Just how do ‘they’ calculate the amount of carbon dioxide in the atmosphere?

The mind boggles at all the contributing factors multiplied by the margin for human error. Although “How Bad are Bananas?” takes a stab at some well-informed answers, the author admits that his conclusions are barely more than rational guesses.

For the final two days of the Sustainable Enterprise Certificate’s first session, we received a quick tour of one process with great potential for defining answers. Systems Dynamics focuses on the underlying patterns and structures that informs everything from our bank accounts to the concentration of CO2 in the atmosphere. For now, I’ll just introduce SD with a brief example.

A simple analogy: you’re drawing a bath. You stop the drain so the water doesn’t flow out again, and you open the faucet to fill the tub. In SD lingo, the tub is known as a ‘stock’, and the water is called a ‘flow.’ The water influences the contents of the bathtub; the flow affects the volume of the stock.

Now, an absurdly simple question: When the water reaches the level you desire, do you close the faucet completely, or just reduce the water’s flow? You close the faucet, of course. Simply reducing the flow won’t prevent the stock from continuing to rise. Eventually, the water will overflow.

## Seems abundantly obvious? Then let the real fun begin.

The graph below shows the number of people entering and leaving a department store over a 30-minute period.

(If you don’t think the question can be determined from the information provided, mark that as your answer.)

- During which minute did the most people enter the store?
- During which minute did the most people leave the store?
- During which minute were the most people in the store?
- During which minute were the fewest people in the store?

You’ll find the correct answers at the bottom of the post. Go take a look.

## Surprised? I was.

Remember, the graph doesn’t show the number of people in the store (the stock), but the number of people ‘flowing’ in and out of the store. Until minute 14, more people are entering the store than exiting. After minute 14, that rate of flow reverses; more people are leaving than entering.

“Of course! Such a simple oversight!”

Well, not so simple after all. In his article “Risk Communication on Climate” Professor John Sterman relates how 84% of his MIT students made the same ‘simple oversight’ in a similar activity. Instead of water in a bathtub, or people in a department store, these students were given the context of greenhouse gas concentrations in our atmosphere. (You’ll find Professor Sterman’s comments on this confusion here.)

Is it any wonder that we’re having such a hard time establishing our relationship to carbon emissions, let alone curbing them? If you’re ready for a paradigm shift and want to learn more about Systems Thinking, you’ll do well to start with Donella Meadows’s “Thinking in Systems: A Primer”

My emphatic thanks to Professor Sterman for permission to reproduce the department store activity, and to Bill Harris for patiently explaining the basics of SD over two intensive days.

**Exercise Answers:**

- Approximately minute 4
- Approximately minute 21
- Approximately minute 13
- Approximately minute 30