Activity:

HOW WHEN AFFECTS WHAT

Part 2: Is It Getting Hot or Not?

* From Aspen Global Change Institute 1992 - Ground Truth Studies

Objective

Students will critically interpret graphical data, and evaluate the difficulties inherent in interpreting and forecasting long and short term trends.

Background

During the past 20 years, much attention has been given to the potential climatic effects of increasing concentrations of atmospheric greenhouse gases. The graphs of ground-based temperature measure-ments on the following pages show that there was little trend toward increasing or decreasing tempera-ture during the 19th century, a marked increase of about 0.5° from 1910 to 1940, followed by a period of erratic and dramatic temperature fluctuations from 1940 to 1970, and then followed by a sharp increase in temperature to the present. All six of the warmest years in the global record have occurred since 1980. Some scientists see a trend of increasing global temperature in this data. Others emphasize the large amount of variability in the global temperature record, arguing that Earth has not warmed as much as predicted by climate modelers, thereby implying no evidence of global warming. Against this backdrop of controversial trends, government policy makers must consider whether they need to take action to reduce greenhouse gas emissions or not. Some policy makers oppose any specific timetables for combating global "warming," citing lack of agreement among scientists on the problem. Others wish to establish specific targets of cutting the pollution that causes greenhouse gases (i.e. carbon dioxide, etc.). This exercise encourages students to examine the process and draw their own conclusions by analyzing the actual data which is the basis of the controversy. They will extend the under-standing gained in Part 1 of this activity to global mean temperature change, observing how the sample or window they choose effects the outcome of their study. The data presented here was compiled by P.D. Jones, T.M.L. Wigley and P.B. Wright from the Climatic Research Unit of the University of East Anglica in England.

Materials

Four graphs of global mean temperature, each representing the difference between the actual measure-ments for the years indicated and the average for 1951-80; the first from 1882 to 1894; the second from 1944 to 1956; the third from 1978 to 1990; and the fourth from 1854 to 1990.

Procedure

  1. Divide the class into four groups and give each group one of the four global mean temperature graphs. The groups cannot share data. Students will study their sample of temperatures and ob-serve how readings fluctuate from year to year. From their samples, they should theorize and sup-port whether there is evidence that global temperature was rising, falling, or remaining constant.
  2. After the students have spent some time studying their graphs, ask them to project what global surface temperature will be 10, 20, and 50 years into the future.
  3. Have each group present their predictions for 10, 20, and 50 years in the future.
  4. Let the students from the first three groups compare their estimates with the longest term graph.

Discussion

  1. Compare the four sets of predictions and consider the reliability of each. Discuss the implications of basing conclusions on limited data and the patterns that could be inferred from considering each of these subsets. The pitfalls of basing conclusions on limited data sets should become obvious.
  2. How much data is needed to make reliable predictions? Have students develop a list of things they would need to find out in order to prove that their projections were valid.
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Last modified prior to September, 2000 by the Windows Team

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