Bathtubs, waistlines, and credit cards

A challenge: to come up with a metaphor for the problem of cumulative emissions of greenhouse gases that is appropriate, compelling, and accessible.

Here’s a bit of context to explain why I think such a metaphor is necessary. Yesterday, Val, Jon, and I facilitated a workshop on climate change for High School students. It was a short workshop (75 minutes), and we set some ambitious goals for ourselves: first, to have our participants realize that individual sacrifices (turning off the lights, taking public transit, going vegetarian, etc.), while certainly beneficial, would not be enough to stop climate change even if they somehow, improbably, convinced the rest of the world to follow suit. Then, we wanted to help them understand the problem systemically —for instance, to identify the actors that are blocking the introduction of climate policies and to explore their motivations and worries. Finally, based on the previous points, we wanted our participants to think again about what they could to to fight the problem, not (just) from the point of view of individual sacrifice, but of social change: to organize, to lend support to groups that share their goals, and to push policymakers to do the right thing.

I think we managed to reach our goals for some of our participants, but not for all. Partly this was due to our time constraints and the experimentation and rough edges in our workshop’s design, but also, partly, because of the lack of intuitiveness of the problem of climate change. For instance, to understand that personal choices won’t be enough we need to realize the urgency and the permanence of the issue. Let me explain:

If we’re camping out and light a bonfire, we can clearly see the smoke coming out of the fire. We can trace some of that smoke in the sky, but it dissipates quite quickly, and it’s gone in seconds; if we put out the fire it seems to leave no trace in the sky. When Beijing hosted the Olympics its government prepared by doing the equivalent of putting out the fire: close down some factories, restrict the use of cars, etc. Air quality wasn’t great, but it was acceptable. Intuitively, then, we think that eventually we can get our act together and, through some breakthrough technology or some strict policy measures, we can bring carbon emissions down as much as we need to and avoid catastrophic climate change: the smoke will dissipate.

The problem of course is that the “smoke” cannot dissipate any further, it already has and there’s already too much of it. There’s nowhere else to dissipate. The oceans and the forests absorb only a fraction of the carbon dioxide we emit; most of it stays up there for decades. The pollution we are generating today, those same molecules, will still be around warming the atmosphere of our grandchildren.

For the mathematically inclined, this is easy to visualize as a calculus problem: what matters is not the end point of our greenhouse gas emissions curve at some particular year, but the area under that curve. In other words, it’s not our emissions any given year that matter, but our cumulative emissions over history. This is what is unintuitive about the problem; even Bill Gates doesn’t seem to get it.

But we can’t just walk to a group of High School students and say that they should focus on decreasing the area under the curve of greenhouse gas emissions. We need a better way to explain the concept. So far I know of three metaphors to explain it; generally they seem unsatisfactory to me:

The first is the Bathtub metaphor. The National Geographic explains it well: “As long as we pour CO2; into the atmosphere faster than nature drains it out, the planet warms. And that extra carbon takes a long time to drain out of the tub.”

Carbon Bathtub, from the National Geographic

The Bathtub metaphor uses a commonplace artifact to explain the problem, which is great. But it doesn’t seem intuitive: unclogged bathtubs usually don’t overflow (unless your faucet has a really high pressure). Water, at least bath water, is clean and good —and why should we want an empty tub anyway, if what we want is to take a bath? Furthermore, there’s an essential asymmetry here: greenhouse gases go up; water pours down into the tub. I’ve found this metaphor many times, so I’m used to it, but I can tell when I try it with other people that something isn’t quite working with it.

The second is the Waistline metaphor: if we eat more calories than we burn, our waistline grows. This metaphor neatly uses our common knowledge (being overweight is unhealthy and dangerous), so in some ways it’s better than the Bathtub metaphor, but it also has some undesirable implications. First, we can lose weight by eating less or by burning more calories. But environmentally speaking, the equivalent of burning more calories (afforestation) is not nearly enough –the metaphor offers two potential and, to an extent, alternative solutions, but we need to crank up on both. Second, there’s that nagging association with personal choice: if I decide to lose weight, I can do it, on my own. And third, perhaps most importantly, the metaphor does a bad job at conveying the idea that the area under the curve is what matters. If I lose weight this year it doesn’t really matter that much that last year I was overweight –I’ve solved my problem.

Finally, the third is the Credit card debt metaphor. If I pay some of my old charges but incur in greater charges every month, I’ll never pay off my debt. I think I like this one the best because it has the nice feature of incorporating feedback loops into the problem: my old charges generate interests, so the more I get in debt the harder it is to get out of it —drawing a parallel with climatic feedback loops, such as the albedo effect and the acidification of the oceans. There’s also a morality tale going on: I probably got in debt because of my reckless spending. But again, the metaphor is problematic because it emphasizes individual choice and sacrifice. It also cannot really be used with students effectively, since I doubt many of them (or Bill Gates) have had credit problems.

So. Do you have an accessible and compelling metaphor to explain this problem? I, and many others, would love to hear it.


About Jorge Aranda

I'm currently a Postdoctoral Fellow at the SEGAL and CHISEL labs in the Department of Computer Science of the University of Victoria.
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4 Responses to Bathtubs, waistlines, and credit cards

  1. yonoleo says:

    How about a methapor that illustrates the point by using speed and momentum? Just brainstorming, you could have an object moving towards another very hot object. The closer it gets, the hotter it gets. Pollution can increase the size of the object as well as the speed (maybe it is a train that gets more cars attached to it when pollution grows). Then, by reducing your pollution you can see that the train you need to stop as well as the energy you need to stop it is still massive.
    Maybe pullotion only affects the mass of the object while the capacity of the earth to get rid of the pollution affects the speed of the train. My physics are rusty, but these capacity could be shown as the incline on the train tracks. At this point, even if the earth could get rid of more pollution than we are creating (making the train go uphill), we would still get warmer because all of the pollution that’s accumulated already (the train would still move forward because of its momentum).
    I’ll think more about it.

  2. Valeria says:

    Jorge, the workshop was such a learning experience. I really admired your commitment to explaining the science. Sometimes I think that the work I do when teaching how to effect change is very abstract but you pushed for the understanding of the problem, which I think was very needed. I’m glad you’re writing about it. You rock!

  3. Pingback: Do try this at home | Serendipity

  4. Peter says:

    Great use of analogy!
    Recently I started posting interestnig analogies I found on the web on I thought it could be a good idea to create a place where people can share useful analogies. Check it out!

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