ALBEDO IS A CURIOUS WORD, long unfamiliar to even the most informed. But it is soon to become much better known — and not least because it figures importantly in Sara Wheeler’s latest book.

Unaltered from its Latin root, the word means “whiteness.” It describes a property possessed by snow and powdered titanium dioxide, for example, but entirely absent from coal. Some few cooks know it as the white pith beneath the zest of a lemon. But the meaning about to burst onto the world’s linguistic stage is one climatologists and astrophysicists have employed for a long while: it is the whiteness of the reflection of sunlight from our planet’s two giant and ever-glaring polar ice caps.

Sara Wheeler, whose literary wanderings around the world’s highest latitudes over the past two decades have won her a faithful and respectful following, makes it clear that the albedo is presently very much in trouble. Because for centuries past there has been near limitless ice around both poles, the planet’s albedo has long been in good shape, the sun’s scorching brilliance hurled back from whence it came, as if by a mirror. Now, however, the polar ice is melting, it is becoming gray and thin and piebald, in places nonexistent — with the result that the sun’s rays are now flooding inward, unreflected, and are being absorbed into the earth, heating it to ever-higher ambient temperatures. In other words, the poles that were once so critical to helping our world stay cool are fast becoming crucial mechanisms behind our planet’s much-anticipated and widely feared climatic tipping point.

Wheeler, who is known for writing about lonely places and heroic travelers, has long been intrigued by the awful majesty of the world’s two poles; Terra Incognita, which she wrote about the Antarctic ten years ago, has become deservedly something of a classic. Now, with The Magnetic North: Notes from the Arctic Circle, she has decided to examine the very different world of the Arctic. This is both apposite and commendable, since the climate crisis that enfolds the planet is likely to wreak permanent changes on the lives of those who live in the region.

And that, of course, is the principal difference between the world’s two polar extremes. The Antarctic is all land, unclaimed, unpopulated, and has the whole world trying hard to maintain its pristine condition. The Arctic, however, is sea edged by polar lands with national identities. Arctic dwellers present a mélange of humanity made up of those who pay fealty to nations; of those who, like the Eskimos, the Inupiat, and the Sami, belong to a pan-Inuit polar culture and who are rather less inclined to pay fealty to anyone; and lastly, of a scattering of freebooting resident adventurers for whom the Arctic is, as it were, cool.

In traveling from northern Baffin Island to Greenland, from Barrow to the Chukchi Sea, Wheeler has produced a melancholy tone poem of great and lyrical beauty, an account that rivals all of the greatest Arctic writers who have gone before her. And she is evidently tough and resourceful: when she writes of the Sami, she does not merely admire their ability to breast-feed their babies while simultaneously herding their reindeer, but adds casually, “I tried this when I was among the herders in 2002 and found it an impossible, Houdini-like maneuver.” (The child, Reg, flourishes today, with no memory of his once-attempted Arctic breakfast.)

This is also an unflinching book of reportage: it looks at loneliness and pollution, alcoholism and illness, and all the other problems that greed, thoughtlessness, national self-interest, and colonialism have visited on a territory that could once have been so special, so lovely, so protected.

Of all her wanderings, what I found most haunting was when she ventured from Murmansk on a Russian icebreaker, bound across the Arctic Sea. This was especially moving because she brought her older son, Wilf, to show him what was happening to her beloved North. She writes: “It was his future that was at stake in the Big Melt.” And this is where Sara Wheeler explains, and very patiently for those of us outside her world who may not know, just why it is at stake — because the ice that is melting fast now may soon melt a great deal faster, and the world may in consequence suddenly tip into a new era of warming that is quite unlike the timid simmering we are experiencing today.

It all has to do with the graying of the ice cap and the resulting weakening of the albedo, an unfamiliar concept signified by a hitherto unfamiliar word. Thanks to this bravely wandering author — and perhaps those in young Wilf’s generation, as they start to spread the word — is about to become very well known indeed.