Gaia Vince’s “Nomad Century: How Climate Migration Will Reshape Our World” is written for all the right reasons. But it comes to the wrong conclusions. Vince, a British journalist, argues in this compact book that climate change in coming decades will make broad swaths of the globe uninhabitable, and therefore humankind must change its ways.

First, Vince urges that without delay we must decarbonize energy production and shift from fossil fuels to solar, wind, geothermal, tidal and nuclear power, while electrifying transport, heating and every energy-intensive activity.

So far, so unremarkable, even if many would dissent from her enthusiasm for nuclear power.

Her remaining recommendations are, to put it mildly, less routine. An international authority must oversee the orderly migration of hundreds of millions or billions (different parts of the book give different numbers) of climate refugees. With 4 degrees Celsius of warming, “the vast majority of humanity will live in high latitude areas.” That would come to at least 5 billion people.

These refugees must depart warmer latitudes in Asia, Africa and Latin America and resettle in Alaska, Canada, Greenland, northern Europe and Russia as well as Patagonia, Tasmania, New Zealand and Antarctica. Someone must build archipelagoes of new cities in the far north and far south of the planet to house them. Meanwhile, to stabilize the climate, we need to abandon squeamishness and embrace several forms of geoengineering. Finally, to do that properly, we must empower a “global governance body” to set the planet’s thermostat.

What could go wrong?

“Nomad Century” is a curious mix of apocalyptic planetary pessimism and unbounded optimism about the better angels of human nature. Vince examines scenarios for the unfolding climate crisis and chooses those nearer to the alarmist end of the spectrum, although remaining, in my view, within the bounds of the plausible. There is one notable exception – where she writes of warming “by a few degrees (Celsius) each decade,” which is far outside the range of scientific projections.

She foresees massive tragedies in the tropics and subtropics due to baking heat, water shortages and crop failures. She could be right – the climate crisis is likely to be the overriding problem of the 21st century. She thinks that Asians, Africans and Latin Americans will not be able to adjust to the magnitude of these challenges. Perhaps she is right there, too.

Vince’s prescription of assisted mass migration, however, is a recipe for political disaster. She imagines that a “UN Migration Organization with real powers to compel governments to accept refugees” could persuade or force Russians, Scandinavians, British, Greenlanders, Canadians, Alaskans and New Zealanders to welcome hundreds of millions (or billions) of poor strangers into their midst and to help provide them with jobs, health care and language lessons.

But any such gigantic flows of refugees, especially if their resettlement were overseen by an international body with “powers to compel,” would trigger torrents of outrage. Vince’s vision requires that every high-latitude country accept refugees in numbers that would swamp the native-born. A new generation of Orbans and Bannons – and worse – would eagerly encourage and exploit anti-migrant fears. Pogroms would proliferate.

She points to the history of the Nansen passport, devised in the 1920s to help stateless refugees, as support for the feasibility of her plan. But only about 450,000 Nansen passports were furnished in the 16 years they existed. Had hundreds of millions been issued, no country would have honored them.

Vince recognizes some of the difficulties, noting that for her plan to succeed, humans would first have to abandon racism, chauvinism and nationalism and become citizens of the world. Like John Lennon and Yoko Ono, she cannot be faulted for lack of imagination.

Her prescription also implausibly presumes it is feasible to build hundreds of new cities in the higher latitudes. Boreal landscapes have thin soils, scraped bare in the last glaciation, that even in a warmer world could scarcely support crops. She recommends paying for the flurry of city-building and refugee settlement with “an international tax” or “public-private partnerships.”

Vince’s optimism extends to geoengineering. She regards it as “morally indefensible” not to use whatever tools we have that might cool the planet. Her tool kit includes the standard ideas: She recommends fertilizing the oceans with iron to stimulate plankton growth and thereby remove carbon from the atmosphere. She urges the creation of an international authority to oversee the injection of sulfate aerosols into the stratosphere to reflect sunshine back into space. She regrets the “taboo” against geoengineering, choosing a word that makes caution seem like an irrational fixation of a benighted tribe. She is blithe about the risks of experimenting with large-scale Earth systems, saying that if geoengineering interventions produced unhappy side effects, we could just stop. This takes no account of nonlinear responses, or tipping points, that can shift complex systems such as climate into a new condition from which it is exceedingly hard to return.

Vince’s take on geoengineering involves political optimism too. Any “global governance body” able to set the planet’s thermostat would quickly run into irreconcilable differences. It’s hard enough for a family to agree on the proper thermostat setting for a home. She is aware of this problem, but her only answer is that the body should be appointed immediately to start work.

Vince has read widely but often leaves her sources unmentioned. Readers who want to know where she got the notion that ancient Greeks were descended from steppe nomad warriors, or that 40 percent of East Africa’s rainfall comes from groundwater exploitation in India, are left in the dark. This makes it harder than it should be to assess the quality of the science on which she relies.

Vince’s wrongheaded recommendations come from having her heart in the right place. She is deeply, and appropriately, concerned about the likely plight of billions of the world’s least fortunate as our climate continues to warm. And she is right to emphasize the perils that climate change portends. But “Nomad Century” recommends cures that could easily prove worse than the disease. Her proposals for internationally overseen mass migrations and grand-scale geoengineering require faith in widespread saintliness and wisdom that humankind has yet to show.

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J.R. McNeill is a professor of environmental history at Georgetown University.