Deep sea mining could be worse for the climate than land ores

Deep Sea Mining, Greenwashing

London 5 December: As decisions over the future viability of deep sea mining are under review, Planet Tracker’s latest report ‘The Climate Myth of Deep Sea Mining’ examines deep sea mining companies’ claim that mining polymetallic nodules could be a low carbon alternative to mining on land.

There are only three academic lifecycle assessment studies evaluating the ‘nodule-to-commodity’ climate impact of copper, cobalt, nickel and ferromanganese produced from polymetallic nodules and land ores.

Two of the three studies were funded by, and conducted in collaboration with, deep sea mining companies: one by The Metals Company (formerly DeepGreen Metals) and one by Global Sea Mineral Resources. The third paper, published by Fritz et al. in 2023, had no support from the deep sea mining industry.

Comparing these three studies underlines the huge variance in the estimated climate impacts of nodules and land ores. Depending on the choice of methodology, background data, software and assumptions and parameters used, deep sea nodules could have 28% higher or 76% lower climate impact than land ores. Planet Tracker believes that such a marked variation in results is not a good enough basis for making decisions about the future of deep sea mining.

Over 70% of greenhouse gas emissions for both land ores and deep sea nodules come from metallurgical processing, the energy- and fossil fuel-intensive processes that turn nodules and land ores into metal products. This means that climate impact is less dependent on whether metals come from the deep sea or from land and is more dependent on the properties of processing: mainly the sources of fuel and electricity used, process efficiency and processing technique.

Deep sea mining could have a long-term impact on ocean carbon stocks and sequestration services. Marine sediments are an important part of the global carbon cycle and make up the largest pool of sediment or soil carbon stocks in the world. While the rate of carbon sequestration is relatively slow at the deep seabed, ocean sediments can store carbon for millions of years if left undisturbed.

Planet Tracker estimates that deep sea mining vehicles kicking up sediment plumes could disturb 172.5 tonnes of carbon each year for every km2 mined. For context, only 13.9 kg of carbon per km2 is sequestered every year in the Clarion-Clipperton Zone where deep sea mining licenses have been granted.

Sediment plumes from deep sea mining machinery could impact carbon sequestration taking place in ocean waters by blocking sunlight and reducing photosynthesis. Carbon sequestration carried out by plants living on the nodules being mined would also be stopped completely. These impacts haven’t yet been calculated but considering that nodules take tens of millions of years to form, some of this damage would essentially be permanent.

“Through this research we really want to stress that deep sea mining could be a significant greenhouse gas emissions and contribute to climate change, which exposes financial institutions to policy, regulatory and reputational risks”, says Emma Amadi, Investment Analyst at Planet Tracker and one of the report’s authors.

“We want to encourage financial institutions to support a moratorium on deep sea mining  and we’d also encourage them to support the decarbonization of terrestrial mining and metals production, for example supporting the electrification of mining with renewable energy sources and supporting the development and scaling of low-carbon metal processing routes like hydrometallurgy which reduce or remove the need for fossil fuels”.

The Climate Myth of Deep Sea Mining can be downloaded  here.




For more information please contact:

Dominic Lyle, Planet Tracker | t: +44 7484 654 941