Time to protect all the high seas from all forms of resource extraction - forever

It's our job as scientists to consider an issue dispassionately and analytically. But sometimes, when the evidence warrants it, we also have to sound the alarm. Today we are doing just that, because the planet's largest single ecosystem - the international ocean - needs urgent protection, and if nothing is done it will soon be too late. 

The international high seas, which lie beyond the 200-nautical mile boundaries of national Exclusive Economic Zones, comprise 61% of the ocean, 43% of the planet's entire surface and two-thirds of its living space. While they have been cruelly exploited for whales in the past, and are increasingly being devastated by modern-day industrial fishing, new threats could now damage them beyond repair. 

While very little (under 6%) of the global fish catch comes from the high seas, industrial fishing by a small number of richer countries - often using highly subsidised fleets and with serious problems around slave labour and criminal activity - kills hundreds of thousands of seabirds like albatrosses, thousands of turtles and tens of millions of oceanic sharks, some of which are now critically endangered. So-called 'fish aggregation devices' deployed by tuna vessels expand this slaughter to manta rays, dolphins and juvenile fish, and pollute the ocean with immense quantities of plastic. 

Now a new threat has arisen. Deep-sea mining is being proposed as a source of critical minerals for the green transition, with over 30 active exploration contracts and calls for a start to commercial mining being pushed aggressively by some governments and private interests. This is unnecessary: more than sufficient metals reserves exist on land, in generally richer concentrations; these can be extracted with better oversight and far less ecological impact than thousands of metres down on the sea floor. 

It is also dangerous. Deep sea mining will disturb sediments laid down over millennia, releasing buried carbon and polluting the water column over thousands of cubic kilometres. Habitats for deep-sea life on polymetallic nodules and fragile sea mounts - themselves formed over millions of years - will be destroyed in minutes like rainforests being levelled by bulldozers. 

This is why, as world leaders convene this week at the UN Ocean Conference in Nice, France, we are putting forward a straightforward proposal: that the entire high seas should be protected from all forms of resource extraction, not just now but forever. In this way they could enjoy the same status as Antarctica, once also proposed for mining and other exploitation in ways that are now unthinkable. Antarctica is today recognised by all nations as a global commons to be fully protected forever - the same status is now needed for the high seas. 

The UN High Seas Treaty, agreed in 2023, represents the first serious attempt by the global community to better manage and protect high seas wildlife for the benefit of humanity. It is essential to the establishment of international marine protected areas that will enable the world to meet its commitment to protect 30% of the ocean by 2030. But 30% is not enough - it leaves two thirds of the high seas open to destruction, while the ratification of the Treaty could in any case take years.

It is also essential to realise just how critical the ocean is to the entire Earth system. Phytoplankton produce half of the oxygen that circulates on Earth each year, and the vast depths have so far taken up more than 90% of the excess heat trapped by greenhouse warming. The deep ocean is also the biggest and most secure carbon sink, with hundreds of billions of tonnes of carbon buried in seafloor sediments and taking up CO2 totalling 3 billion tonnes of carbon per year: without this vital service, the Earth might already be 3°C warmer than pre-industrial conditions.

Our proposal also accords with global justice. Currently most industrial high seas fishing is carried out by a small number of countries, including China, Spain, Taiwan, Japan, South Korea and Indonesia. If the high seas are left alone, there will be more fish available for fisheries in national waters spread across far more countries, especially in the Global South where seafood is important for nutrition and food security. 

It also accords with natural justice. We have hardly even begun to explore the high seas. Scientists regularly find entirely new species, from enormous squid to strangely shaped phosphorescent fish, in the vast ocean depths which are still largely unaffected by human disturbance. These are not just critical ecosystems - as David Attenborough portrays vividly in his film Ocean, they are amazing, awe-inspiring places and host extraordinary and diverse life forms that it is our duty to protect. 

And it is not yet too late. High seas fisheries are relatively unimportant economically or for food - much of the krill catch goes to pet food, for instance. Seabed mining has not yet begun. As a global commons, the high seas belong to us all, so we should all be involved in this crucial decision. 

As experts in ocean and climate science, we believe the science is now clear. Extractive use of the high seas is a threat not just to the creatures that live there but to all of us. Scientifically, we now know that the ocean, not the land is the fundamental determinant of the state of the planet. Currently, we are putting the stability of this critical ecosystem at grave risk. 

Instead, like the Antarctic continent, the ocean must be fully safeguarded in perpetuity. This is our once-only opportunity to save half the world, and in the process protect all life on Earth - including ourselves.

Callum Roberts is Professor of Marine Conservation at the Centre for Ecology and Conservation, University of Exeter and Chief Scientist of the Convex Seascape Survey.

Johan Rockström is Professor of Earth System Science and Director of the Potsdam Institute for Climate Impact Research (PIK) at the University of Potsdam, Germany, and is Chief Scientist at Conservation International.