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It鈥檚 an obvious truth that rising seas are going to displace a lot of people. How many, and how fast, depends on many factors, especially the stability of marine-based glaciers in west Antarctica.

Recent studies indicate that , and that in more extreme scenarios who live at lower elevations would be put in jeopardy. Where exactly will these people go? What impact will they have on the cities and states they flee to?

Mathew Hauer, a geographer at the University of Georgia in Athens, has taken a stab at answering these questions in a paper published this week. Focusing on the US, he has looked at studies identifying populations at risk if sea level rises 1.8 metres by 2100, and has scrutinised 319 counties where more than 13 million people are likely to be displaced.

Hauer reasons that they are likely to follow paths of earlier migrants and refugees, those paths often defined by location of family, friends and economic opportunity.

To try to predict the patterns, he has used Internal Revenue Service figures that show county-to-county migration from 1990 to 2013. The most compelling and thought-provoking result is that rising seas are not just a problem for coastal elites with their beach houses and waterfront condos. Every state in the US will be impacted, either by residents fleeing or by people seeking refuge.

鈥淚t鈥檚 not hard to imagine a flood-driven version of The Grapes of Wrath鈥�

Nine states will see population declines. Florida is the biggest loser by far, with more than 2.5 million residents heading for higher ground. Texas is the biggest gainer, with 1.5 million new residents, and is the largest recipient of those leaving Florida.

Among cities, the biggest losers are Miami (2.5 million fewer people), New Orleans (500,000) and New York (50,000). The biggest gainers are Austin, Orlando and Atlanta, each with 250,000 or more new residents by 2100.

In a perfect world, this population surge could be seen as a boon for these destinations. But as Hauer points out, many of the cities that would swell 鈥� Phoenix, Las Vegas, Atlanta 鈥� already have water and growth-management issues.

Depending on how fast seas rise, migration could happen in an orderly fashion, giving officials time to adapt. But it may not. It鈥檚 not hard to imagine a flood-driven version of The Grapes of Wrath, John Steinbeck鈥檚 great American novel about people fleeing the dust bowl and living in roadside camps in California.

Migration and conflict

Hauer doesn鈥檛 extend his study beyond the US, but the implications are even darker for countries such as Bangladesh, Indonesia and Nigeria, where tens of millions of people are at risk.

For low-lying nations like these, sea level rise threatens chaos, poisoning farmlands, polluting drinking water supplies and driving people from their homeland.

The link between forced migration and political conflict is self-evident today, with borders tightening and fear of outsiders rising. Even the US Department of Defense openly acknowledges the role climate change plays in generating conflict, calling it .

Hauer鈥檚 study is just a first pass at coming to grips with all this. It suggests that even the wealthy US is woefully unprepared for what is to come. Hauer points out that although spending money on adaptation, such as building levees, can reduce the number of people who flee coastal cities, it won鈥檛 help that much.

Equally important, political leaders should encourage an orderly retreat from obviously doomed areas by amending laws that dictate what can be built and where, instigating buyouts of high-risk homes, setting flood insurance rates that accurately reflect risks, and offering other economic incentives.

But the larger truth is that as rising seas eat away at the world鈥檚 coastlines, it鈥檚 going to impact everyone. You can build all the walls you want, but as Hauer鈥檚 work demonstrates, in the end, we are all in this together.