After years of inaction, the melting of polar ice has added urgency to efforts to have the United States belatedly sign on to the Law of the Sea Convention. Warming seas and air have made long inaccessible deposits of oil, gas and minerals reachable. Without clarity as to who can access these resources, U.S. companies could be left on the sidelines. To avert this and other problems, the treaty should be ratified.

The treaty sets rules for navigation, fishing, seabed mining and other activities in, above and below the world’s oceans. Fifty-five countries, including China and Russia, which continue to assert their maritime authority, have signed on to the treaty, which was first adopted in 1982.

While the U.S. military, shipping industry, energy companies and environmental groups support the treaty, it has languished in the Senate. Although the Senate Foreign Relations Committee has repeatedly supported the measure, it has not come to a vote before the full Senate because of criticism from a small but vocal group of critics concerned that the United States would cede too much control to the United Nations.

It is inaction, however, that could cause the United States to see its control weakened.

Earlier this summer, there was a flurry of activity around the North Pole and Northwest Passage. Canada is talking about increasing its icebreaker fleet and setting up military facilities along the waterway that, with the melting of ice, is close to becoming passable by ships traveling between Europe and Asia.

Russia sent two submarines below the North Pole and planted the country’s flag there. Denmark is studying a mountain ridge under the Arctic Ocean that it may claim is connected to Greenland.

This activity highlights the need for the United States to join the sea treaty, Deputy Secretary of State John Negroponte told senators last month.

“Currently, as a non-party, the United States is not in a position to maximize its sovereign rights in the Arctic or elsewhere,” he said. The treaty creates a formal mechanism for countries to prove their claims to the seabed under the ice cap. The United States is the only country with territory in the Arctic that is not a party to the treaty. The treaty also recognized a country’s rights over the continental shelf out to 200 miles. With its large coastline, the United States has much to protect.

“We have more to gain from legal certainty and public order in the world’s oceans than any other country,” Mr. Negroponte told lawmakers.

In addition to mineral rights, the treaty would ensure that naval vessels could continue to operate unimpeded in international waters. It would also ease the continuation of international efforts to stop the covert ocean shipping of biological, chemical and nuclear weapons.

With so many reasons for the United States to be a party for this treaty and so many diverse groups supporting it, it is past time for the agreement to be ratified by Congress.