If average global temperatures rise just three degrees above pre-industrial temperatures, melting glaciers and ice sheets will push up the sea level enough to inundate 136 sites considered by UNESCO (United Nations Educational, Scientific and Cultural Organization) to be cultural and historical treasures, sometime within the next 2,000 years, reports a new study published this week inEnvironmental Research Letters.
The researchers said they didn't try to pinpoint the exact timing of rising sea levels. And while 2,000 years sounds like a big window, some of UNESCO's 700 World Heritage sites are older than that, they point out.
"The fact that tides and storm surges could already affect these cultural sites much earlier, has not even been taken into account," lead author Ben Marzeion said in a statement.
The list of threatened World Heritage Sites includes four in Canada:
- L'Anse aux Meadows National Historic Site in Newfoundland.
- Old Town Lunenburg in Nova Scotia.
- Sgang Gwaay in B.C.
Marzeion, a climate scientist at the University of Innsbruck in Austria, and Anders Levermann from the Potsdam Institute for Climate Impact Research in Germany, said they chose in their study to look 2,000 years in the future to a point when sea levels would have stabilized and there would be no additional melting.
"The physical processes behind the global rise of the oceans are gradual, but they will continue for a very long time," Marzeion said.
Levermann noted that the average global temperature has already risen 0.8 degrees compared with pre-industrial levels. Even if the temperature doesn't rise any further, the study predicts that 40 World Heritage Sites will still end up below sea level in coming centuries.
In its most recent report, released last September, the United Nations Intergovernmental Panel on Climate Change predicted that the global average temperature would rise by 0.3 to 4.8 degrees by the end of the century, depending on whether greenhouse gas emissions are cut drastically or continue to increase. The panel expects the average sea level to rise by 26 to 82 centimetres.
In the new study, the researchers combined four sets of climate simulations that calculated the average sea level would rise 2.3 metres for every degree that the global average temperature increases.
However, the rise is expected to vary by region, due largely to changes in the gravitational pull of mountains and ice caps on the water, as well as the fact that some coastal land areas are rising and others falling over time.
The researchers calculated the regional sea level at different World Heritage Sites 2,000 years from now for different average global temperatures. They used that to determine how much global temperatures would have to increase before each site would be underwater.
"If we do not limit climate change," Marzeion concluded, "the archeologists of the future will need to search for major parts of our cultural heritage in the oceans."
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