The world's coral reef ecosystems almost all face a high risk of collapse in the next 50 years mostly due to warming oceans and heat waves, according to a global assessment released Thursday.

The International Union for Conservation of Nature's assessment, announced on the sidelines of a U.N. biodiversity conference in Albania, found that 96% of shallow-water reef systems are already critically endangered and could disappear by 2075.

Most of the world's famous reef systems - including the Great Barrier Reef in Australia, the Coral Triangle in the Western Pacific Ocean and Southeast Asia, the Mesoamerican Barrier Reef System and the Red Sea coral reefs - are all critically endangered, the highest level of threat.