Rising water levels due to climate change could deprive Germany of the historic city centres of Hanseatic trading hubs in Lübeck, Bremen, Straslund and Wismar.
That's the conclusion of a new study looking at the potential loss of world heritage worldwide over the next 2,000 years.
Wismar and Stralsund were major trading centres of the Hanseatic League in the 14th and 15th centuries. In the 17th and 18th centuries they became Swedish administrative and defensive centres for the German territories.
Bremen, on the river Weser, would also be threatened by rising water, the study found.
"When thinking about climate change, people usually think about ecological and economic consequences," Ben Marzeion, study author and climate scientist at the University of Innsbruck, told The Local.
"We wanted to add another dimension: what might the cultural impacts be? Culture is hard to quantify, but for the Unesco list there is general agreement that these sites are significant and worthy of special consideration and protection," he explained, adding that Unesco had not funded the study.
Using sea level rise estimates and topographic data, the researchers looked at the impact of rising water levels at UNESCO sites over the next 2,000 years.
"In this time scale, ocean heat content and glacier ice mass can be considered to be in equilibrium with global temperatures, and relatively independent of the warming path of the initial 100 years," wrote the German and Austrian study authors at the University of Innsbruck.
As many as 40 Unesco heritage sites could be affected by rising oceans over the next two millienia if climate change continued at its current rate, they said.
Even more alarming would be the impact of a "not improbable" three-degree Celsius rise in temperature over the same period, which could endanger 136 Unesco sites worldwide.
The study, published in the IOP Science journal, recognized the difficulty of predicting the effects of climate change, and also admitted they had not been able to take local conditions such as localized flash flooding into account.
Still, they said, a failure to act to stem the rise of the water could be disastrous.
"Our analysis illustrates that the spatial distribution of the existing and potential future cultural world heritage makes it vulnerable to sea-level rise," the study authors wrote.
"Future generations will face either loss of these sites, or considerable efforts to protect them," they warned.
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