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.
READER COMMENTS
Thomas Lee Hutcheson
Sep 18 2021 at 11:14am
The difference between “emission” and “pollution” always lies in the relationship between volume emitted, the absorptive capacity of the environment, and the external harm from a given level of concentration. CO2 is no different from Mercury or particles from smokestacks, or municipal sewage.
David Henderson
Sep 18 2021 at 1:37pm
You write:
It’s actually quite different from municipal sewage. If you really believe what you’re saying, then you should be indifferent between breathing air with CO2 in it and air with sewage emissions. Are you?
AMT
Sep 18 2021 at 2:17pm
Come on, even you know from the context that’s obviously not what he’s saying. The point is that something is only pollution if it causes harm, not that CO2 and sewage are literally identical. If I play my stereo very loud in my backyard and no one is around, there is no noise pollution for anyone. If it is 3am and my neighbors are trying to sleep, then it is noise pollution. If our GHG emissions are below what can be absorbed by the planet, they cause no harm and are not pollution.
Jon Murphy
Sep 18 2021 at 2:30pm
AMT-
There’s a lot of things going on in your comment. I’m not sure I follow. For example, you write:
Except clearly there are countless cases where emissions do cause harm even if they can be absorbed by the planet. Horse emissions were causing massive harm in cities prior to the invention of the automobile (cholera outbreaks, etc), and yet those emissions could easily be absorbed by the planet.
Another thing. You write:
But note that is the opposite of what the authors say. They use “emission” and “pollution” interchangeably.
AMT
Sep 18 2021 at 4:57pm
I am clearly responding to what Hutcheson said and David’s incredibly disingenuous response. It appears the authors of this book are a bit sloppy in their usage of the word pollution, and I would guess they use the term interchangeably because, at the margin, our emissions are pollution, which is the whole point of their bathtub analogy…they could be more precise, but I think it’s quite meretricious to criticize people who clearly understand exactly what the issue is.
I said GHG emissions, because that is what the topic is, it’s not any potential harm regardless of whether the earth can absorb it or not. So when people talk about GHG emissions, they mean, obviously, emissions concerning global warming. To clarify, GHGs can obviously also cause harm completely unrelated to global warming, but that’s not what we’re talking about, and you know it. Yeah, the CO2 building up in a closed garage from a vehicle running also creates pollution to the occupant of the vehicle, even if the earth can absorb it…what a great criticism of a book about global warming?! This is incredibly disingenuous. It should also be obvious since I even gave another example completely unrelated to global warming of noise pollution, which obviously is easily absorbed by the planet…the issue is the harm caused. Your horse example does nothing to contradict that point. To reiterate the obvious point I already stated “The point is that something is only pollution if it causes harm.”
Thomas Lee Hutcheson
Sep 19 2021 at 6:50am
I mean that the local environment can absorb an emission fast enough to keep the concentration below a harm-causing concentration. I hike on a trail with evident horse emissions, but the amount is too low to cause any annoyance.
Jon Murphy
Sep 19 2021 at 10:07am
Yes, that was one of the points you made. But you also made a contradictory point:
That’s where the confusion about what it is you are actually saying comes in.
Matthias
Sep 19 2021 at 2:15am
Yes, there are doses at which I don’t care.
Too much CO2 in the atmosphere is toxic for humans. (Though that’s far above ‘climate change’ levels.) And very small amounts of sewage aerosols or so are totally fine.
David S
Sep 19 2021 at 4:39pm
I think even this bathtub analogy is extremely misleading. For a real analogy, try this:
Think of a bathtub (that is the atmosphere, about 5.5 x10^15 tons), with an eyedropper dripping CO2 into it at 3 drops per year (that is natural sources, 750 x10^9/year). To this, we add another 1.5 drops every 10 years (all human emissions, 32.5 x10^9/year).
The bathtub drain, as I understand it, is so sensitive/responsive that it drains all of the natural sources, and half of the human emissions. This is way more sensitive than a bathtub drain, which would essentially drain the same amount no matter how many drops of water were dripped in.
For a slightly better analogy, make the 1.5 drips every tens years be dyed. And then have the dye slightly float, because for some reason only half of human emissions are re-absorbed. (But that could just be time-lag, as I understand it – I haven’t followed this too closely.)
Calling it a bathtub and a faucet is incredibly misleading, more than 7 orders of magnitude off.
(a standard bathtub hold 42 gallons)
(scaled to a 42 gallon atmosphere, the flow due to natural causes is 0.16 mL, a drop of water is 0.05 mL)
(bathtub faucet flow rate is approximately 4 to 7 gallons per minute – way too large unless a minute is several million years, and obviously humans should not try to predict our technology a million years out)
Knut P. Heen
Sep 20 2021 at 12:13pm
The bathtub is not an elastic equilibrium system. If you put enough potatoes in the bathtub, it will fill up and overflow. If you put a lot of potatoes on the market, the price will fall and the potatoes will be absorbed by the increase in demand. If you put even more potatoes on the market, the price will fall even more until the price is zero. The market is an elastic equilibrium system until the price is zero.
The carbon cycle is an elastic equilibrium system. Dead plants and organisms are buried to eventually form coal and oil. Digging up these and burning them will send carbon back to the atmosphere. Plants grow by absorbing CO2. Animals eat the plants. More carbon in the atmosphere will create a new equilibrium with more life on earth. The planet has become significantly greener since the 1970s according to NASA (https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth).
By the way, 3 million years is nothing in geological time. The Earth is 4.6 billion years. The Pliocene was the last period before the one we are living in. The CO2-concentration in the atmosphere has been exceptionally low the last period. Levels above 1000 ppm have been common during the last 500 million years.
I am currently more concerned about the excessive plant growth in my garden due to CO2-emissions than global warming.
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