Mining the deep seabed for critical minerals features prominently in 20th century international agreements, yet it’s only now that commercial exploitation approaches. Technological progress and demand for metals for the clean energy transition enable this. The deep seabed is one of Earth’s most pristine habitats, and our limited understanding of its ecosystems fuels vociferous opposition to mining. How can you destroy what you don’t even know? But foregoing deep-sea mining has opportunity costs, like higher prices slowing electrification. And the less we mine at sea, the more we likely mine on land—which has large, well-known harms. To make progress on this trade-off, let’s compare the most advanced form of seabed mining to its land-based counterpart, focusing on nickel as our running example.
The first type of commercial seabed mining could be the collection of polymetallic nodules: golf-ball-sized lumps rich in nickel (and cobalt and manganese). These nodules litter the abyssal plain—seafloor more than three kilometers below the ocean’s surface—of the Clarion Clipperton Zone, between Hawaii and Mexico. Collector vehicles can suck the nodules from the top of the seafloor, then send them up to the surface through a vertical pipeline. By comparison, the most common form of existing nickel mining is “open-pit” in Indonesia, which involves clearing tracts of rainforest and digging massive holes to access the ore beneath. The waste soil, rock, and water are dumped in piles, tailing ponds, or in the ocean.
Habitat destruction and direct killing are the leading causes of species extinction (climate change is much less important, at least so far). Collection of polymetallic nodules from the abyssal plain would likely destroy less habitat than open-pit mining on land. And some of the most ecologically important areas of the Clarion Clipperton Zone have already been excluded from potential seabed mining; seabed miners would also be required to leave some fraction of their tracts untouched. Because the abyssal plain is relatively uniform, these non-mined areas may host many of the same species as mining zones, potentially providing refuges from mining-induced extinction. Finally, the abundance and diversity of species per square km is likely much less than in the Indonesian rainforest. Put together, we’re probably looking at less area damaged, and less damage per unit area. (Other forms of deep-sea mining, like on hydrothermal vents, could be more destructive than polymetallic nodule collection, but probably still less so than clearcutting tropical rainforests.)
The main pollutant from nodule collection would likely be the sediment plumes stirred up by collector vehicles as they traverse the abyssal plain and separate nodules from sediment. One experiment found that most disturbed sediment stayed near the seafloor, spreading horizontally rather than rising higher in the water column where it could affect midwater species. Nodule collection would also cause some noise and light pollution, affecting deep-sea species adapted to silence and darkness. By contrast, the water, soil, and air pollution from open-pit nickel mining are all known to be severe. People live near open-pit mines in Indonesia, but no one lives on the abyssal plain. If you’re interested in human health, this is a big advantage of seabed mining! Finally, this lifecycle assessment calculates that greenhouse gas emissions from seabed nodule collection are an order of magnitude lower than land-based mining.
Natural resources in the Clarion Clipperton Zone are designated the “common heritage” of humanity under the United Nations Convention on the Law of the Sea. That means their royalties would be divided among the 169 member countries of the International Seabed Authority (ISA). While the ISA has yet to decide the royalty sharing formula, one think tank predicts the average country would receive modest annual payments, in the range of single-digit millions. Countries like Nauru that sponsor private mining companies could earn hundreds of millions per year.
Employment in seabed mining would be lower and more specialized than the demand for unskilled labor generated by open-pit mines. Developing countries could dedicate their royalty payments to training citizens for seabed mining, and require through the ISA minimum employment quotas. But there’s no analogue to the structural transformation of a large country that Indonesia is trying to engineer with its nickel processing industry. Processing adds more value than mining, but it has distinct environmental damages. Where minerals like nickel are processed and recycled seems more important for jobs than the mining stage itself.
The precautionary principle advises inaction when uncertainty is high—and uncertain we remain about deep-sea ecosystems. Adherence to this principle explains some opposition to deep-sea mining in my view. But inaction is also a choice: for known harms from land-based mining and commodity prices that leave greenhouse gas emissions higher for longer. Economists could contribute valuable research to this frontier topic, including: cost-benefit analyses considering what we do know about proposed deep-sea mining impacts; modeling that recognizes the substitutability of deep seabed and land-based mining; and how developing countries can maximize economic benefits from deep-sea mining.
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