Proxy Variables

In addition to measuring current data points using the most advanced equipment available, it is also possible to measure some historical data points. By digging deep into ice cores in permafrost areas, as well as ocean sediment, it is possible to determine certain conditions from the distant past. Variations in the rate of formation of ice or sediment (the same is true of the rings of some trees) indicate the favorability of conditions for formation, while the presence of trace elements can also indicate various atmospheric or climatic conditions. Ice cores are of such an age that they can be used to under stand climatic conditions from half a million years in the past.

Unfortunately, of course, data observations are not always available. Only partial coverage may be possible for practical reasons, and it may not be possible to observe the desired data directly. In these cases, it is possible, with some precautions, to use proxy data. Proxy data act as substitutes for the desired data, but may differ in the time or place observed. An alternative method is to obtain data points on a proxy variable which acts in some way as an approximation of the desired data. An example of this would be the measurement of a single element or substance in the atmosphere may act as a proxy for contamination of the atmosphere as a whole, or for human impact on climate change.

There are many methodological problems with using proxies and the degree of confidence in results must generally be adjusted, accordingly. However, these are not insuperable and, when audiences are educated concerning the methods employed, their use should not lead to misunderstanding. Unfortunately, the quality of science teaching in many societies is not sufficient to enable large numbers of people to appreciate the issues concerned.

SEE ALSO: Climatic Data, Atmospheric Observations; Climatic Data, Cave Records; Climatic Data, Ice Observations; Climatic Data, Instrumental Records; Climatic Data, Oceanic Observations; Climatic Data, Proxy Records; Climatic Data, Tree Ring Records.

BIBLIOGRApHY. Richard B. Alley, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future (Princeton University Press, 2002); O. Boucher and M. Pham, "History of Sulfate Aerosol Radiative Forcings," Geophysical Research Letters (v.29/9, 2002); Barbara Goss Levi, "Warming Oceans Appear Linked to Increasing Atmospheric Greenhouse Gases," Physics Today (v.54/6, 2001); André Paul and Christian Schafer-Neth, "How to Combine Sparse Proxy Data and Coupled Climate Models," Quaternary Science Reviews (v.24/7-9, 2005); Warren M. Washington and Claire L. Parkinson, Introduction to Three-Dimensional Climate Modeling, 2nd ed. (University Science Books, 2005).

John Walsh Shinawatra University

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