John Sterman: Almost nothing is exogenous

“Almost nothing is exogenous,” said MIT System Dynamics Group director John Sterman in his 2002 Forrester Prize Lecture, “All models are wrong: reflections on becoming a systems scientist” (pdf).

It’s a perspective I’ve often voiced.

Here’s the key piece from Sterman’s talk:

If you ask people to name processes that strongly affect human welfare but over which we have no control, many people name the weather, echoing Mark Twain’s famous quip that ‘‘Everybody talks about the weather, but nobody does anything about it.’’

But today even the weather is endogenous. We shape the weather around the globe, from global warming to urban heat islands, the Antarctic ozone hole to the ‘‘Asian brown cloud.’’ For those who feel that global warming, ozone holes, and the brown cloud are too distant to worry about, consider this: Human influence over the weather is now so great that it extends even to the chance of rain on the weekend.

Cerveny and Balling (1998) showed that there is a seven-day cycle in the concentration of aerosol pollutants around the eastern seaboard of the United States. Pollution from autos and industry builds up throughout the workweek, and dissipates over the weekend. They further show that the probability of tropical cyclones around the eastern seaboard also varies with a seven-day cycle. Since there are no natural seven-day cycles, they suggest that the weekly forcing by pollutant aerosols affects cloud formation and hence the probability of rain. Their data show that the chance of rain is highest on the weekend, while on average the nicest day is Monday, when few are free to enjoy the out of doors. Few people understand that driving that SUV to work helps spoil their weekend plans.

In similar fashion, we are unaware of the majority of the feedback effects of our actions. Instead, we see most of our experience as a kind of weather: something that happens to us but over which we have no control. Failure to recognize the feedbacks in which we are embedded, the way in which we shape the situation in which we find ourselves, leads to policy resistance as we persistently react to the symptoms of difficulty, intervening at low leverage points and triggering delayed and distant, but powerful feedbacks.

If almost nothing is exogenous, does that affect how one might think about assumptions of objectivity and subjectivity in scenario planning?

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