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Human Energy Systems | Activity 1.4

Activity 1.4: Drawing a Trend Line (20 min)

Students discuss various strategies for how to identify trends in two examples of data sets: global temperature anomalies and Lake Superior ice cover.

Materials You Provide

Resources Provided


Print one copy of the 1.4 Drawing a Trend Line Worksheet for each student. Prepare a computer and projector to display the presentation. Retrieve students’ completed worksheets from the previous activity with their graphs of arctic sea ice data.


1. Revisit the students’ arctic sea ice graphs from the previous activity.

Return the graphs of arctic sea ice from Activity 1.3 to each pair of students. Ask them to look at their graph for two minutes and describe what information the graph conveys in words to each other. Tell them that “overall” is the key word here: instead of looking at each individual point on the graph, they should look for the general “trend” that is emerging when all of the data points are put together.

  • Pass out one copy of 1.4 Drawing a Trend Line Worksheet to each student. Have them write a short description of the trend that they see in their arctic sea ice graph on the first part of the worksheet.
  • Ask students to share their initial descriptions of the overall trend of the arctic ice graph. At this point, listen to their ideas, but do not correct their ideas.
  • Ask questions that will help reveal how the students came to their conclusions like: Can you tell me more about how you decided that? Or Who can add to that? Or Who had a similar or different description? Or How is your description similar or different?


This activity contains numerous opportunities for formative assessment. First, see how students describe the global trend of temperature anomalies in step two. Next, see what explanations they provide when you ask them to predict how much arctic sea ice will be on Lake Superior in five years. Do they confidently make a prediction, or do they suggest that they cannot predict due to the variation in the graph? Finally, monitor how easily they are able to construct the trend line on the Lake Superior graph in step four. If they have trouble with either of these, you may want to revisit these steps before moving to the next Activity.


  • When watching the video, students may need help identifying the difference between the seasonal flux of ice between winter and summer, and the overall trend of decline.
  • If students are having trouble identifying a trend in the data, have them calculate an average of the stars on the left side of the graph and the stars on the right side, and then draw a line going through the two new averages. This should make the negative trend very clear.


For more advanced math students, consider having them constructing the trend line from the scatter plot using point-slope form. This video includes a short tutorial: and

Extending the Learning

Have students find data sets online that they can transform into scatter plots and then calculate the trend.