Speaking ahead of the UN Ocean Conference (UNOC) in Nice, the celebrated broadcaster and environmentalist said the degradation of the deep sea would provoke global outrage if it occurred on land.

"What we've done to the deep ocean floor is just unspeakably awful," he said. "If you did anything remotely like it on land, there would be an uproar."

The remarks come as world leaders, scientists, and NGOs gather to assess the state of the oceans amid accelerating threats from climate change, plastic pollution, overfishing and emerging industries such as deep-sea mining.

Pressure builds to ratify High Seas Treaty

A central objective of this week's summit is to galvanise support for the High Seas Treaty — a landmark agreement signed in 2023 that pledges to place 30% of the world's ocean under protection by 2030.

So far, only 32 countries have ratified the treaty; 60 are needed for it to come into effect. Environmental groups warn that progress is lagging, and marine protections remain weak and often poorly enforced.

Sir David's comments coincide with the premiere of his latest documentary Ocean, which highlights the devastating impact of bottom trawling and calls for urgent safeguards to preserve the ocean's capacity to absorb carbon and support biodiversity.

Marine protection undermined by destructive practices

While Marine Protected Areas (MPAs) are expanding on paper, many continue to allow destructive practices within their borders. In the UK, bottom trawling — which scrapes the seabed and devastates ecosystems — is still permitted in over 90% of MPAs, according to campaign group Oceana.

"We depend on the ocean in every possible way, but bottom trawling is destroying its foundations," said Dr Amanda Vincent, a professor of marine conservation at the University of British Columbia.

Parliamentary committees and scientists have repeatedly called for a ban on trawling in protected zones, warning that without such restrictions, protections are "little more than lines on a map."

Fishing industry representatives, however, argue that bottom trawling can be efficient if deployed in appropriate areas. Elspeth Macdonald, CEO of the Scottish Fishermen's Federation, told the BBC that the method is not inherently destructive unless misused.

Scientists counter that even selective restrictions can allow fish stocks to recover, benefitting ecosystems and long-term food security.

Climate crisis driving ocean collapse

Beyond fishing, climate change is placing unprecedented stress on marine life. The oceans have absorbed more than 90% of the excess heat generated by greenhouse gas emissions. Without that buffering effect, global surface temperatures would be dozens of degrees higher, scientists say.

"If the oceans hadn't absorbed the heat, the planet would be 36°C warmer — not 1.5," said Prof Callum Roberts of the University of Exeter. "We'd be living in Death Valley conditions."

That heat is already proving lethal for coral reefs, which have undergone mass bleaching and mortality events across the globe. Dr Jean-Pierre Gattuso, co-chair of the One Ocean Science Congress (OOSC), said coral systems could become the first major ecosystems to disappear entirely due to climate change.

Deep-sea mining: a flashpoint issue

Another flashpoint at the conference is deep-sea mining, a controversial practice that could open international waters to industrial extraction of minerals from the ocean floor.

The UN has struggled for over a decade to reach consensus on regulatory frameworks for the emerging sector. Despite that, former U.S. President Donald Trump signed an executive order in April permitting deep-sea mining in international waters — a move criticised by France and China as violating international norms.

Scientists are calling for a moratorium on deep-sea mining, citing a profound lack of knowledge about the ecosystems at risk.

"Deep-sea biology is the least understood and most threatened of all global ecosystems," said Prof Peter Haugan of the International Science Council. "We must apply the precautionary principle when science is lacking."

A call to act

The stakes for the UN Ocean Conference are high. The ocean regulates climate, feeds billions, generates trillions in economic value, and provides 80% of the oxygen we breathe. But its ability to perform these functions is being eroded by human activity.

"We need world leaders to understand that protecting the ocean is not just about whales and corals," Attenborough said. "It's about protecting the life systems that make this planet habitable."