WHEN THE INTERNET goes down, life as the modern American knows it grinds to a halt. Gone are the cute kitten photos and the Facebook status updates—but also gone are the signals telling stoplights to change from green to red, and doctors’ access to online patient records.

A vast web of physical infrastructure undergirds the internet connections that touch nearly every aspect of modern life. Delicate fiber optic cables, massive data transfer stations, and power stations create a patchwork of literal nuts and bolts that facilitates the flow of zeros and ones.

Now, research shows that a whole lot of that infrastructure sits squarely in the path of rising seas.

Scientists mapped out the threads and knots of internet infrastructure in the U.S. and layered that on top of maps showing future sea level rise. What they found was ominous: Within 15 years, thousands of miles of fiber optic cable—and hundreds of pieces of other key infrastructure—are likely to be swamped by the encroaching ocean. And while some of that infrastructure may be water resistant, little of it was designed to live fully underwater.

“So much of the infrastructure that’s been deployed is right next to the coast, so it doesn’t take much more than a few inches or a foot of sea level rise for it to be underwater,” says study coauthor Paul Barford, a computer scientist at the University of Wisconsin, Madison. “It was all was deployed 20ish years ago, when no one was thinking about the fact that sea levels might come up.”

“This will be a big problem,” says Rae Zimmerman, an expert on urban adaptation to climate change at NYU. Large parts of internet infrastructure soon “will be underwater, unless they’re moved back pretty quickly.”

Tangled Web

The physical structure of the internet has been laid somewhat haphazardly over the past few decades as demand for connectivity has boomed, with lines often laid opportunistically alongside power lines, roads, or other big infrastructure. But the telecommunication companies that own those lines, power supplies, data transfer stations, and other components keep their exact location information private.

Barford, one of the study authors, spent the last few years carefully scraping the web for whatever scraps of publically available information he could find about the locations of those components and mapping his results. Many of those important pieces, he and his graduate student Ramakrishnan Durairajan found, were really close to the coasts.

When Carol Barford, a climate scientist at the University of Wisconsin at Madison, saw the maps, she saw something else: risk. She knew that sea levels have been rising steadily for the past hundred years as Earth’s climate has warmed, and that’s already affecting many coastal areas.

When the three researchers laid the map of the internet’s physical infrastructure on top of sea-level rise prediction maps, they saw a striking overlap: Huge sections of important infrastructure were in the places likely to be underwater within 15 years.

Cities like New York, Miami, and Seattle are likely to see up to 12 inches of extra water by 2030—well inside the time range of a mortgage on a house, or the planning horizon for big public infrastructure projects. A foot of extra water wending through some of those cities, the researchers say, would put about 20 percent of the nation’s key internet infrastructure underwater.

“The 15-year predictions are really kind of locked in,” Carol Barford says. There’s so much inertia in the climate system that there’s nothing humans can to do stop the seas from rising within that time frame.

It’s All Connected

Scientists, planners, and businesses have long known that sea-level rise threatens physical infrastructure like roads, subways, sewage discharge networks, and power lines. But until now, no one had looked specifically at how higher water will affect the physical manifestation of the internet.

“Considering how interconnected everything is these days, protecting the internet is crucial,” says Mikhail Chester, the director of the Resilient Infrastructure Laboratory at the University of Arizona. Even minor hits, like when storms knock out internet connectivity for a few days, can affect things we take for granted, from traffic lights to flight patterns.

This new study “reinforces this idea that we need to be really cognizant of all these systems, because they’re going to take a long time to upgrade,” he says.

The researchers didn’t look at how short-term high-water events like storm surges from hurricanes would affect the infrastructure, but they warned planners to keep the short-term threats in mind when they look at solutions.

“We live in a world designed for an environment that no longer exists,” says Rich Sorkin, the co-founder of Jupiter Intelligence, a company that models climate-induced risk. Accepting the reality of what future will look like, he says, is key to planning for it—and studies like this, he says, highlight just how quickly we’ll all have to adapt.