Q&A: What does deep-sea mining mean for climate change and biodiversity loss?

The deep sea has emerged as a new mining frontier in the global race towards energy security, with countries vying to explore and exploit its reserves of metals, such as nickel, copper, cobalt and manganese.

These minerals – critical to the energy transition – are held in the deep ocean’s nodules, hydrothermal vents and crusts, but the impacts of mining these deposits are still far from being fully understood.

In 2021, the Pacific island state of Nauru triggered a legal process for countries to agree rules around mining the seabed, or – in their absence – allow commercial mining of the deep sea to begin by 2025.

Since then, 31 countries have called for some form of a ban, moratorium or pause on deep sea mining in international waters until its impacts on the ocean, climate and biodiversity are properly investigated.

Companies, such as BMW, Volvo and Renault, have joined this groundswell and are increasingly distancing themselves from deep-sea mining, along with banks such as Credit Suisse, ABN Amro and the European Investment Bank.

At the same time, 20 countries already hold 30 exploration contracts in areas beyond national boundaries, while countries such as Norway have supported deep-sea mining in their domestic waters.

As the International Seabed Authority meets in Kingston, Jamaica for another round of critical talks on deep-sea mining, Carbon Brief unpacks what mining could mean for climate change and biodiversity.

• What is deep-sea mining?
• What is the state of deep-sea mining around the world?
• What does deep-sea mining mean for climate change?
• How does it impact global marine biodiversity and coastal communities?

What is deep-sea mining?

The first successful test of deep-sea mining technology occurred in 1970 off the coast of the US state of Georgia.

While the technology was deemed not to be commercially viable at the time, interest in deep-sea mining has been renewed in recent years, with nearly two dozen companies currently holding exploration contracts.

Jiaolong, China’s crewed submersible about to dive into the South China Sea. Jiaolong discovered a collection of polymetallic nodules in Puyuan Seamount in the South China Sea. Credit: Xinhua /Alamy Stock Photo.

The “deep” seabed is defined as the seafloor at ocean depths greater than 200 metres – comprising about two-thirds of the world’s total seabed.

Companies looking to mine in the deep sea are typically seeking rare-earth elements, such as cobalt and platinum, in three forms: polymetallic nodules, polymetallic sulphides and cobalt-rich ferromanganese crusts.

A polymetallic nodule. Image: Parent Géry (2021)

Polymetallic nodules are small lumps of minerals and metals that are found on the abyssal seafloor – the vast plains of the ocean depths found between four and six kilometres (km) beneath the ocean surface.

Polymetallic sulphides form near hydrothermal vents, as a result of superheated water that extracts sulphur and metal from the ocean crust. They are primarily found along mid-ocean ridges and in volcanic regions, and are estimated to contain around 30m tonnes of copper and zinc.

Ferromanganese crusts are also found in regions of high volcanic activity, but since they are found at shallower depths, they often occur in countries’ national waters. They are rich in cobalt and platinum, among other rare-earth elements.

The periodic table below shows the major elements that companies are hoping to exploit from nodules and crusts on the seafloor.

A list of key critical minerals discovered in the deep sea, highlighted in the periodic table. Sources: International Seabed Authority (2024), Miller et al. (2018), Ohta et al. (2021), International Energy Agency (2021), International Renewable Energy Agency (2022). Graphic: Carbon Brief

Proponents of deep-sea mining argue that the metals found in the deep sea are necessary for achieving the transition away from fossil fuels. (See: What does deep-sea mining mean for climate change?)

But many scientists and conservation organisations say that the potential impacts on climate and deep-sea biodiversity are too poorly understood for mining to proceed. (See: How does it impact marine biodiversity?)

Currently, polymetallic nodules are the main focus of most deep-sea mining exploration contracts – more than a dozen countries hold such contracts. Collecting nodules from the seafloor involves a tractor-like machine that ploughs the seabed and separates the nodules from the surrounding sediment. The nodules are piped back up to the surface, while the sediment is released back into the ocean.

The chart below shows the number of exploration contracts held by each country and company.

Exploration contracts granted by the International Seabed Authority (ISA) to countries and companies, grouped by their sponsoring states. In all, the ISA has issued 30 contracts to 21 contractors across 20 countries. The Interoceanmetal Joint Organisation has 6 sponsoring states: Bulgaria, Cuba, Czech Republic, Poland, Russia and Slovakia. Source: International Seabed Authority Secretary-General Annual Report (2023). Graphic: Carbon Brief.

Nodules are ubiquitous throughout the world’s oceans, but the places where mining is commercially viable – where the nodules occur in high enough density to be worth the expense of extraction – are more limited.

The area with the highest concentration of nodules is the Clarion-Clipperton Zone (CCZ), a region of the Pacific located between Hawaii and Mexico. By conservative estimates, the CCZ holds more than 21bn tonnes of nodules. Currently, the ISA has granted exploration contracts within the CCZ to 16 countries, including the UK.

Other regions that have attracted significant commercial interest are the mid-Atlantic Ridge, which runs through the centre of the Atlantic Ocean, the north-west Pacific Ocean and the Indian Ocean. These three regions represent 11 exploration contracts in total. (See: What is the state of deep-sea mining around the world?)

The map below shows where these contracts are concentrated and their sponsoring states.

A map of deep-sea mining exploration areas and reserved areas (red dots representing each exploration contract), the deep sea mineral resources they are for – polymetallic nodules (green), polymetallic sulphides (blue) and cobalt-rich ferromanganese crusts (pink) – and key regions slated for extraction in the deep ocean. Source: International Seabed Authority exploration contracts and Carbon Brief analysis. Graphic: Carbon Brief

What is the state of deep-sea mining around the world?

The UN Convention on the Law of the Sea (UNCLOS) is an international treaty that provides a framework to regulate the use of the world’s seas and oceans.

It came into force in 1994, but traces its origins to a 1967 impassioned speech by the ambassador of Malta, Arvid Pardo. In it, Pardo called for “an effective international regime” that recognised the seabed and ocean floor as “the common heritage of humankind”, with financial benefits from the oceans flowing first to poorer countries.

Among other bodies and orders, UNCLOS established the International Seabed Authority (ISA), which is based in Kingston, Jamaica, and controls all resource extraction in the deep sea.

By default, all 169 countries and the EU that are party to UNCLOS are members of the seabed authority, with each member allowed one representative and one vote.

While Russia, Japan, China and South Korea were granted permits to explore the Pacific for polymetallic nodules as early as 2001, the ISA’s deliberations and workings have been under greater scrutiny in recent years, becoming the subject of frontpage news and late-night comedy segments in recent years.

This heightened attention in the media has been driven both by a global race for critical minerals and a ticking deadline to frame mining rules or risk countries proceeding without them.

In 2021, the island-state of Nauru triggered the ISA’s “two-year rule”, which allows a mining plan to be principally approved within two years, even while draft regulations for mineral exploitation are still on the drawing board.

However, the July 2023 deadline came and went with no mining code approved.

There is a growing chorus of 31 governments – led by Palau, Fiji, Samoa and the Federated States of Micronesia – that have called for some form of ban, moratorium or pause on deep-sea mining until its ecological impacts are better understood.

Dutch band “The Polymetallic Nodules” performing at a deep-sea mining protest in Canary Wharf, London. Credit: Eleventh Hour Photography /Alamy Stock Photo.

Some governments have voted to ban the practice in their own domestic waters, including the Australian state of New South Wales, the south Pacific islands of New Caledonia and several US states and territories.

But other states are still in favour of deep-sea mining, including India, China and Norway. Earlier this year, Norway passed a law approving deep-sea mining in its domestic waters.

The table below lists ISA sponsoring states and sub-regions, the number of exploration permits they currently possess and their positions in support or opposition to deep-sea mining.

On 15 July, the ISA resumed its 29th annual session in Kingston. On the agenda was trying to settle the debate over the mining regulations and electing a new secretary general for the next four years.

Additionally, for the first time, the assembly was to discuss a proposal by Chile and other governments for a general policy to protect and preserve the marine environment, which could act as a failsafe in the absence of mining rules or a moratorium.

According to international environmental lawyer Duncan Currie, countries are “a long way away from being able to get anywhere near [mining] rules that people consider could be adopted”. He tells Carbon Brief:

“I think most delegations accept that the regulations won’t be ready for adoption this time next year [July 2025]; I think there’s really close to a zero chance. But what will they do when Nauru puts forward a [mining] plan of work at the end of the year? Will they just talk for another year? Will they change the way they operate? What is done with that application is a very big question.”

Additionally, while there has been progress on acknowledging “underwater cultural heritage”, Indigenous groups are pushing much harder for free, prior and informed consent in deep-sea mining projects, as well as for real participation in the ISA.

Solomon “Uncle Sol” Kaho‘ohalahala reads the Hawaiian Kumulipo creation chant ahead of the debate on underwater cultural heritage. Image: Diego Noguera, IISD/ENB (2024)

The ISA is also not the only international policy that determines the future of the deep sea and life within it. In March 2023, nations agreed to a new high seas treaty” governing the conservation of biodiversity in international waters.

The high seas treaty has extensive norms around conducting environmental impact assessments (EIAs) for deep-sea impacts, including assessing cumulative impacts, but it does not directly govern seabed activity. The ISA currently only has non-binding recommendations on EIAs for exploration, while its EIA regulations for exploitation are still in draft form.

Countries have called for “meaningful and enhanced cooperation and collaboration” across international agreements, but it is still unclear how the ISA and the high seas treaty will work together.

What does deep-sea mining mean for climate change?

To date, the extraction of polymetallic nodules has largely been – in the words of the Geological Society – “uneconomic”. Nonetheless, the deep sea has been increasingly seen as a source of critical minerals necessary to meet global climate goals.

In a 2021 report covered by Carbon Brief, the International Energy Agency (IEA) estimated that the production of minerals critical to clean energy technologies, such as batteries, may need to quadruple over the next two decades to achieve the Paris Agreement warming limit of “well below” 2C – or to expand by as much as six times to reach net-zero globally by 2050.

Today’s mineral supply and investments “fall short” of what a rapid transition will need, according to the report.

While many deep-sea minerals, such as nickel and manganese, are abundant on land, they are also concentrated within specific climate and biodiversity-critical regions. And deforestation and rights abuses – from child labour to forced evictions – have been extensively reported in mining areas.

A nickel mine in Soroako, Indonesia. Credit: Sipa USA /Alamy Stock Photo.

However, the impacts of deep-sea mining on climate are still a subject of scientific and political debate.

One 2020 study, for instance, estimated that making one billion EV batteries from nodules could reduce atmospheric CO2 by 11.5bn tonnes of CO2-equivalent and said that nodules “put 94% less sequestered carbon at risk” than land-based mining would.

Another 2020 study, however, stated that “scientific misconceptions are likely leading to miscalculations of the environmental impacts of deep-seabed mining”. It added that the disturbance from a single mining operation “could easily be” up to four times larger than its direct mining footprint, affecting up to 32,000 square kilometres over 20 years.

The potential cost of restoring damage to deep-sea ecosystems could be “astronomical”, according to a report by Planet Tracker, a not-for-profit thinktank.

A 2022 UN Environment Programme Finance Initiative (UNEPFI) briefing paper, meanwhile, saw “no foreseeable way” in which the financing of deep-sea mining could be consistent with a sustainable blue economy. It called on investors to instead “focus efforts” on reducing “the environmental footprint of terrestrial mining” and “support the transition toward a circular economy” to make current mineral demand “obsolete”.

A 2023 study found that deep-sea mining “is unlikely to resolve the sustainability challenges in the conventional mining sector” and any environmental impacts avoided on land “would be at the expense of economic benefits in mining-reliant” developing countries.

At the same time, “next generation” batteries that do not use cobalt, nickel and manganese are seeing rising investment from manufacturers, potentially reducing the future need for these metals.

So far, BMW, Renault, Volkswagen, Volvo and Scania are among the many automotive companies that have supported a moratorium on deep-sea minerals in their supply chains. While General Motors and Tesla are both exploring low- or no-cobalt batteries, shareholders of both companies voted against proposals to agree to a moratorium on sourcing deep-sea minerals for their EV battery systems.

Deep-sea mining can also harm marine organisms that are crucial for climate regulation – those that store carbon in the seabed or produce oxygen in the deep ocean.

Microbes and zooplankton, for instance, play a “crucial role in particulate organic carbon degradation”. However, biodiversity in the deep sea “is still poorly characterised”.

Diego Lillo Goffreri, an attorney in the ecosystems programme at the Interamerican Association for Environmental Defense (AIDA) and Latin America regional coordinator for the Deep Sea Conservation Coalition (DSCC), tells Carbon Brief:

“These studies conclude that removing the sedimentary layer [of the ocean floor] will mean the loss of absorption capacity and the reincorporation of CO2 into the marine environment.”

Aside from sequestering carbon, the deep sea may be relevant for oxygen production.

A 2024 study found that polymetallic nodules may be responsible for producing oxygen at the seafloor in the CCZ. The authors said that this oxygen production could be critical for sustaining life at the seafloor.

Goffreri says that the new discovery significantly changes the cost-benefit analysis of deep-sea mining. He adds:

“Is economic value more important than oxygen production? It’s a finding that should be a game-changer.”

Canada’s The Metals Company, which partially funded the research, “attempted to poke holes in the study”, according to E\&E News, but researchers stood by their findings. Duncan Currie, an international environmental lawyer with the Deep Sea Conservation Coalition, tells Carbon Brief:

“It was a real concern that The Metals Company was adopting the position of questioning that Exxon has taken on questioning [peer-reviewed] climate science and saying ‘we’re going to be doing our own research’.

“Will [they] hold off on filing [mining] applications until their own research is published? They didn’t answer the question, but it’s a really important [one] because the science out there is saying there’s totally new mind-blowing discoveries being made.”

The Metals Company has said it is “preparing a comprehensive rebuttal to contribute to the scientific literature” and is “committed to scientific integrity and transparency, and will continue to provide accurate, peer-reviewed research to enhance our understanding of the deep sea”.

How does it impact global marine biodiversity and coastal communities?

Once thought to be barren and lifeless, the seafloor is home to an extraordinary and delicate variety of life that is potentially vulnerable to mineral mining.

Seafloor communities at water depths of 3,000 to 6,000 metres span more than 60% of Earth’s surface.

For researchers to access the deep ocean and assess the impacts of deep-sea mining is “really tricky”, says Dr Kerstin Kröger, a deep-sea ecologist advising the UK government on impacts of human industrial activities in the deep sea.

The costs and difficulty of conducting research can be prohibitive, she tells Carbon Brief:

“It’s a massive undertaking. In my opinion, we still do not have sufficient scientific evidence to really understand the risks of deep-sea mining. We need this to responsibly exploit these mineral resources.”

Despite this, scientists have already warned about the “inevitable” and “very likely irreversible” loss of biodiversity, according to the National Committee of the Netherlands of the International Union for Conservation of Nature (IUCN).

A 2020 opinion article by a diverse group of marine scientists and published by PNAS argues that deep-sea mining could also pose “significant risks” to deep midwater ecosystems, which extend from depths of 200 metres to 5km and connect shallow and deep-sea ecosystems. It states that mining would disturb both biodiversity and ecosystem services, including carbon export, nutrient regeneration and fish stocks.

The figure below illustrates the ore extraction process on the seafloor and its potential effects on marine biodiversity.

Potential impacts of deep-sea mining on marine ecosystems. Graphic: Carbon Brief based on Drazen et al. (2020).

Seafloor mining vehicles emit noise and plumes of sediments that may impact organisms who live in the midwaters, from reducing their ability to communicate and causing physiological stress, to forcing species to migrate and causing changes in community composition.

The PNAS article listed a range of species that could potentially be affected by these effects, including sharks, dolphins, whales. Other animal biodiversity inhabiting the midwaters includes squid, fish, shrimp, copepods and jellyfish.

Flying spaghetti monster (Bathyphysa conifera) in the deep sea. Credit: Adisha Pramod / Alamy Stock Photo.

As scientists have explored the deep ocean, they have observed countless other species living on the seafloor that would also be affected by deep-sea mining. A 2023 study found that the CCZ is home to more than 5,000 unnamed species and that roughly 90% of species that live in the fracture zone are unknown to science.

In addition, the small organisms living in the seafloor sediments are believed to contribute to ecosystem processes, such as nutrient cycling and degradation of organic pollutants.

As collector vehicles remove polymetallic nodules from the seabed, they will also extract and compact the surface layer of these soft sediments, according to a 2021 study.

Goffreri, from AIDA, tells Carbon Brief that very little is known about the species that inhabit polymetallic nodules themselves. He says that “the first risk is to lose biodiversity that is under-studied”, adding that such organisms could have economic value in the pharmaceutical or other industries.

Krogër adds that in the deep sea, animals, bacteria, virus and fungi are not adapted to ecosystem changes, since temperature and pressure there are quite steady compared to terrestrial ecosystems. This makes deep-sea organisms particularly vulnerable to disturbances.

She says that the world should question if it really needs more minerals and whether it is worth the destruction of extracting them from valuable ecosystems. Instead, she says, improvements should be made towards recycling batteries and the world should move to a more circular economy.

She tells Carbon Brief:

We need to recycle much more and to become much smarter about what we use for which purpose, and not just make and use things because we can.”