Almost all of the world’s shallow-water coral reefs are at risk of collapse by 2075, with climate change the biggest threat.

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 per cent 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.