# Exploration 3B

## Calculating the Rate of Change (Slope) of Temperature

The interactive time-series graphing tool just showed trend lines and slopes using a calculation in the program. However, it is possible to calculate the slope of a line if you know two points on the line. To do this, you calculate the change in the y value or the temperature anomaly over the change in the x value or time in years. Follow the directions below to calculate the approximate slope of each trend line for the 100-, 75-, 50- and 25-year time intervals. Remember that the slope is the rate of change.

**Trend Lines For the past 125 Years**

- Click on the trend line for 100 years. Choose a data point near the beginning (left side of graph) that is on the line or as close to the line as possible. Enter the beginning year and the beginning temperature anomaly in the table.
- Choose an ending year that is on the line or as close to the line as possible. Enter the ending year and the ending temperature anomaly in the table.
- Calculate the change between beginning and ending years AND the change between beginning and ending temperature anomalies. Enter these values in the table.
- Use the equation above to calculate the slope of the line between the two points you chose.

- Repeat steps 1-4 to complete the table.
- How similar is this slope using two points on the line to the one calculated under the graph on the website? If there is a difference, why do you think that is?