This post is by Phil, not Andrew.

Over the couple of months I have seen quite a few people celebrating the long-awaited launch of a big device that will remove plastic garbage from the Pacific ocean. I find this frustrating because this project makes no sense even if the device works as intended: at best it will turn out to be a good piece of technology that is deployed in a stupid location where it will cost a lot of money to maintain while removing much less plastic than it could otherwise.

Every now and then I hear similar enthusiasm being expressed for devices that will remove carbon dioxide from the atmosphere…just build these things all over the place and you can solve or at least reduce the problem of excessive atmospheric carbon dioxide. As with the ocean cleanup, if you have such a technology you’d be a fool to deploy it this way.

As many readers of this blog will have already recognized, if you are trying to remove plastic from the ocean, or to remove carbon dioxide from the atmosphere, the place to do it is where the concentration is highest. If you have a device that can separate plastic from water, put it in or near the outflow of a river that is bringing the plastic into the ocean; don’t wait until the garbage-filled water has been diluted by a factor of many thousand. The device can only remove plastic from the water that it interacts with, so it can only process a certain volume of water per day; much better if that water has a high concentration of the plastic you are trying to remove. Similarly, if you have a technology that can separate carbon dioxide from other gases, you should put it in or near smokestacks from power plants and cement plants…that is, places where the concentration is much higher than you find if you wait for the gases to be fully mixed into the rest of the atmosphere.

The situation with the Pacific Garbage Patch cleanup is especially bad because, in addition to the (very large) inefficiency that is due to putting the devices in places with unnecessarily low concentrations of floating plastic, there are farther inefficiences associated with putting the devices far, far out at sea, where they are more costly to maintain than if they were closer to land.

All of the above seems pretty obvious, and I daresay it is pretty obvious to most readers of this blog. Why, then, are so many people excited about the idea of putting a bunch of devices way out in the Pacific, or sprinkling carbon dioxide removal devices all around the globe? I don’t know but I have a theory: I think people make a cognitive error, or perhaps experience a cognitive illusion, in which they don’t count the input stream as part of the system in a logical way. I had some interesting and somewhat perplexing conversations with friends who are enthusiastic about the carbon dioxide removal idea, and I think that’s a nice clean example of the cognitive error that I’m talking about so I’ll focus on that one.

I’ve discussed the carbon dioxide removal approach with several friends at various times, and said that if there is a good technology for separating carbon dioxide from other gases it should be used at major carbon dioxide sources, not in the general atmosphere. All of them express some variation of this sentiment: We need to stop emitting carbon dioxide, but we also need to remove carbon dioxide from the atmosphere because carbon dioxide concentrations are already too high. Putting the devices in places where they remove carbon dioxide from ‘the atmosphere’ seems like it is actually solving the problem, whereas decreasing the amount of carbon dioxide that is emitted is merely a way of stopping things from getting worse.

But of course, taking N tons of carbon dioxide out of the atmosphere and taking N tons of carbon dioxide out of a stream of combustion gases that is entering the atmosphere have the same effect on atmospheric carbon dioxide concentrations. And if, by putting your device at the smokestack, you can remove 3N tons in the same time and for the same cost, you are much better off putting the device in the smokestack. But somehow this doesn’t appeal to people because it doesn’t “reduce the carbon dioxide concentration in the atmosphere.” It’s almost like they would prefer to add 3N tons to the atmosphere and then remove N tons, than to add zero tons in the first place; after all, in the former case you are removing N tons of carbon dioxide from the atmosphere, and in the latter you aren’t removing anything! They love the idea of removing the pollutant; decreasing the rate at which it is added just doesn’t seem the same somehow, even though it is.

I think this error, or something close to it, clouds people’s thinking about ocean plastics too.

The situation is more complicated with ocean plastics: 97% of plastic that enters the ocean does not end up in the “Great Pacific Garbage Patch” so if you want to remove plastic specifically from the ‘patch’ then maybe you do want to put your device there. But I’ve talked to people about this and they seem to agree that they do want to decrease the amount of plastics in the oceans in general, not just in the middle of the Pacific Ocean. But still, they seem to think that a device that removes plastic from the Pacific Ocean is needed, and they’re much more excited about that than about preventing plastic from entering the Pacific Ocean. One of my friends said “we need to do both.” Well, no: if it’s more effective to just do one of them, then that’s what we should do.

The Ocean Cleanup project is probably going to collect many tons of garbage from the Pacific Ocean (at great expense) and I’m sure some people will declare it a success…and that’s a crying shame because they could do much, much better for a lot less money.

This post is by Phil, not Andrew.