Last week, nine countries—the U.S., Canada, Russia, Norway, Greenland/Denmark, China, Japan, Iceland, South Korea, and the European Union (which includes 28 member states)—signed a treaty to hold off on commercial fishing in the high seas of the Arctic Ocean for at least 16 years while scientists study the potential impacts on wildlife in the far north. It was an extraordinary act of conservation—the rare case where major governments around the world proceeded with caution before racing into a new frontier to haul up sea life with boats and nets. They set aside 1.1 million square miles of ocean, an area larger than the Mediterranean Sea.

But to really grasp the significance of this milestone, consider why such a step was even possible, and what that says about our world today. For more than 100,000 years the central Arctic Ocean has been so thoroughly covered in ice that the very idea of fishing would have seemed ludicrous.

That remained true as recently as 20 years ago. But as human fossil-fuel emissions warmed the globe, the top of the world has melted faster than almost everywhere else. Now, in some years, up to 40 percent of the central Arctic Ocean—the area outside each surrounding nation’s 200-nautical-mile exclusive economic zone—is open water in summer. That hasn’t yet been enough to make fishing attractive. But it is enough that boats may be lured in soon.

So, for perhaps the first time in human history, the nations of the world set aside and protected fishing habitat that, for the moment, does not even yet exist. The foresight is certainly something to applaud. But it’s hard to escape the fact that the international accord is a tacit acknowledgment—including by the United States, which is moving to back out of the Paris climate accords—that we are headed, quite literally, into uncharted waters.

“The Arctic is in a transient state—it’s not stable,” Rafe Pomerance, a former State Department official who once worked on Arctic issues and now chairs a network of Arctic scientists from nongovernmental organizations and serves on the polar research board of the National Academy of Sciences, said last year.