President Obama’s decision to forbid oil and gas drilling in nearly all United States waters in the Arctic is in itself a spectacular environmental gift, offering protection to what he accurately described as a “sensitive and unique ecosystem that is unlike any other region on earth.”

It also adds one more chapter, though probably not the last, to the administration’s eight-year record of rebalancing the scale between the conservation of natural resources and their exploitation. And it sharpens an already glaring contrast between Mr. Obama and his successor, Donald Trump, who on the basis of his cabinet appointments alone seems hellbent on reviving the “drill, baby, drill” sensibilities of the George W. Bush administration.

The White House announcement was coordinated with similar steps announced by Prime Minister Justin Trudeau of Canada. Neither announcement affects state-owned waters along the coasts, but together they will shield nearly all of the Beaufort and Chukchi Seas north of Alaska from drilling.

Mr. Obama based his decision on a provision in the Outer Continental Shelf Lands Act, which governs oil and gas activities in federal waters. The provision gives a president unilateral authority to “withdraw from disposition” any unleased lands on the shelf. Despite Senator Ted Cruz’s complaint that this was simply one more “Obama abuse of power,” the provision, though rarely used, goes back as far as President Dwight D. Eisenhower, who used it to protect the reefs off Key Largo, and has since been invoked by Democratic and Republican presidents alike. Mr. Obama previously used it to bar drilling in the rich fishing grounds of Alaska’s Bristol Bay and parts of the Bering Sea.