The mass migrations have begun.

A woman in Charleston moves out of a house that has flooded three times in three years.

Millions of Americans will confront similarly hard choices as climate change conjures up brutal storms, flooding rains, receding coastlines and punishing heat. Many are already opting to shift to less perilous areas of the same city, or to havens in other states. Whole towns from Alaska to Louisiana are looking to relocate, in their entirety, to safer ground.

The era of climate migration is, virtually unheralded, already upon America.

The population shift gathering pace is so sprawling that it may rival anything in US history. “Including all climate impacts it isn’t too far-fetched to imagine something twice as large as the Dustbowl,” said Jesse Keenan, a climate adaptation expert at Harvard University, referencing the 1930s upheaval in which 2.5 million people moved from the dusty, drought-ridden plains to California.

This enormous migration will probably take place over a longer period than the Dustbowl but its implications are both profound and opaque. It will plunge the US into an utterly alien reality. “It is very difficult to model human behaviour under such extreme and historically unprecedented circumstances,” Keenan admits.

The closest analogue could be the Great Migration – a period spanning a large chunk of the 20th century when about 6 million black people departed the Jim Crow south for cities in the north, midwest and west.

…

“The Great Migration was out of the south into the industrialized north, whereas this is from every coastal place in the US to every other place in the US,” said Hauer. “Not everyone can afford to move, so we could end up with trapped populations that would be in a downward spiral. I have a hard time imagining what that future would be like.”

Grim.

Within just a few decades, hundreds of thousands of homes on US coasts will be chronically flooded. By the end of the century, 6ft of sea level rise would redraw the coastline with familiar parts – such as southern Florida, chunks of North Carolina and Virginia, much of Boston, all but a sliver of New Orleans – missing. Warming temperatures will fuel monstrous hurricanes – like the devastating triumvirate of Irma, Maria and Harvey in 2017, followed by Florence this year – that will scatter survivors in jarring, uncertain ways.

I’m not sure about the “few decades” part, since that’s just more of what’s already happening.