Hundreds of the world's most precious natural and cultural sites, including the Great Barrier Reef, Mount Kilimanjaro and Venice, are under threat from climate change, a UN report warned today.

Rising sea levels, increased flooding risks and depleted marine and land biodiversity could have disastrous effects on the 830 designated Unesco world heritage sites, the study said. "The international community now widely agrees that climate change will constitute one of the major challenges of the 21st century," Koichiro Matsuura, the director general of Unesco, said in a foreword to the report.

"[Its] impact on the world's cultural and natural heritage is also a subject of growing concern." Unesco researchers said 70% of the world's deep sea corals could be in danger from changing conditions related to rising temperatures and increased oceans acidification by 2100.

The Great Barrier Reef, in Australia, is likely to suffer frequent bleaching outbreaks - cases in which corals turn white and may die because of rising sea temperatures - putting its fish population under threat. Melting glaciers in the Himalayas and Africa are also likely to wipe out rare species, the report said. The habitat of the rare snow leopard in Sagarmatha (Everest) national park in Nepal is at risk, and human settlements are threatened by catastrophic flooding from glacial lake surges.

Three of London's world heritage sites - the Palace of Westminster, the Tower of London and the riverbank buildings of Maritime Greenwich - face a significant threat from "more intense and frequent flooding" of the River Thames, the Unesco report warned.