One of the bankrupt ideas of Robert Moses, as told in The Power Broker by Robert Caro, was that building more roads would fix the traffic problem. “Some city planners noticed that the traffic pattern on Long Island had fallen into a set pattern: every time a new parkway was built, it quickly became jammed with traffic, but the load on the old parkways was not significantly relieved” (p. 515).
Caro argues that new road supply induced a near-offsetting increase in demand, as people drove more and bought more cars in response to Moses’ bridges and highways. The futility Caro evokes—new supply failing to solve the problem it was built to solve—reminds me of a common argument over the metals and minerals needed for clean energy products.
Right now, the copper, nickel, and cobalt needed for transmission wires and batteries comes from terrestrial mining (mining on land). There are also large deposits of these metals lying deep on the ocean floor, 4000 to 6000 meters below the surface. They take the form of “nodules”, soft golf-ball sized lumps, and they sit on top of the broad, flat abyssal plain. It is technologically possible to send a collector vehicle, like a Mars rover, to the ocean floor, suck up the nodules like a vacuum cleaner, and send them up in a tube to a vessel waiting above on the ocean surface.
The regulator, the International Seabed Authority, has not yet allowed commercial collection of deep seabed nodules. In the meantime, the argument I keep having with scientist and lawyer friends is whether such seabed mining would be good. Mining hydrothermal vents or seamounts seems more damaging; in this post I am writing exclusively about nodule collection.
I think it would be good because my guess is that terrestrial mining is more ecologically harmful than nodule collection would be. Intuitively, land is more hospitable to life than the deep seabed, so if there could be less terrestrial mining in exchange for nodule collection, then I think this would benefit wildlife. My conversation partners dispute this, but more fundamentally some of them dispute the preceding necessary condition that nodule collection would substitute for terrestrial mining at all.
Would nodule collection reduce terrestrial mining?
To assess this, we need to know the supply elasticity of terrestrial mining. If nodule collection increases the supply of refined copper, nickel, and cobalt, reducing the prices of these metals, would the quantity of terrestrial mining change? If the supply elasticity is zero, then nodule collection would be an ecological harm because we would be damaging the ocean floor without changing the amount of destruction caused by terrestrial mining. (I’m ignoring second-order effects from lower greenhouse gas emissions due to lower prices of clean energy products, as currently direct killing and habitat destruction are much bigger contributors to wildlife loss than is climate change.)
The best paper I found on this question is “Energy Transition Metals: Bottleneck for Net-Zero Emissions?” by Lukas Boer, Andrea Pescatori, and Martin Stuermer. I like this paper because it estimates long-run (20-year) supply elasticities in addition to short-run (same-year) elasticities. Avoiding new terrestrial mines would be a big part of the ecological benefit of nodule collection, because this extensive margin is where a lot of the harm from terrestrial mining occurs. Increasing output from an existing mine may for example cause more pollution, but it wouldn’t result in the total land clearing and new infrastructure building that would come with a new mine.
Boer et al. estimate long-run supply elasticities of about 0.8 for copper and cobalt and an elasticity of about 1.5 for nickel (Figure 3). The short-run elasticities are about half as large, reflecting producers’ greater ability to increase output from existing or new mines in the long-run.
Comparing marine harms to terrestrial harms avoided
So am I right? The second question is whether the substitution of refined metals from land with those from the seabed would benefit wildlife. At a high level, the calculation is simple: compare the marine harms per ton of refined metal to the terrestrial harms avoided.
For terrestrial mining, the basic calculation could be: mining-affected area per ton of refined metal times the biodiversity value of the affected land. Biodiversity value could measure how much habitat loss in a particular location raises each species’ expected extinction risk, summed over species. Of course, whether all species' existence should be weighted equally is an open question, and there are measures of biodiversity value beyond extinction risk that could be considered instead.
One terrestrial data source is LIFE, which contains estimates of the marginal extinction impact of converting natural habitat. A researcher could predict the terrestrial area displaced by nodule supply, overlay that area on LIFE, and sum the values.
For nodules, the same logic applies, but there are two marine harms that would be added together. The first is benthic harm: the collector removes nodules and surrounding sediment, directly disturbing the seabed and destroying habitat used by seabed-dwelling organisms. The second is plume harm: after processing the nodules, the vessel pumps waste sediment back into the ocean. This may crowd out the nutritious particles eaten by filter feeders, reducing their abundance and affecting the larger animals that eat them.
The hardest part of the exercise is assigning biodiversity values to the affected marine areas. The main region of interest is the Clarion-Clipperton Zone (CCZ), a vast area of the Pacific Ocean between Hawaii and Mexico. An extinction-risk metric like LIFE does not seem to already exist for the CCZ. Possible starting points include the International Seabed Authority’s DeepData database and the CCZ species checklist. These datasets could be combined with judgements about species’ geographic ranges to produce expected extinction impacts of nodule collection
A first-pass comparison seems possible. Alternatively, one could perform the terrestrial computation only as a bounding exercise: how bad would nodule collection have to be for it to be a net harm to biodiversity? There would be some necessarily strong assumptions, but I think the existing estimates and datasets may be sufficient to produce a preliminary comparison or a bound. This would add important and currently missing evidence to inform the debate regarding whether to permit nodule collection from the CCZ.
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