“It’s cold on the Wall.” So begins John Lanchester’s taut tale of a future Britain after the Change, a devastating climate event. This Wall is no steel-slat barrier or see-through fence; it’s a concrete monster entombing the entire island, 6,000 miles long, 16 feet high, and 10 feet thick. It holds back the rising seas and keeps out climate refugees, referred to as the Others. The Wall is patrolled by young conscripts known as Defenders, including Kavanagh, the protagonist.

The novel, just published in Britain and scheduled for U.S. release in March, represents a disturbingly plausible hypothesis about how societies might react to the devastation of climate change. In the text, Lanchester is vague about the precise nature of the Change, but in a recent episode of the “Talking Politics” podcast, he said that he posited a four-degree Celsius temperature increase that produces rising seas and disrupts the Gulf Stream, accounting for the island’s frigid climate. David Wallace-Wells, author of the new book “The Uninhabitable Earth,” sees Lanchester’s four-degree scenario as firmly within the realm of possible outcomes by the end of this century.

The novel begins as Kavanagh starts his compulsory two-year tour as a Defender. The work is cold and lonely. Defenders stand guard atop the Wall (officially: The National Defense Structure), armed with rifles and scanning the sea for incoming Others. For much of the time, nothing happens. But intermittently and terrifyingly, Others try to fight their way over the Wall in groups ranging from two to two dozen. The fates of Others and Defenders are tied together: For every Other that makes it over the Wall, a Defender is put to sea, an effective death sentence.

We learn about the politics of this fortress state from Kavanagh’s point of view. He occasionally sees the contrails of a plane overhead, using up the scarce remaining aviation fuel to fly a member of the elite to useless summits about how to fix the broken world. There is nothing much to be done; it’s too late.

The political class in “The Wall” take pride in their resoluteness amid a disintegrating world — a common English conceit that holds come hell or high water. Politicians give speeches about the heroism of the Defenders, the heroism of Britain and how through continued heroism Britain will prevail as it has always prevailed. Listening to one of these speeches, Kavanagh enters a reverie in which he imagines politicians “born from chrysalises, already wearing their shiny suits, their ties pre-knotted, their first clichés already on their lips, being wiped down of cocoon matter and pushed towards a podium.”

Kavanagh doesn’t have the time or the energy for political machinations. He does, though, feel the intergenerational hostility that shapes post-Change Britain. He cannot stand to talk to his parents, and they are so ashamed by what they have wrought that they cannot talk to their son. As Kavanagh puts it, “you know that thing where you break up with someone and say, It’s not you, it’s me? This is the opposite. It’s not us, it’s them. … [T]he olds feel they irretrievably f---ed up the world, then allowed us to be born into it. You know what? It’s true. That’s exactly what they did.”

In their important recent book “Climate Leviathan: A Political Theory of our Planetary Future,” Geoff Mann and Joel Wainwright sketch four possible paths for politics in a climate-changed world. In the first, which they term Climate Leviathan, capitalist elites coordinate a transnational response via a global technocratic authoritarianism. In Climate Behemoth, these efforts are defeated by reactionary nationalisms, leaving isolated garrison states fighting for survival on their own terms. In Climate Mao, noncapitalist powers unleash a “just terror” to force reductions in global climate emissions. In Climate X, a revolution for climate justice brings about a post-capitalist, post-national world.

“The Wall” shows Britain as a reactionary Climate Behemoth, with the rest of the world in a state of social and political collapse. The British elite of Lanchester’s story have made the political and economic modifications necessary to retain their own privileged positions and beggared the rest of the species. The Wall keeps out the Others. The Defenders are conscripted to guard the Wall. Those few Others who make it over the Wall are either shot or enslaved; known as the Help, they become domestic labor for British citizens, servants to a prison state that they risked their lives to break into.

Lanchester is a long-standing student of climate science, and he told “Talking Politics” that he remains mystified by the lack of a political response to the clear and present dangers it exposes. His biggest puzzlement is why climate has become an issue associated with parties of the left or, alternately, why is it that “conservative parties don’t actually seek to conserve?” He notes that very few world leaders have a background in science, and one who did, Margaret Thatcher, sounded the alarm on climate relatively early on. He wonders about a counterfactual world in which Thatcher had managed to successfully reorient conservative politics toward climate action.

It’s not clear what it will take to finally convince us that it’s time to panic about climate change, but works of fiction such as “The Wall” have an important role to play. Fiction reflects and shapes what society is thinking, including the precise form its nightmares take in any particular era. For those coming of age in the mid-to-late 20th century, the recurrent nightmare was nuclear holocaust. For generations from here on out, climate change will haunt sleep, both for what it will do to our planet and for what it will do to our societies.

Stephen Benedict Dyson (@sbdyson) is an associate professor of political science at the University of Connecticut and a contributor to The Monkey Cage. His book, “Imagining Politics: Interpretations in Political Science and Political Television,” is forthcoming with University of Michigan Press.