Wagner's and Weitzman's Bathtub Analogy
In a comment by Daniel Reeves on a recent post by my co-blogger Bryan Caplan, Reeves claims that I ignored the bathtub analogy in Gernot Wagner’s and Martin L. Wietzman’s Climate Shock in my review of the book.
I didn’t mention it but I didn’t ignore it. It just struck me when reading the book that the bathtub analogy was obviously correct and, indeed, so obvious that it wasn’t worth mentioning. Maybe that’s because I’ve read a lot about global warming, but it’s more likely due to the fact that I understand and, maybe unjustifiably, expected everyone in the debate to understand, the difference between stocks and flows.
Here’s the analogy, from page 15 of the book:
Think of the atmosphere as a giant bathtub. There’s a faucet–emissions from human activity–and a drain–the planet’s ability to absorb that pollution. [DRH note: notice how the authors jump from “emissions” to “pollution.”] For most of human civilization and hundreds of thousands of years before, the inflow and outflow were in relative balance. Then humans started burning coal and turned on the faucet far beyond what the drain could handle. The levels of carbon in the atmosphere in the atmosphere began to rise to levels last seen in the Pliocene, over three million years ago.
The authors then go on to point out that simply stabilizing the flow of carbon into the atmosphere won’t do the trick: the bathtub will fill further.
Nothing in my review contradicted this or demonstrated my ignorance of this. My review focused on other things that were problematic, like the authors’ weak criticism of geo-engineering.