There has been a lot of talk about the millions of people worldwide whose homes will be at the mercy of rising sea levels. Within the US, a 1.8-meter rise in the oceans by 2100 could displace as many as 13.1 million people. Worldwide, up to 180 million people could be at risk.

There has been less talk about where exactly those people will go when they leave their homes. Research on climate migration has painted sea level rise as “primarily a coastal issue,” writes Mathew E. Hauer in Nature Climate Change this week. But the inland regions that absorb climate change migrants will need to have sufficient transport, housing, and infrastructure to absorb the migrants.

To get a picture of what this might look like within the US, Hauer combined two different sets of data in a predictive model. This kind of model relies on a lot of different assumptions, but it provides a starting sketch of what the impact on inland areas might be.

Who goes where

The IRS collects data on migration by recording when someone’s tax return is filed in a different location from one year to the next. So the IRS data shows patterns in migration within the US. Migration decisions aren’t random: people pick new locations based on networks of family and friends, employment opportunities, and other factors like booming economies or good infrastructure.

Hauer combined the IRS data with the climate migration models that suggest 13.1 million US Americans will be displaced during this century.

Texas will probably be the state absorbing the greatest number of climate migrants, according to the model, possibly as many as 1.5 million. Georgia and North Carolina are next in line. Florida could lose as many as 2.5 million people, and Louisiana and New Jersey are also likely to be particularly hard hit by migration away from coastal zones. But “no state is left untouched,” Hauer writes. And there will also be migration within states, meaning that more than half the counties in the US are likely to be affected by migration.

But the precise numbers are not the most important thing about the research, writes environmental researcher Jeroen C. J. H. Aerts in a commentary in Nature; the really essential thing is just flagging the topic as one desperately in need of more research.

Limited models

Aerts points out some of the assumptions in Hauer’s model that might not hold up under scrutiny. For a start, people might not follow IRS immigration patterns when they migrate for climate-related reasons. There’s also the likelihood that at least some of these areas threatened with being swamped will choose to invest in protective infrastructure, so far fewer people end up needing to leave. “Such measures are likely to be implemented because of the high cost of not investing in protecting urban land and infrastructure,” Aerts writes.

That's not to say Hauer didn't recognize some of the complexities of migration. Some people might not choose to move very far, he notes, simply relocating within the same general region or to other, safer coastal regions.

There’s also the question of who can afford to get out. Hauer assumes that people earning above a certain level might choose to stay and pay for protective infrastructure, while Aerts points out that it’s likely to be the poorest people who are trapped in a region with no opportunity to leave. And the model doesn’t account for migration into the US from other countries affected by sea rise or migration from regions suffering from other climate-related problems like drought.

“There is much we still do not know about how climate change will influence migration,” Aerts writes. “[Hauer] has (perhaps indirectly) made the case that rigorous adaptation in coastal areas is urgently needed, especially in developing countries where millions of people do not have the option of leaving these areas.”

This is really just the start of a much bigger conversation, and hopefully more models will be built to see how different assumptions play out. Understanding more about these patterns is vital work—and that conversation needs to extend to inland areas and the infrastructure they need.

Nature Climate Change, 2016. DOI: 10.1038/nclimate3271 (About DOIs).