With the Olympic Mountains in the background, a small boat crosses in front of an oil rig as it arrives in Port Angeles, Wash., April 17, 2015. (Daniella Beccaria/ASSOCIATED PRESS)

“RENEWED OFFSHORE energy production will reduce the cost of energy, create countless good jobs, and make America more secure and far more energy independent,” President Trump said last week as he signed an executive order meant to expand offshore drilling in federal waters.

In fact, it would take years for the government to merely rewrite its offshore leasing plan. After that, oil prices would have to rebound to the point that energy companies would be interested in exploring and drilling off the Atlantic and Alaskan coasts, which is not a simple business. Opposition from local groups and even the U.S. military would have to be considered. In other words, revised rules on U.S. offshore drilling probably will not upend the much larger global energy equation.

But if Mr. Trump overstated the importance of opening more of the country’s coast to mineral exploitation, his environmentalist critics exaggerated the strength of their case, too. A variety of activist groups sued the Trump administration last week, saying that the president’s new executive order would gravely endanger coastal communities and worsen climate change.

Their intriguing legal argument is stronger than their claims on the policy merits. As long as the world uses oil, it will have to come from somewhere — including repressive petro-states, developing-world offshore deposits, fracked oil wells, Canadian oil sands and other unattractive places. While the United States refuses to drill, it arrogantly benefits from an efficient global oil market in which others take the risks. This situation is probably self-defeating for environmentalists, too: Even under the Trump administration, U.S. oversight will be more stringent than that of many other oil-producing nations. Moreover, if drilling ever did happen along new areas of the U.S. coast, it would provide the country some economic benefits in the form of jobs and revenue.

Environmentalists’ best argument is that the nation cannot fully exploit its oil wealth if it is to take climate change seriously. A lot of fossil fuel will have to remain in the ground. But the only way to keep sufficient quantities of oil in the ground is to cut demand for it, not to haphazardly nix energy projects in a world with many alternative sources of oil. Energy companies will consider future climate efforts as they decide where to drill. If they do this poorly, they will lose money in the long run. Even if the government were to increase its ambition in cutting carbon-dioxide emissions — and it should — it ought to let the private sector determine how to meet the nation’s ongoing need for oil and gas as these fuels are steadily phased out, promoting efficiency and stability in an energy trade that will underpin the economy for some time yet.

The activists, however, have ample reason to criticize another piece of the president’s new executive order: its endangerment of protections for marine sanctuaries, including the Atlantic’s Northeast Canyons and Seamounts Marine National Monument and Hawaii’s Papahanaumokuakea Marine National Monument. These zones have been protected precisely because of their unique ecological value. Some places — if not all places — are simply too pristine for oil drilling.