Illustration: Sarah Grillo/Axios

Sea level rise due primarily to global warming threatens to submerge dozens of the most culturally significant sites in the Mediterranean.

  • In Italy alone, at least 13 UNESCO World Heritage Sites are at risk, according to a study published this week in Nature Communications.

Why it matters: UNESCO designates cultural World Heritage Sites for places that represent cultural traditions or civilizations that have since disappeared. The Mediterranean region was home to several ancient civilizations, many of which flourished by the sea.

"Mediterranean society has been centered on the coast and sea for millennia. Much of the cultural heritage is therefore in the hazard zone,"
— Richard Tol, study co-author and professor at the University of Sussex

What they did: For the study, a team of researchers in Europe produced the first-ever risk assessment of cultural UNESCO World Heritage Sites based on flood risk and exposure to erosion.

  • They defined the flood risk as the floodplain of a storm surge with a 100-year return period, and calculated how such flood footprints and frequency would shift depending on different scenarios involving low, medium to high greenhouse gas emissions.
  • The team looked at 49 World Heritage sites located within 10 meters, or 33 feet, above sea level.

What they found: The researchers found that the majority of the 49 World Heritage sites they examined are already at risk from either a 100-year flood level, erosion, or both.

Such risks are only going to increase during the rest of the century, with the sharpest increases occurring if greenhouse gas emissions are not significantly curtailed in the next two decades.

  • Not surprisingly, the World Heritage Site that's at the most risk from sea level rise is Venice and its Lagoon. But costly protective measures are already being put into place there, in the form of a retractable barrier that can protect against high waters of up to 3.6 feet above sea level.
  • World Heritage Sites located in the northern Adriatic Sea are also at high risk of flooding, particularly under a high emissions scenario. This includes the Patriarchal Basilica of Aquileia, in Italy.
  • The country with the most at-risk sites is Italy, with 13, followed by Croatia and Greece.
  • Only 2 sites — Medina of Tunis and Xanthos-Letoon, an archaeological complex in Greece, were found to not be at risk from either flooding or erosion by 2100 under any of the scenarios studied.

The researchers note that adaptation options may be limited, and that expensive solutions — such as the wall being erected around Venice — are not an option for many other sites.

"It is relatively easy to protect a working city, although it may be expensive and the political will may be lacking," Tol told Axios. "Heritage is more difficult as dikes and seawalls may ruin the very thing we seek to preserve."

Go deeper: Catch up with the NYT's project on covering climate change's threat to World Heritage Sites.

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