Nearly all of the world's shallow-water coral reefs face an extremely high risk of collapse by 2075, with climate change being the greatest threat, the International Union for Conservation of Nature (IUCN) warned on Thursday.

In the first systematic survey of the world's 127 tropical and subtropical coral reef systems, the IUCN said 96% were critically endangered, which is its highest risk category.

Shallow-water reefs are colorful coral ecosystems found at depths of up to around 40 meters (131 feet), and are home to a high level of biodiversity.

Among the reefs affected are Australia's Great Barrier Reef , the Coral Triangle in the western Pacific and Southeast Asia, the Mesoamerican Reef System and the reefs in the Red Sea.

"Heat stress from climate change is the single most consistent threat driving coral reef decline worldwide," the IUCN said when it presented the study at the United Nations' COP17 biodiversity summit in Yerevan, Armenia.

Coral reefs are home to a high level of biodiversity Image:…