Michael Byers teaches global politics and international law at the University of British Columbia. My first encounter with the Sirius Patrol came after I’d delivered a speech at a conference in Nuuk, Greenland, in 2019. A young man wearing Danish military camouflage approached me. He was tall and lean, with a weather-beaten face and piercing blue eyes. “You’re right about the Arctic being a dangerous place,” he said. “Last winter, I travelled by dog sled along the coast of northeastern Greenland.” “Did you see anyone?” I asked. “No people,” he smiled. “No Russians, no Chinese, but lots of hungry polar...