Human Energy Systems Unit Activity 1.4: Drawing a Trend Line Carbon: Transformations in Matter and Energy Environmental Literacy Project Michigan State University

Finding overall trends Look at this graph. This shows places where the temperatures were hotter or colder than average in the winter of Look at the Great Lakes region in North America. Then, look at the entire globe.

Finding overall trends If we relied only on the data about temperature in the great lakes region of North America, we might think that the entire planet was having a very cold winter. However, when we look across the globe, we see a different trend.

What is the global trend? Turn and Talk: find a partner and describe the overall trend you see in the global temperatures in the winter of Be prepared to share your description with the class.

Describing the global trend Below, combine answers from the class to construct an overall description of the global trend from the winter of Classroom description: (write class ideas here)

Positive and Negative Trends This graph has a negative trend because the trend line goes down from left to right. This graph has a positive trend because the trend line goes up from left to right. Just like in the global temperature graph, trends are difficult to see when the data are “messy” or “noisy.” When you have a scatter plot graph, sometimes it helps to draw a trend line. That makes it easier to see which direction the data are moving. In this activity, we are going to practice drawing trend lines.

Different kinds of trend lines This trend line (the blue line) is straight because it was calculated using a mathematical formula that considers every data point in the graph. There are lots of ways to draw trend lines. Sometimes we use a mathematical formula to calculate a straight line that shows us the general trend. Other times we calculate averages over time. This trend line (the red line) is curvy because it was calculated using a 5 year running average, which only considers data points in five year periods.

Practice Making Trend Lines On your worksheet, practice making trend lines for two graphs. One graph is new: this shows ice cover on lake Superior. The other graph is familiar: this is the arctic ice graph that you created in the previous activity.