LONDON: Climate change is threatening the world's cultural heritage with scientists estimating that 136 of 700 listed cultural monuments by Unesco will soon be under water.

A new study by Ben Marzeion from the University of Innsbruck and Anders Levermann from the Potsdam Institute for Climate Impact Research said that from the Statue of Liberty in New York to the Tower of London and the Sydney Opera House -- sea-level rise will not only affect settlement areas but also numerous world heritage sites listed by Unesco.

The monuments are in Unesco's World Heritage List.

Nearly one-fifth of world cultural heritage sites would be affected by global warming of a further three degrees Celsius, they said.

If global average temperature increases by just one degree Celsius more than 40 of these sites will be threatened by the water during the next 2000 years.

With a temperature increase of three degrees, about one fifth of the cultural world heritage will be affected in the long term.

"Around 136 sites will be below sea-level in the long-run in that case if no protection measures are taken," Marzeion said. "The fact that tides and storm surges could already affect these cultural sites much earlier has not even been taken into account," he added.

Among the world heritage sites affected are the historical city centres of Bruges, Naples, Istanbul and St Petersburg and a number of sites in India and China.

"If large ice masses are melting and the water is dispersed throughout the oceans, this will also influence the Earth's gravitational field," Levermann said.

"Sea-level rise will therefore vary between regions," he added.

They calculated future sea-level rise for all world regions and compared these projections with today's coastal settlement areas and the sites of the cultural world heritage. "Our analysis shows how serious the long-term impacts for our cultural heritage will be if climate change is not mitigated," Levermann said.

"The global average temperature has already increased by 0.8 degrees compared to pre-industrial levels. If our greenhouse-gas emissions increase as they have done in the past, physical models project a global warming of up to five degrees by the end of this century".

The physical processes behind the global rise of the oceans are gradual, but they will continue for a very long time," says climate scientist Ben Marzeion.

"This will also impact the cultural world heritage".

Apart from historical cultural monuments, regions that are currently populated by millions of people would be affected. Twelve countries around the world could lose more than half of their present land area and about 30 countries could lose one tenth of their area if temperatures rose by three degrees.