The legally binding accord outlines rules to protect biodiversity in waters outside national boundaries.

On Monday, UN Secretary-General Antonio Guterres hailed as a “historic achievement” the pact that will establish a legal framework to extend environmental protections to international waters, known as the high seas, which cover more than 60 percent of the earth’s surface.

Climate change is disrupting weather patterns and ocean currents, raising sea temperatures, “and altering marine ecosystems and the species living there”, Guterres said, adding that marine biodiversity “is under attack from overfishing, over-exploitation and ocean acidification”.

“Over one-third of fish stocks are being harvested at unsustainable levels,” the UN chief said. “And we are polluting our coastal waters with chemicals, plastics and human waste.”

Scientists have increasingly come to realise the importance of oceans, which produce most of the oxygen we breathe, limit climate change by absorbing CO2, and host rich areas of biodiversity, often at the microscopic level.

But with so much of the world’s oceans lying outside individual countries’ exclusive economic zones, and thus the jurisdiction of any single state, providing protection for the so-called “high seas” requires international cooperation.

UN member states finally agreed on the text for the treaty in March, and Guterres urged all countries to spare no efforts to ensure that it is signed and ratified as soon as possible.

Officially known as the Treaty on Biodiversity Beyond National Jurisdiction, it falls under the UN Convention on the Law of the Sea, which came into force in 1994.

It will be opened for signatures on September 20, during the annual meeting of world leaders at the UN General Assembly, and it will take effect once it is ratified by 60 countries.

The accord also establishes ground rules for conducting environmental impact assessments for commercial activities in the oceans.

Such activities, while not listed in the text, would include anything from fishing and maritime transport to more controversial pursuits, like deep-sea mining or even geo-engineering programmes aimed at fighting global warming.

A key tool in the treaty will be the ability to create protected marine areas in international waters. Currently, only about one percent of the high seas are protected by any sort of conservation measures.

The treaty also establishes principles for sharing the benefits of “marine genetic resources” (MGR) collected by scientific research in international waters – a sticking point that almost derailed last-minute negotiations in March.

Developing countries, which often don’t have the money to finance such expeditions, fought for benefit-sharing rights, hoping to not get left behind by what many see as a huge future market in the commercialisation of MGR, especially by pharmaceutical and cosmetic companies searching for “miracle molecules”.