If rising seas cause the U.S. coastal housing market to dive — or, as many economists warn, when — the beginning might look a little like what’s happening in Bal Harbour, a glittering community on the northernmost tip of Miami Beach.

With single-family homes selling for an average of $3.6 million, Bal Harbour epitomizes high-end Florida waterfront property. But around 2013, something started to change: The annual number of homes sales began to drop — tumbling by half by 2018 — a sign that fewer people wanted to buy.

Prices eventually followed, falling 7.6% from 2016 to 2020, according to data from Zillow, the real estate data company. All across Florida’s low-lying areas, it’s a similar story, according to newly published research. The authors argue that not only is climate change eroding one of the most vibrant real estate markets in the country, it has quietly been doing so for nearly a decade.

Starting in 2013, sales in safer areas kept climbing but sales in vulnerable ones began to fall. By 2018, the last year for which the paper’s lead author Benjamin Keys and his co-author Philip Mulder obtained data, sales in vulnerable areas trailed safer areas by 16% to 20%. “The downturn started in 2013, and no one noticed,” said Keys, a professor of real estate and finance at the University of Pennsylvania’s Wharton School. “It means that coastal housing is in more distress than we thought.”

The idea that climate change will ruin the value of coastal homes is neither new nor controversial. In 2016, the then-chief economist for the federal mortgage giant Freddie Mac warned that rising seas “appear likely to destroy billions of dollars in property and to displace millions of people.” By 2045, more than 300,000 existing coastal homes will be at risk of flooding regularly, the Union of Concerned Scientists concluded in 2018.

Not everyone was convinced. Oren Alexander, a broker at Douglas Elliman Real Estate in Miami, said every part of the country faces climate threats. “Hurricanes have reached New York City. California is burning,” he said. “I’ll tell you firsthand from working with buyers, are they concerned with sea level rise? No.”