The ocean is growing. It’s swelling and rising, encroaching on coasts. This change is creating the first wave of “climate refugees,” writes Elizabeth Rush in her June book Rising, Dispatches from the New American Shore. And in her view, Americans’ best option in the face of rising sea levels may well be to flee the coasts.

“Harvey. Maria. Irma. Sandy. Katrina. We live in a time of unprecedented hurricanes and catastrophic weather events, a time when it is increasingly clear that climate change is neither imagined nor distant—and that rising seas are transforming the coastline of the United States in irrevocable ways,” Rush explains.

Rising sea levels happen naturally because of tectonic movements and melting glaciers. But the current rate of change was hastened dramatically in the 20th century by human-induced global warming. We know this in part due to a clever test devised by scientists who studied Roman fish tanks (pdf) built at the behest of the emperor Augustus, who ruled Imperial Rome from 27 BC to 14 AD. Those fish tanks were built precisely at sea level 2,000 years ago. If sea levels rose consistently over two millennia the way they have in the last 150 or so years, scientists say they’d be under 12 feet of water today. But the fish tanks aren’t submerged, which is just one indication that the recent rising seas are a serious deviation from the slower rate of change in the two millennia since the Romans engineered the tanks.

The seas will only continue to rise. Coastal communities in the US can expect waters anywhere from 2.5 feet to 10 feet higher by 2100. “It is not a question of if but when,” according to Ben Strauss, chief scientist of the nonprofit Climate Central, who has testified before the US Senate about rising seas.

For coastal communities in places like Florida, Louisiana, California, New York, and Maine, that gloomy future is already here. Climate change isn’t an abstraction in Miami or on Long Island, say. It’s a reality experienced in the form of ever-more common storms and perpetual flooding.

Rush spent several years studying the seas, talking to experts, and traveling around the US, meeting the people who are already contending with the problems first-hand. She met working- class families who lost relatives in flooding and were driven from their Long Island homes by Hurricane Sandy in 2012. She met poor Floridians who can’t afford to move out of their trailers or pay mandatory flood insurance. She visited the San Francisco Exploratorium, where an interactive map of sea levels past, present, and future shows that with just two feet of rise, the local airports will be drowned. Rush went to Silicon Valley, where Facebook dumped 72,500 cubic yards of dirt to raise the site of a new corporate campus built on flood-prone former tidal wetlands. The building is perched on 10-foot concrete stilts but the infrastructure the campus relies on, like roads and sewers, remains vulnerable. And she concluded what few wish to admit: Continuing to build along US coastlines may not be sustainable.

“We can move out of the way by choice or else the weather events that we have constructed, are continuing to construct, will make the decision for us,” she writes. “I am not talking about about abandoning our lives on the water’s edge, or the wholesale demolition of seaside property. But I do think the time has come for us to look at the history of our coastal communities and to ask ourselves if rebuilding or continuing to develop in the absolute lowest-lying areas continues to make sense.”

Some communities have already confronted this reality. As Rush explains in her book, the Native Americans of the Isle de Jean Charles in Louisiana off the Gulf of Mexico made a collective decision in 2016 to abandon their ancestral home. “By 2050 there will be 200 million people like them worldwide, two million of whom will be from right here in Louisiana,” Rush writes.

Last November, the Environmental Protection Agency awarded the islanders the 2017 Gulf Guardian Award in the Environmental Justice/Cultural Diversity Category in recognition of the collective decision to leave their disappearing land. “The Isle de Jean Charles Band of Biloxi-Chitimacha-Choctaw is in the process of resettling their community further inland as a result of tremendous land loss. The US Department of Housing and Urban Development awarded a grant that will cover a portion of the cost. Once completed, the resettlement will bring together the now-scattered tribal population while also restoring the ecosystem at the new site,” explains an EPA press release.

It’s an act of self-preservation, as the island’s once-fertile soils and waters are now so salty that trees and plants can’t grow and the marine life people relied on for food is less abundant. Still, it wasn’t a decision that came easily to islanders. Many resisted leaving the place they loved, where generations lived, even as life grew harder and the storms came more frequently, and their houses were raised on stilts.

In Rush’s view, the residents of Isle de Jean Charles made a wise decision, or perhaps just one that seemed inevitable. Retreat may be a sensible proposition, but it’s not a solution most people want to contemplate—even dedicated environmentalists. “The thing is, land in the Bay Area is some of the most valuable per square foot in the country. I don’t see us giving that up anytime soon,” John Bourgeois, the executive project manager of California’s South Bay Salt Pond restoration project protests when Rush suggests less coastal development. She says his is a typical response, but one she fears will only compound problems.

Rush believes that the response to rising sea levels isn’t a steadfast adherence to the coast, more insurance policies, raising the land artificially, or putting buildings on stilts. These are all just intermediate measures, the kind of responses to problems that led us into trouble to begin with. During her visit to California, home of the 19th century gold rush, Rush writes:

I am thinking about how Silicon Valley and the tech industry and the innovative ethos of San Francisco are 21st century versions of the same old get-rich-quick schemes, the same old narrative where the march of progress promises to transmute buried rocks into rocket fuel, deserts in cornfields, thin air into capital, stolen swamplands into private property.

It’s downright unAmerican, perhaps, to propose a solution like retreat, rather than championing the development of new technologies to bolster coasts. But Rush dares to do it because she sees no better way. “What might currently seem like an anomaly—the ‘record-breaking,’ ‘game-changing,’ ‘unprecedented’ 2017 hurricane season—will soon become all too common.”

Like the islanders on Isle de Jean Charles, who came to view their decision to move off the island in a positive light, as a chance to reunite dispersed tribes and revitalize their community, Rush argues that retreat is not defeat. “It is also an opportunity for transformation,” she contends.

It is also accommodating reality. Her book concludes with a list of names of the recent storms that, in just four short months, blew through the lives of the people she met during her years of research. “Franklin. Gert. Harvey. Irma. Jose. Katia. Lee. Maria. Nate. Ophelia,” Rush writes. “I was and still am trying to let the storms in, even knowing they will undo many of the places and relationships we have long cherished.”