An environmental catastrophe with greater economic impact than the global financial crash is occurring on the high seas, according to David Miliband. The former foreign secretary is to lead a new, high-level international effort to end the lawlessness of the oceans, which will be unveiled this week.

The high seas, which lie beyond any national jurisdiction, cover almost half the Earth's surface and decades of over-exploitation have caused trillions of dollars' worth of fish catches to be lost. Pirate fishing, often using slave labour and linked to cocaine and weapons smuggling, is rife and the damage caused to life in the oceans is harming the habitability of the whole planet. Future risks include sea-floor mining and rogue geoengineering.

"The worst of the current system is plunder and pillage on a massive scale," Miliband told the Observer. "It is the ecological equivalent of the financial crisis. The long-term costs of the mismanagement of our oceans are at least as great as long-term costs of the mismanagement of the financial system. We are living as if there are three or four planets instead of one, and you can't get away with that."

Miliband, in an unpaid role, will lead the new Global Ocean Commission, along with Nelson Mandela's former finance minister, Trevor Manuel, and the former president of Costa Rica, José María Figueres. The launch in London on Tuesday will introduce further commissioners, including more former heads of state and senior ministers from leading G20 nations.

"We are coming to a crunch time: 2014 needs to be the year when we reverse the degradation of the high seas," said Miliband, referring to the deadline set at the UN's Earth Summit in 2012 for the first ever laws to protect biodiversity in the open oceans.

Miliband knows from personal experience the difficulty of the task. In 2009, as foreign secretary, he established the world's biggest marine reserve in which no fishing is allowed: more than 640,000 square kilometres around the Chagos archipelago in the Indian ocean. However, last month a bitterly fought legal challenge from Mauritius was allowed to proceed at the international court of arbitration in The Hague.

Professor Callum Roberts, a marine biologist at the University of York, said protection for the open oceans was desperately needed: "The high seas are the last and most neglected of all natural spaces. They are home to some extraordinary species, for example, the leatherback turtle. It comes from a lineage 100m years old, but has declined by 95% in the last 20-30 years due to our depredations. Dolphins and sharks are in freefall.

"The oceans make up 95% of the living space on the planet and what happens there is extremely important for the habitability of our planet, from oxygen production to dealing with carbon dioxide and other pollution. Our impact means the oceans will do that less well, with serious consequences for humanity."

Miliband said: He said the seniority of the people leading the new commission was "really impressive" and pointed to the achievements of an analogous commission in the United States that successfully worked with the federal government to improve protection in American waters.

"We are going to try to fashion practical solutions that are an environmental win and an economic win, and with a commission which is avowedly across north-south, east-west, rich-poor divides."

He noted that the destruction of fisheries by over-exploitation costs $50bn (£32bn) a year in lost catches, according to the World Bank, totalling $1.5tn over the past three decades. This damages the livelihoods of the 200 million people supported by fishing, of whom 90% live in poor, developing countries.

A billion people already rely on fish as their key source of food, but catches are falling. With the global population expected to swell by three billion in coming decades, stocks must be allowed to recover to allow even greater catches to be sustainably harvested in future. Three-quarters of global fish stocks are already overfished or on the brink of being so, according to the UN's Food and Agriculture Organisation; not just well-publicised species such as tuna, but also many of the top 10 biggest fisheries, including Pacific anchovy, Alaskan pollock and Atlantic herring.

Pirate fishing is also a major issue, estimated to account for one-fifth of the global total market, worth $10bn-$23bn a year. The UN's Office on Drugs and Crime found that international fishing operators exploited corrupt systems even in nationally controlled waters. It also found that international gangs, often smuggling cocaine and weapons, had plundered valuable fish and often committed human rights abuses. The slave labour they use, sometimes children, are held as de facto prisoners of the sea, and deaths and severe physical and sexual abuse have been reported.

The governance of international waters – via the UN's 30-year-old laws of the seas, drafted to encourage exploitation – is dismissed as a "tragedy" by Miliband: "The current enforcement on the high seas is inadequate at best and worthless at worst." Roberts dubs the laws as "useless" and said that, when they were written in the 1970s, "people thought the resources of the oceans were limitless". Even so, the US has never ratified the treaty, deeply undermining its authority, while territorial disputes over the Arctic and Southern oceans rage on.

"The high seas were protected for thousands of years because people simply could not get there," said Miliband. "Exploitation has increased over 30 years, but the governance framework has not kept up." For example, there is no international mechanism at all for protecting biodiversity in the deep oceans.

New laws will also have to anticipate the growth of deep-sea mining for metals and potentially the dumping of tonnes of iron or minerals in the oceans in a bid to halt climate change – so-called geoengineering, Miliband said. In 2012, a 10,000 sq km geoengineering test took place off Canada without any authorisation.

"But enforcement in the modern world is not going to be a great new navy of ships polluting their way around the high seas," said Miliband. Satellite monitoring could be one solution, while another would be to force fishing vessels to carry location beacons at all times, as many merchant vessels already do.