Deep-sea mining: Superficial riches, deep hidden costs

Abstract Deep-sea mining (DSM) is promoted as a solution to secure minerals critical for a rapid energy transition¹,², yet its full economic, environmental, and social implications remain poorly quantified³–⁵. Here, we conduct arguably the most comprehensive cost-benefit analysis (CBA) of DSM to date, compiling and using data from publicly available articles simply yet powerfully. We estimate the net present value (NPV) of extracting 3 million dry tonnes of polymetallic nodules annually⁶,⁷, over 50-years, applying both conventional and intergenerational discounting to capture long-term impacts⁸–¹⁰. Using the average of reported metal prices, our study suggests that DSM could generate direct financial gains of ~USD12 billion over 50 years (i.e., ~USD240 million a year), non-financial costs are significantly higher —reaching ~USD68 billion (i.e., trading off USD5.6 of non-financial losses for USD1 of financial gain), and ~USD105 billion (trading off USD8.7 for USD1 of financial gain) under conventional and intergenerational discounting, respectively. Sensitivity analysis reveals that a 42% fall in mineral prices or an 85% extraction costs overrun, both plausible, would wipe out all projected financial gains. Even if the cost of extracting deep-sea minerals was zero, the NPV would still be negative. These findings highlight the economic flimsiness of DSM, reinforcing ecological and social concerns¹¹–¹³. Given that DSM’s net value is negative, policymakers should strengthen existing mining practices and prioritize circular economy strategies over high-risk exploitation¹⁴.