We share a fascination with the ocean that has led us since childhood to wander the world under the waves. We also share an increasing concern that the health of the ocean is rapidly deteriorating under the strain of human pressure and neglect. The evidence is everywhere, from plastic waste at the bottom of the Arctic Ocean to flattened remains of deep ocean reefs hundreds of miles from land, bulldozed by bottom trawlers. No part of the ocean is safe anymore.

At particular risk are waters that lie beyond the jurisdiction of any country, the high seas. This vast realm constitutes two-thirds of the oceans, covers nearly half the planet's surface and harbors the largest reservoir of unexplored biodiversity left on Earth. Yet these waters face escalating pressure from overfishing, deep seabed mining, acidification, chemical and noise pollution, plastic waste, dead zones, ship traffic and destructive fishing tactics.

Like most commons, the high seas are poorly regulated. Environmental controls on mining, fishing, pollution and shipping are inconsistent, weak or altogether absent. There are no uniform requirements to assess industrial activities and no mechanisms to create marine refuges where sea life can live undisturbed.

In the controlled waters of the United States and other nations, governments have set aside reserves for ocean life. In contrast, less than one-three-hundredth of 1 percent of the high seas has been protected. Scientists believe that such protected areas are essential for ocean health.

An important opportunity to begin responsibly managing half the planet lies before us. The United Nations is holding meetings to discuss the future of the high seas. A coalition of nations has proposed an international agreement to modernize governance of the high seas.

The agreement would provide for protected areas and would require countries proposing to engage in destructive activities to assess and manage their effects. It would also deal with the lack of any rules governing how revenue derived from genetic resources in international waters will be shared, an important bar to commercializing new products. Most important, it would begin to bring to the high seas modern management as practiced in the U.S. and elsewhere since the 1970s.

The United States has been the single most significant obstacle to a new high seas agreement, with the State Department citing potential opposition from members of Congress who are critics of the United Nations. Possible opposition from pharmaceutical, biotech and cosmetics companies involved in marine genetic research has also been mentioned, although no such opposition has surfaced.

We do not believe it makes sense to hold this hugely important initiative hostage to possible opposition or unspecified potential concerns. This is not leadership.

Spearheading negotiations on the conservation and management of the high seas could give the U.S. a big win on a global issue. It would level the playing field by making sure that activities on the high seas are subject to the same kinds of requirements routinely imposed on ocean industries in U.S. coastal waters. Such an agreement would also provide predictability and certainty to companies that take risks to develop commercial products from areas beyond national jurisdiction.

How many chances does a president get to influence the future of half the planet for the benefit of all that live on it? That opportunity is here. We urge President Barack Obama and Secretary of State John F. Kerry to seize it by joining the call for a new agreement to protect the high seas.

Richard Branson is founder and chairman of Virgin Group. James Cameron is a film director and deep-sea explorer. They wrote this for the Los Angeles Times.

Distributed by MCT Information Services