As sea levels rise by multiple feet in the coming decades, communities along the coast of the United States will experience increasingly frequent inundation from high tides and tropical storms. Thousands of houses will become uninhabitable or completely disappear under the water. For many in these communities, these risks are poised to drive migration away from places like New Orleans, Louisiana, and Miami, Florida — and toward inland areas that face less danger from flooding.
This migration will not happen in a uniform way because migration never happens. This is largely because young adults move around much more than the elderly, as the former have better job prospects. This time-tested trend is likely to hold true as Americans migrate away from climate disasters: The phenomenon has already been observed in places like New Orleans, where elderly residents were less likely to evacuate during Hurricane Katrina in 2005, and in Puerto Rico, where the median age jumped since 2017’s Hurricane Maria, as young people leave the US territory for the continental states.
A new paper published in the prestigious Proceedings of the National Academy of Sciences provides a glimpse into the shape and extent of this demographic shift as climate change accelerates. Using sea-level rise models and migration data obtained from the latest US census, the paper predicts that out-migration from coastal areas could increase the median age in those places by as much as 10 years over the course of this century. This is almost as much as the difference between the median age in the United States and the median age in Japan, which is one of the world’s most elderly countries.
Climate-driven migration promises a generational realignment of US states, as coastal parts of Florida and Georgia age and receiving states like Texas and Tennessee see an influx of young people. It can also create a vicious cycle of decline in coastal communities, as investors and laborers move from vulnerable coastal areas to inland areas – thereby encouraging more and more working-age adults to follow in their footsteps.
“When we think about the effect of climate migration on population change, we have to think beyond just the migrants themselves and start thinking about the second-order effects,” said Mathew Hauer, a professor of geography at Florida State University and the lead author. author of the paper.
In his previous research, Hauer produced some of the only nationwide climate migration projections for the United States. His previous papers modeled a slow shift away from coastlines and toward inland southern cities like Atlanta, Georgia and Dallas, Texas. Millions of people could eventually join this migration movement by 2100. The new article seeks to add a new dimension to that demographic analysis.
“It’s a very large amount of aging in these extremely vulnerable areas,” Hauer said. “The people who are left behind are much older than we would expect them to be, and conversely, the areas that get a lot of people are getting younger.”
The effects of this kind of demographic shift pose thorny problems for aging communities. A lower share of working-age adults in a given city means fewer people giving birth, who can juice future growth. It also means fewer construction workers, fewer doctors, fewer waiters, and a weaker workforce overall. Property values and tax revenues often fall as growth stalls, leading to an erosion of public services. All these factors, in turn, push more people to leave the coast – even those who are not themselves affected by flooding due to sea level rise.
“If Miami starts losing people, and there are fewer people in Miami, then there’s a lower demand for every occupation, and the likelihood of someone moving to Miami instead of moving to another place also decreases, Hauer said. “Maybe like a retiree from Syracuse, New York … who previously might have thought about retiring in Miami, now they decide they’re going to retire in Asheville.”
This vicious cycle, which Hauer and his co-authors call “demographic amplification,” can drive climate migration patterns. The authors predict that about 1.5 million people will move away from coastal areas under a future scenario with about 2 degrees Celsius of warming by 2100, but when they take into account the domino effect of the age transition, the estimate jumps to 15 million. Hauer said that even he was surprised by the extent of the change.
The state most affected will be Florida, which has long been one of the nation’s top retirement destinations, as well as the coastlines of Georgia and South Carolina. Millions of people in these areas face significant risk of sea level rise over the rest of the century, and even parts of fast-growing Florida will begin to shrink as the population ages. Charleston County, South Carolina, alone could lose as many as 250,000 people by 2100, according to Hauer and his co-authors.
The biggest winners under this age-based model, meanwhile, are inland cities like Nashville and Orlando, which are not too far from vulnerable coastal regions but face much less danger from flooding. The county that includes Austin, Texas, could add more than half a million people, equivalent to a population increase of nearly 50 percent. Many of these places have already flourished in recent years. Austin, for example, has seen an influx of young newcomers from California during the COVID-19 pandemic.
The new study offers welcome insight into the demographic consequences of climate migration, according to Jola Ajibade, an associate professor of environmental science at Emory University who was not involved in the new research. But she cautioned that there are other factors that can determine who leaves a coastal area, particularly how much money that area spends to adapt to sea-level rise and flooding.
“I give [the researchers] kudos to you for even leading us in this direction, because we have tried to bring demographic differentiation in the question of who can move, and where,” Ajibade said. “But exposure is not the only thing you need to model, you also need to model vulnerability and adaptive capacity, and those things are not necessarily modeled. It could change the outcome.”
The authors note that they cannot account for these adaptation investments, nor can they track migrants who may move within one country rather than from one country to another. Even so, Hauer says, the paper provides a clear signal that the future scale of climate migration is far greater than just the people driven from their homes by flooding. Both coastal and inland areas, he said, must be prepared for far greater demographic changes than they might expect.