Paulikas, and 3 co-authors, reported in early 2020 that A new, abundant, and high-grade polymetallic source of metals for the clean-energy transition could come on-stream in the next few years. The International Seabed Authority (ISA), established pursuant to the United Nations Convention on the Law of the Sea (UNCLOS), has awarded over a dozen exploration contracts for the collection of deep-sea polymetallic nodules from the Clarion Clipperton Zone (CCZ) and is now poised to adopt regulations for commercial exploitation (in ISA, 2019).
The potential commencement of deep-sea mining (DSM) of nodules has been met with opposition from Greenpeace and other NGOs concerned about biodiversity loss and ecosystem and carbon-cycle disruptions in the ocean (Greenpeace, 2019). To date, this DSM debate has narrowly focused on ocean impacts from the nodule-collection phase, whereas direct and indirect planetary-scale impacts and full life cycle impacts of production including onshore processing have been largely absent from consideration. Nor have the impacts of nodule collection been compared to current practice: using conventional metal-bearing ores on land to supply primary metal demand.
In the short-to-medium term, the bulk of new metal demand resulting from a metal-intensive clean-energy transition, population growth, and development will not be compressible, nor can this demand be supplied by recycling efforts alone (Hund et al., 2020). Until sufficient metal stocks are built up in the global system, a primary metal source is required to meet the new demand. Which primary metal source would create the least damage to the planet and its people: land ores or deep-sea polymetallic nodules? A comparative life cycle assessment (LCA) grounded in a planetary perspective is needed to answer this question and to help inform discourse on the consequences of entering the deep sea.
The authors begin to address these gaps. It follows established LCA methods to extend the current analysis of metal production to the CCZ nodule resource. LCA is a widely used, ISO-based scientific methodology for assessing comparative environmental impacts. It considers the direct and indirect contributions from materials, energy, transport, and other process inputs to compute an aggregate impact for a number of standardized indicators. Taking the consumption unit as a given so that any behavioral shifts, crowding-out effects, or policy externalities are isolated from study (Yang, 2017), a “cradle-to-gate” (from resource to refined metal) LCA enables a direct, apples-to-apples impact comparison of producing the same material from two different sources.
Given the urgency of the climate crisis, this paper quantifies impacts on climate change: it shares the results of the first cradle-to-gate LCA of metal production from polymetallic nodules with a focus on global warming potential (GWP) and carbon-sequestration cycle impacts, and compares them to land-ore mining. Several types of metal-bearing deposits have been explored in the deep sea-floor massive sulfides, cobalt crusts, seabed sediments, and polymetallic nodules with a unique environmental and economic footprint. Polymetallic nodules are of particular interest because they (1) occur in or on soft seabed sediment, unattached to the ocean floor, and can be collected without destructive rock cutting (Secretariat of the Pacific Community, 2013); (2) contain high-to-medium grades of four metals in a single ore and do not contain toxic levels of heavy elements (Haynes et al., 1985); (3) have metal contents serendipitously aligned with the metal needs of electric vehicle (EV) battery and assembly manufactured nickel, cobalt, manganese, and copper (AMY, 2018); and (4) are present in vast enough quantities within the surveyed CCZ to become a major source of battery metals for the coming decades.
The CCZ represents 1.5% of the world’s abyssal plains and hosts on its surface 34 billion wet metric tons of nodules containing 6 billion tons of manganese, 270 million tons of nickel, 234 million tons of copper, and 46 million tons of cobalt (Morgan, 2000). Allowing for protected areas and process inefficiencies, if half of these nodules were collected, the total commercial value of contained metals would be around 5 trillion US dollars (USD), based on average long-term projected commodity prices (AMC Consultants, 2019a).
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