This story appears in the September 2019 issue of National Geographic magazine.

In the spring of 2018, my husband and I went to the Arctic on a National Geographic expedition. We’d never been before and were struck by the scale of its rugged beauty, the white-blue glaciers glinting in the midnight sun, and the abundant wildlife. I’ll never forget seeing an enormous walrus face down a young polar bear (which wisely decided to move along).

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 Craig Welch reports in “Arctic permafrost is thawing fast. That affects us all.” in this issue. With the Arctic warming much faster than the rest of the planet, Welch writes, “In 2017 tundra in Greenland faced its worst known wildfire.” Meanwhile, “Lakselv, Norway, 240 miles above the Arctic Circle, recorded a blistering 32 degrees Celsius, or 90 degrees Fahrenheit. Arctic reindeer hid in road tunnels for relief.”

Like what I saw in the Arctic, what you’ll read here is thought provoking. May it also be galvanizing, spurring each of us to do what we can to slow the advance of climate change.