I also won’t forget the ship’s captain, Leif Skog, announcing that we had traveled farther north than this expedition ever had before. We knew that was saying something—Skog had been navigating polar waters for four decades. How amazing, we initially thought.

And then, of course, the experience turned sobering as we realized why we’d gotten so far: because sea ice that normally halts the ship’s northward progress had melted. In this issue we look at that and other effects of climate change on the Arctic, from shifting geopolitical power to thawing permafrost.

As soil a couple of feet deep goes from frozen to mush, the release of carbon could push climate change to a tipping point, writer