February 21, 2007
Nature is too complex and depends on too many processes that are poorly understood or little monitored to be accurately depicted by models, say geologists Orrin H. Pilkey and Linda Pilkey-Jarvis.
Their book, "Useless Arithmetic: Why Environmental Scientists Can't Predict the Future," originated in a seminar to look into the performance of mathematical models used in coastal geology:
- Among other things, participants concluded that beach modelers applied too many fixed values to phenomena that actually change quite a lot.
- For example, "assumed average wave height," a variable crucial for many models, assumes that all waves hit the beach in the same way, that they are all the same height and that their patterns will not change over time; but, the authors say, that's not the way things work.
- Also, modelers' formulas may include coefficients (the authors call them "fudge factors") to ensure that they come out right.
- And the modelers may not check to see whether projects performed as predicted.
Two different issues, the authors say, illustrate other problems with modeling:
- One is climate change, in which, they say, experts' justifiable caution about model uncertainties can encourage them to ignore accumulating evidence from the real world.
- The other is the movement of nuclear waste through an underground storage site at Yucca Mountain in Nevada, not because it has failed -- it has yet to be built -- but because they say it is unreasonable to expect accurate predictions of what will happen far into the future -- in this extreme case, tens or even hundreds of thousands of years from now.
Given the problems with models, should we abandon them altogether? Perhaps, the authors say. Their favored alternative seems to be adaptive management, in which policymakers may start with a model of how a given ecosystem works, but make constant observations in the field, altering their policies as conditions change. But that approach has drawbacks, among them requirements for assiduous monitoring, flexible planning and a willingness to change courses in midstream. For practical and political reasons, all are hard to achieve.
Source: Cornelia Dean, "The Problems in Modeling Nature, With Its Unruly Natural Tendencies," New York Times, February 20, 2007.
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