The Butterfly Effect


The father of Chaos Theory, Dr. Edward Lorenz, died last week. Among his many contributions to science was the Butterfly Effect. He gave a talk about predictability entitled "Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?"

The correct answer is no, but that's not what a lot of people believe, even though their common sense tells them otherwise.

Lorenz discovered how weather models, computer simulations, were sensitive to initial conditions. An extremely small change in one parameter often results in a model going in a very different direction from the previous run. This is why the IPCC does not use computer models to make predictions about climate change, and offers instead scenarios that illustrate possibilities.

Some scientists believe the butterfly effect also exists in the atmosphere, although they can't prove it. Two climate blogs I follow have been debating this: Real Climate and Climate Science. The discussion goes back to 2005, when Roger Pielke Sr published the following comment on Climate Science. It's from Professor Richard Eykholt, an expert on chaos and nonlinear dynamical systems, referring to Pielke's previous post, What is the Butterfly Effect.

I think that you captured the key features and misconceptions pretty well. The butterfly effect refers to the exponential growth of any small perturbation. However, this exponential growth continues only so long as the disturbance remains very small compared to the size of the attractor. It then folds back onto the attractor. Unfortunately, most people miss this latter part and think that the small perturbation continues to grow until it is huge and has some large effect. The point of the effect is that it prevents us from making very detailed predictions at very small scales, but it does not have a significant effect at larger scales.

Posted: Wed - April 23, 2008 at 03:29 PM          

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