to follow. Scatter plots do not provide a definitive relationship between two variables, but allow us to analyze patterns that emerge.
Turn to the student-produced scatter plot on the board. Ask the students to describe the data. What's going on in the graph? Are there any patterns? What happens to the number of balloons collected as the group size gets larger? This should be an example of a positive correlation. As the independent variable increases, so does the dependent variable. Refer to Figure 1 for an example of a positive correlation.
Significance of the game: each player represents a tree and the balloons the players collect symbolize greenhouse gases absorbed from the atmosphere. Regardless of athleticism, teams with more players should be able to collect more balloons. As the number of trees decreases, what happens to the amount of greenhouse gases that are absorbed? Correlation allows us to name patterns that exist in data, which helps us identify the type of relationship that exists.
Lastly, discuss the other types of correlation that exist: positive, negative, strong, weak, or none. Of course, we want to be as specific as possible when discussing correlation, so we can have strong or weak positive correlations or strong or weak negative correlations.
Figure 1
Practice Identifying Types of Correlation
Have the students practice identifying the type of correlation that exists by providing the students with a number of scenarios. For example, what kind of relationship do students think exists between the number of greenhouse gases in the atmosphere and the number of people diagnosed with asthma each year? Diagnosed with malaria? How about the number of cars purchased around the world each year and the amount of oil reserves remaining? Ask the students to create a hypothesis and then explain their reasoning.
After the discussion, distribute the following short articles for the students to read:
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"Climate Change Linked to Rise in Malaria, Asthma": http://www.usatoday.com/weather/climate/2005-11-02-climatechange-disease_x.htm (June 3, 2010) discusses the effects of greenhouse gases and climate change on the spread of diseases like malaria and asthma.
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"Falling Oil Reserves Put World at Risk": http://energy-conservation.suite101.com/article.cfm/society-set-to-run-on-empty-as-oil-runs-out (June 15, 2010) discusses the possibility of running out of oil and briefly mentions how car productions impact oil reserves.
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Closing: Boobquake (Audio Clip: Wait, Wait, Don't Tell Me; show date 5/1/10; clip time within show 8:15-11:15; can be downloaded free of charge from iTunes)
Overview of Audio Clip:
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Iranian cleric claimed that earthquakes were God's punishment for scantily clad women.
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Indiana woman refutes claim of the existence of boobquakes. Organizes a day of nakedness, which was followed by a 6.9 earthquake on the Richter scale.
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Background Information
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About 500,000 earthquakes occur each year, 100,000 of which can actually be felt. The majority of large earthquakes take place in the Pacific Ring of Fire, a horseshoe shaped zone that follows the Pacific coasts of the Americas, Asia, and Australia.
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Natural earthquakes are caused when tectonic plates slide against or on top of one another. The intensity of an earthquake is measured on the Richter magnitude scale. Any earthquake measured above a 6.0 is considered strong, as clear vibrations can be felt above ground. Approximately 120 6.0-6.9 level earthquakes occur each year.
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Information was taken from Wikipedia.org (http://en.wikipedia.org/wiki/Earthquakes)
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Discussion/Cliff Hanger
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We know that earthquakes occur all the time at a variety of magnitudes, and that natural earthquakes result from shifts in tectonic plates. Yet here was an experiment that attempted to disprove a correlation, but really gave further evidence of the cleric's hypothesis.
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If correlation does not indicate causation, why do we care about it? What does correlation tell us?
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Homework
Add the eleven definitions (listed earlier in the unit under "Vocabulary") I provided to your vocabulary flashcards. Remember to define the words using your own version of the definition.
