Useless Arithmetic: Why Environmental Scientists Can't Predict the Future

When coastal engineers decide whether to dredge sand and pump it onto an eroded beach, they use mathematical models to predict how much sand they will need, when and where they must apply it, the rate it will move and how long the project will survive in the face of coastal storms and erosion.

Orrin H. Pilkey, a coastal geologist and emeritus professor at Duke, recommends another approach: just dredge up a lot of sand and dump it on the beach willy-nilly. This “kamikaze engineering” might not last very long, he says, but projects built according to models do not usually last very long either, and at least his approach would not lull anyone into false mathematical certitude.

Now Dr. Pilkey and his daughter Linda Pilkey-Jarvis, a geologist in the Washington State Department of Geology, have expanded this view into an overall attack on the use of computer programs to model nature. Nature is too complex, they say, and depends on too many processes that are poorly understood or little monitored — whether the process is the feedback effects of cloud cover on global warming or the movement of grains of sand on a beach.

Their book, “Useless Arithmetic: Why Environmental Scientists Can’t Predict the Future,” originated in a seminar Dr. Pilkey organized at Duke 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.