Part 3: Import and Process Sea Ice Data

In any step, click the Show me link to reveal extra information. If you prefer a printout of the full set of instructions for this part, choose Print from the File menu.

Step 1-
Bring your data into a spreadsheet

At this point in the project Dr. Meier turns the instruction over to Thomas and Susan. They work with the students to bring their sea ice measurements into Excel and examine the trends in the data.

Open your NovemberResults.xls file in Excel by double-clicking it. Your worksheet will show 3 columns: Column A (unlabeled) shows the measurement number), Column B shows the area of ice (in pixels), and Column C shows the slice number from which the measurements were made.

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If you saved your measurement Results as a text file (.txt extension) you will need to import them into Excel.

In Excel, select File > Open. In the Open dialog box, select the option to Enable All Readable Documents. Browse to where you stored your file and open NovemberResults.txt. Use the Text Import Wizard to format the data, and save the reformatted file as a Microsoft Excel file with the file name NovemberResults.xls.

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  1. Open Excel, and use File > Open to open the NovemberResults.txt file. This will automatically open the Text Import Wizard, which formats the text data for use in the Excel spreadsheet. The data is separated (or delimited) by tabs, so click the Delimited option.text import wizard 1

  2. Leave the Delimiters option set to the default setting, Tab. Click Next.
    text import wizard 2

  3. Keep the default setting for Column data format and click Finish.
    text import wizard 3

  4. Save the file that opens as a Microsoft Excel Workbook file type, so that the file name changes to NovemberResults.xls.
    November results xls Screen Shot

Step 2-
Process your Data

  1. Check over the data to be sure you have all 28 rows.
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    Delete any rows that have duplicate slice numbers in column C. Select an extra row by clicking its row number and choosing Edit > Delete. Also, check that your slice number column contains all numbers from 1 to 28. If it doesn't, figure out which slice you missed and go back to ImageJ to measure it. If you're missing more than one year, it may actually be easiest to repeat all measurements and reimport the file. Finally, make sure the slice numbers are in order. If they are not, select all three columns and go to Data > Sort. Select the Slice number column and Ascending to have Excel reorder them.
  2. Add the word "Year" as a header label in the first column. You'll replace the numbers in this column from ImageJ with the year they represent: in cell A2 type 1978. In cell A3, type =A2+1 then copy the formula down through the rest of the column.
  3. Now that you have the years, you will not need the Slice column (Column C) so you can delete it. Select the entire column and choose Edit > Delete.
  4. Add a new column between Columns A and B. Enter a label in the top cell of the new column (cell B1). Type "Area (millions of square kilometers)."
    5. formula dialogue in excel
  5. Enter this formula in cell B2: =(C2*625)/1000000

    This will multiply the area in C2 (the number of pixels covered by ice) by the area of a pixel (625 km2) and divide by 1 million. The result will be the total ice extent (area) in millions of km2.

    • Copy this formula down column B.
    • Format the cells as numbers, and limit them to two decimal places.
    • Save your file.

Step 3-
Show the Trend in the Data

What do the data say? Is the sea ice extent really getting smaller in November of each year? Is it true that polar bears are having to wait longer for the ice to return to Hudson Bay? Graph your data to document your answer to this important question.
  1. Select the Year and Area (millions of km2) columns (columns A and B) then click the chart wizard icon or choose Insert > Chart from Excel's menu bar.
  2. Make an XY (Scatter) graph with points and smooth lines. Put Time (in years) on the X axis and Sea ice extent (in millions of square kilometers) on the Y axis.
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    chart_wizard in Excel Chart wizard dialogue
    1. Highlight the cells you are going to graph, Year and Area.
    2. Click on the chart wizard button Chart Wizard Button
      Choose "XY" scatter.
    3. Choose next, next and finish.
    Your graph should look something like this.
    area of sea ice graph in excel Sea ice graph in Excel

  3. Add a linear trendline to your graph. Click your graph, then choose Chart >Add trendline and click the Linear option.
    What does the general slope of your trendline say about sea ice in Hudson Bay since 1979? Describe the relationship shown by your trendline. At the rate of decline shown by your chart, how much ice would you predict will be in Hudson Bay in November, 50 years from now?
  4. With your chart active, click the Options tab to project your trendline into the future. Set the Forecast field to go Forward by 50 units (years).
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    trendline_options_forecast in Excel Trendline options dialogue
  5. Experiment with the trendline options. Predict the year that there will be no sea ice at all (0 square kilometers) in November.
sleds parked on shore for the summer In another village, sleds are waiting on shore for the sea ice to return.
The trend that the students find is astonishing. They decide that they will meet with the elders and discuss their findings. They prepare presentations and call a meeting for the next afternoon.

Step 4-
Save your Excel Spreadsheet and Graph.

  1. Select and copy your graph. Create a new word processing document and paste the graph into it so you can compare it with the graph you make in the next section.
  2. Save your worksheet and graph in the Excel file by choosing File > Save As... and giving it an appropriate name. Save your file in the folder with the other work for this project.

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