As sea levels rise by multiple feet in the coming decades, communities along the coastal United States will face increasingly frequent flooding from high tides and tropical storms. Thousands of homes will become uninhabitable or disappear underwater altogether. 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 won’t happen in a uniform manner, because migration never does. In large part this is because young adults move around much more than elderly people, since the former have better job prospects. It’s likely that this time-tested trend will 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 has jumped since 2017’s Hurricane Maria, as young people leave the U.S. territory for the mainland states.

A new paper published in the prestigious Proceedings of the National Academy of Sciences offers a glimpse at the shape and scale of this demographic shift as climate change accelerates. Using sea-level rise models and migration data gleaned from the latest U.S. Census, the paper projects that outmigration from coastal areas could increase the median age in those places by as much as 10 years over the course of this century. That’s almost as much as the difference between the median age in the United States and the median age in Japan, which is among the world’s most elderly countries.

Climate-driven migration promises a generational realignment of U.S. states, as coastal parts of Florida and Georgia grow older and receiving states such as Texas and Tennessee see an influx of young people. It could also create a vicious cycle of decline in coastal communities, as investors and laborers relocate from vulnerable coasts to inland areas — and in doing so incentivize more and more working-age adults to follow in their footsteps.

“When we’re thinking 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 of the paper.

Read the full article about climate migration by Jake Bittle at Grist.