Inflows and Outflows

One basic – but still often misunderstood – point about climate change is that the human species is adding CO2 to the atmosphere at roughly twice the rate of net removal. In other words, every year more than half of the CO2 we add to the atmosphere accumulates there, creating a heat-trapping blanket. Every citizen should know this fact and understand its implications:

1. Freezing emissions at current rates would lead to constantly increasing LEVELS of CO2 in the atmosphere, because every year we'd be adding more CO2 than the Earth could remove.

2. Stabilizing CO2 levels would require cuts in emissions of 60-80%.

3. Lowering CO2 levels would require even deeper cuts than this.

It is more challenging than you might expect to convey this set of ideas.

Systems thinkers often use the metaphor of a bathtub and describe our current situation as one in which the tub is filling twice as fast as it is draining. A wonderful short paper by John Sterman and Linda Booth-Sweeney, Why We Can't Wait, uses this metaphor very effectively.



One thing that has always troubled me, though, is that the metaphor of bathtub, while instantly helpful for understanding why emissions cuts of more than half are needed, breaks down in trying to help people understand how heat is trapped by rising levels of CO2. To help with this, in my presentations I represent the level of CO2 in the atmosphere as a thickening ring (or blanket) around the Earth.




This provides a simple, visual way to picture what happens if emissions exceed the rate of removal.



The real communications prize would go, I think, to the metaphor that combines both bathtub and blanket. In my presentations I stretch accuracy a bit and ask people to picture a blanket made of many layers. I ask them to picture the layers constantly being added (emissions) and removed (net removals). As long as emissions are larger than removals the blanket will grow thicker, trapping more heat. It's not elegant, but it works, providing an image people seem able to hold in their minds.

Still, I'd love it if some creative thinker came up with a better bathtub-blanket than that.

Anybody?