French President Emmanuel Macron opened the UN Ocean Conference in Nice on Monday with an urgent call for multilateral action to save the seas.

"The first answer is multilateralism," said Macron. “The deep sea is not for sale, neither is Greenland for sale, nor Antarctica," he added in a veiled response to U.S. President Donald Trump's expansionist statements since he took office in January.

"While the Earth is warming, the ocean is boiling," said the French president, as he called for an "open partnership" in science and research to protect the world's oceans.

"The climate, like biodiversity, is not a matter of opinion; it's a matter of scientifically established facts," he added.

A High Seas Treaty will be ratified by a sufficient number of countries at the summit to enter into force, Macron confirmed, noting that 50 countries had submitted ratifications "in the past few hours" before the UN Ocean Conference officially opened.