A draft management plan for the protection of the World Heritage site describes coastal erosion as “a threat to the long-term survival” of the subterranean village.
The report, compiled by Unesco, Historic Scotland, RSPB, Scottish Natural Heritage and Orkney Islands Council, says the site is at “significant risk from a variety of climate-related factors”.
These include: “Increases in storminess and sea level rise and consequent increases in coast erosion; torrential rain and flooding; changes to wetting and drying cycles; and changes to flora and fauna.”
Skara Brae is believed to be between 4,000 and 5,000 years old and is the main attraction of Heart of Neolithic Orkney (Hono), which was made a World Heritage site by Unesco in December 1999. In addition to the village, the site includes Maeshowe, the Ring of Brodgar, the Standing Stones of Stenness and other nearby sites.
Unesco said the monuments “proclaim the triumphs of the human spirit in early ages and isolated places” and “stand as a visible symbol of the achievements of early peoples away from the traditional centres of civilisation”.
For the past 100 years, the main bulwark against serious storm damage and erosion to the village has been a specially erected sea wall. The wall has been undermined by waves over the years and is in need of major repairs, and archaeologists now fear that rising sea levels may prove too much for it.
Alice Lyall, Historic Scotland’s World Heritage Site co-ordinator, said: “It’s done a really good job, but if there is a sea level rise, and there is increased storminess – because it is storm events that concern us in particular – there could be a problem.
“Already, if you have a north-west wind and a high tide, parts of the site can be awash. Luckily, so far it has not been parts of the archaeology, just what used to be a visitor centre hut.”
Julie Gibson, Orkney’s county archaeologist at the University of the Highlands and Islands, said: “There are significant threats and there should be planning to reduce these risks.
“I don’t know how we would manage a big surge from the sea – they are very dangerous because they could suck walls out with them as they retreat.”
Skara Brae was discovered in the 19th century because of severe weather. In the winter of 1850 a storm-battered Orkney and a combination of gale-force winds and extremely high tides stripped the grass from a large mound, then known as “Skerrabra”, revealing the outline of a number of stone buildings.
In 1924 another violent storm swept away parts of the monuments, prompting Edinburgh University academic Professor Vere Gordon Childe to carry out a fuller investigation into the site.
Gibson said it was vital to look at ways of reducing the damage caused by waves, as Skara Brae remains Scotland’s “most vulnerable” historical site.
She said the potential for a “catastrophic” loss through storm damage means Historic Scotland needs to invest in “new heritage” on Orkney.
Gibson said: “Under the dunes, to the south of the excavated remains, there are other parts of the village. We need to continue to protect, but we have to look at alternatives.
“Two hundred years from now it’s entirely possible it [Skara Brae] could be entirely unsustainable – and if we get climate change, and sea levels rise, then it could be sooner than that. We have to look at other sites.”
She said that other Neolithic sites outside the Hono site were under excavation and causing excitement in archaeological circles.
Gibson added that opening up other locations would help spread the tourism load, reducing the impact of traffic through the existing parts and the potential damage that comes with it.
According to the latest figures, 46 per cent of people who visit Orkney each year go to Skara Brae. The number of cruise ships stopping there are increasing each year, making the site integral to the island economy.
Lyall said she believes that the site is being well cared for, but added: ““We can’t say ‘in that case it’s fine we don’t have to keep reassessing’ because things can change.
“We are not resting on our laurels.
“If you went back 25 years you would not get many cruise ships stopping here, but they are increasing year on year, bringing other pressures.”
Conservationists have been forced to undo alterations for tourism in the past. A glass viewing ceiling inserted into the roof on one dwelling during the 1930s had to be closed because it affected the room’s humidity, damaging the stonework.