This photo shows the old town of Dubrovnik from a hill above the city. (Darko Bandic/AP)

The old city of Dubrovnik, clinging to the Croatian coast of the Adriatic Sea, is one major storm away from a flood that could cover 10 percent of a medieval city long known as the “Pearl of the Adriatic” and more recently as a main setting for HBO’s “Game of Thrones.”

It’s one of about 40 treasured historical sites across the Mediterranean, including the winding canals of Venice and the ancient city of Carthage, at risk from rising seas, according to a study published Tuesday in the journal Nature Communications.

The reason for their sweeping vulnerability is the same one that fostered so many civilizations in the Mediterranean to begin with. It’s the lure of the sea, dating back at least to the time of the ancient Phoenicians, who set sail from the now-threatened sites of Byblos and Tyre along the current coast of Lebanon.

“That’s just classic Mediterranean history,” said Joseph Manning, a professor of ancient Greek history at Yale University, who praised the new research. “Everything is within two miles of the coast.”

But now, numerous Roman ruins, the original site of Carthage, historic regions of Istanbul and many other landmarks left by cultures ranging from the Phoenicians to the Venetians could be flooded in extreme storm events, or face growing erosion risks, said the research.

“What surprised me the most is that actually even under current conditions, there are so many World Heritage sites that are at risk,” said Lena Reimann, a researcher at Kiel University in Germany and a lead author of Tuesday’s study.

In a world of rising sea levels, those risks will grow only more severe, threatening the destruction of irreplaceable cultural landmarks.

“We cannot put a value on what we will lose” if action isn’t taken to protect such sites, Reimann said. “It’s our heritage — things that are signs of our civilization. It cannot really be put in numbers. It’s more an ethical question, a moral question. We will not be able to replace them once they are lost.”

The study used the database of UNESCO World Heritage sites and projections of future sea level to arrive at its conclusions. It found that out of 49 total such sites along the coasts of the Mediterranean, 37 are already vulnerable to a 100-year storm surge event.

Many of the most at-risk sites were along the Adriatic Sea and included not only Venice but also the early Christian monuments of Ravenna, and the archaeological area and patriarchal basilica of Aquileia.

A closer look at the archaeological area at Aquileia gives a hint of just how much is at stake. Here, according to UNESCO, an ancient city “still lies unexcavated beneath the fields, and as such it constitutes the greatest archaeological reserve of its kind.” In other words, a historical site that hasn’t even been uncovered yet could be damaged or lost.

For Yale’s Manning, rising seas could be the next destroyer of human culture to come along after massive losses in the past decade alone tied to violence and civil war in Syria, Iraq and Egypt, among other countries.

“In terms of cultural heritage in the last decade, it’s shocking. It’s alarming and depressing,” he said.

The largest number of vulnerable sites, the study found, were located in present-day Italy. Croatia, Greece and Tunisia also have a large number of sites within their present borders.

The risk only increases as sea level rises for these sites, and the study calculated an additional, related erosion risk at 42 of them. This, too, will worsen.

The central reason for so much vulnerability, the research notes, is simply that human civilizations, as they emerged in the Mediterranean (and elsewhere), have traditionally clustered near water. It offers many advantages, ones quickly exploited by the far-ranging Phoenician sailors and numerous other local cultures.

The problem is that while sea level rise has been slow for the past 3,000 years, it has accelerated over the past century as human-driven climate change has commenced. The 21st century is projected to outdistance the last 100 years by a large margin.

Reimann said a handful of places — including Venice, which is putting in place a mobile barrier system to help guard against floodwaters — have poured time and money into finding ways to adapt. But such sites are in the minority.

"We couldn’t really find any other examples across the whole Mediterranean region where adaptation measures were pursued as much as in Venice,” Reimann said.

National governments are charged with caring for World Heritage sites. But Reimann said that although there are regionwide sustainability efforts, those policies don’t deal specifically with vulnerable cultural sites.

“When you go over the management plans, there are just a few that mention sea-level rise as a threat,” she said, adding, “There are many sites where adaptation is urgently needed.”

The United Nations itself has recognized the precarious nature of many heritage sites amid the changing climate, saying that “their continued preservation requires understanding these impacts,” as well as “responding to them effectively."

Over the dozen years, UNESCO has studied the potential effects of climate change on historic sites and put together guidance for people managing specific sites on how to make them more resilient. In 2014, it published a guide. Using both theoretical examples and real-life case studies, the guide offers site managers a road map for how to plan for climate change.

“Climate change is not a passing trend — it is here to stay, and it will impact all landscapes, including all natural World Heritage sites, fundamentally changing the way we understand and manage them,” the guide reads. It adds, “What is clear is that change is on the way.”

The research, in the end, adds a new guise to sea-level rise, which has been traditionally discussed in terms of how it is affecting people’s present-day homes and modern cities, not ancient ones. But perhaps those two narratives aren’t so different.

“The [sites] that the UNESCO has declared as cultural heritage are the ones of the past. We are currently building the cultural heritage of the future in our cities and coastal areas,” said Anders Levermann, an expert on sea-level rise at the Potsdam Institute for Climate Impact Research in Germany, who was not involved in the study. “And if we have to abandon these eventually because of the flood risk or because they’re simply really under the sea level, that will be a tremendous loss.”