By Virginia Furness

LONDON (Reuters) - While many countries have agreed to take steps to protect the vast, ungoverned swathes of the world's oceans, they have yet to see their High Seas Treaty go into effect. This week's U.N. Oceans Conference in the French city of Nice hopes to change that.

WHAT IS THE HIGH SEAS TREATY?

The treaty, signed in 2023, provides a legal framework for creating marine protected areas on the "high seas", or the ocean areas that lie beyond any national jurisdiction.

Currently, less than 3% of the oceans are under some form of protection, although altogether the world's oceans cover two-thirds of the planet.

The treaty contains 75 points covering areas such as protecting, caring for and ensuring responsible use of marine resources, and includes a provision for requiring environmental impact assessments of any economic activities in international waters.

The treaty also aims to ensure that all countries have fair and equitable access to the ocean's resources. While it is widely referred to as the High Seas Treaty, officially it is called the Biodiversity Beyond National Jurisdiction Treaty.

As of Monday, French President Emmanuel Macron said 50 countries had ratified the treaty, with 60 needed for it to go into effect.

Separate to the High Seas Treaty, countries agreed under a 2022 U.N. biodiversity pact to put 30% of their territorial waters under conservation.

WHY DO WE NEED AN OCEAN TREATY?

Oceans support coastal economies and livelihoods through tourism, fishing, shipping, mining, offshore energy and more.

Oceans also absorb about a third of the world's carbon dioxide, or CO2 - the primary gas driving climate change - while ocean-swimming phytoplankton provide about half of the world's oxygen.

But marine life is now struggling, and human industry and development are almost entirely to blame.

More than 1,500 ocean plants and animals are now at risk of extinction, and that number is expected to rise amid ongoing pollution, overfishing, ocean warming and acidification, according to scientists at the International Union for Conservation of Nature.

Additionally, new threats to ocean organisms and ecosystems could emerge in coming years in the form of deep-sea mining for rare-earth minerals. In Nice, Macron is expected to urge countries to support postponing sea-bed exploration while researchers work to understand deep sea ecosystems.

Scientists are also concerned about the possibility that governments could look to modify ocean chemistry to boost its capacity for absorbing CO2 - a scenario that researchers say could help to limit global warming but could also have unintended consequences.

WHAT ARE THE NEXT STEPS FOR THE TREATY?

Macron's news on Monday of 50 governments having ratified the treaty means it is still short by 10 signatures.

The treaty will enter into force 120 days after 60 countries have ratified it. Work then begins on setting up institutions and committees to implement the treaty, while its signatories expect to hold a first conference within a year.

Despite its involvement in the original treaty negotiations, the United States under current President Donald Trump is not expected to ratify the treaty.

WHAT ELSE IS HAPPENING AT THE U.N. OCEANS CONFERENCE?

Macron is co-hosting this third U.N. Oceans conference with Costa Rica, and with at least 55 heads of state, business leaders and civil society groups expected to attend the five-day event.

Aside from discussions to advance the treaty, delegates are also expected this week to discuss overfishing, water pollution and other threats to marine life.

They'll also be looking for fresh ideas on how to pay for it all - with ocean-linked financing lagging far behind other sustainable investment areas. For the five years spanning 2015-2019, ocean-related spending totalled $10 billion.

By comparison, the U.N. estimates that every year at least $175 billion is needed for marine protection.

The last U.N. oceans summit was held in Lisbon and co-hosted by Kenya in 2022. The next, co-hosted by Chile and Korea, is set for 2028.

(Reporting by Virginia Furness, Editing by Katy Daigle and Hugh Lawson)