Most people check out Zillow, a popular online real estate app, for information on how many beds and baths a house includes, or the quality of local schools, or how long a home has been on the market.

But climate experts at the Union of Concerned Scientists (UCS) saw Zillow as just the kind of big data needed to better inform assessments of the risks of flooding to properties around the nation’s rim. And looking at the app through that screen, they have turned up some troubling visions.

Property losses in the United States could run into the hundreds of billions of dollars unless rapid action is taken to bring climate change under control, they warned in a study released Monday.

The owners of more than 150,000 existing homes and commercial properties, worth $63 billion, could find their assets at risk from repeated flooding in the coming 15 years. That risk could double by 2045.

“This is, of course, homes that are often people’s single biggest assets,” said Rachel Cleetus of the UCS. “This is about entire communities that might find much of the property in their community gets inundated, and that might affect their community tax base.”

By the end of the century, if seas rise by 6.6 feet—a high, but not worst-case projection in the 2017 National Climate Assessment—the damage could be staggering.

More and more houses will be hit by more and more floods, some so frequently that they are essentially not fit to live in.

More Homes at Risk of Chronic Flooding

The study focused on properties at risk of chronic flooding, which it defines as flooding at least 26 times a year.

If sea level rises more than 6 feet by the end of the century, UCS estimated that the homes of more than 4.7 million people will be at risk of chronic flooding. With commercial properties included, that’s more than $1 trillion in value, and it doesn’t take into account future development or rising property values.

Even with 4 feet of sea level rise, the homes of more than 2 million people, plus many commercial properties, are likely to face chronic flooding.

If global warming is controlled in line with the goals of the Paris climate agreement, sea level rise and the damage it causes would be less. To lessen the impact, greenhouse gas emissions would have to be brought to zero within a few decades, scientists say.

‘A Lot of People Are Unaware of What’s Coming’

“Coastal real estate markets currently, for the most part, are not reflecting this risk,” Cleetus said. “A lot of people are unaware of what’s coming, and that is cause for deep concern.”

Andrew Teras of Breckinridge Capital Advisors, which specializes in municipal bonds, said investors should heed the implications for property values and property taxes.

The risks are not faced exclusively by thriving communities and wealthy individuals with seaside houses. In Norfolk, Virginia, for example, businesses and a variety of neighborhoods, including a large public housing development, already face frequent nuisance flooding, and officials are trying to figure out how to protect as much of the city as they can. 

Low-Income Communities at Risk

Nearly 175 communities nationwide could see 10 percent or more of their housing stock at risk of chronic flooding by 2045 if seas keep rising under the high sea level rise scenario. Nearly 40 percent of them are low-income communities with poverty levels above the national average.

Rob Moore, a senior policy analyst with the Natural Resources Defense Counsel who was not involved in the current study, said the focus on low-income communities is often overlooked in discussions about sea level rise.

“Many people immediately think this is just affecting affluent people who live at the beach,” he said. “They don’t understand that this type of flooding affects areas further inland, and often lower-income communities.”

Low-income families are harder hit by flood damage because a higher percentage of their assets are tied up in their homes, he said.

“If you are wealthy, you own a house, you have probably a pretty robust stock-and-bond portfolio, you might have a second house or even a third house, you have automobiles, you have things that you have equity in,” he said. “For a lower-income person, often times the only thing of real value they own is their house.” 

Because Zillow tracks current market values but does not make forecasts, the study did not take into account additional coastal developments or future changes in property value. Nor did it factor in any climate adaptation measures such as new sea walls or the impact of major storms.