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 percent 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. “The risk of coral reef collapse is escalating, but this must be a wake-up call rather than a cause for despair," said Mishal Gudka, the scientific lead of the global IUCN Red List of Coral Reef Ecosystems assessment, the first of its kind. “Coral reefs have shown a remarkable ability to bounce back from devastating bleaching events,” he said. “Pockets of