YEREVAN, Armenia (AFP) — Nearly all of the world’s shallow-water coral reefs face an extremely high risk of collapse by 2075 due to climate change, the International Union for Conservation of Nature (IUCN) warned Thursday.

In the first global assessment of its kind, the world authority on threatened wildlife classified 96 per cent of the planet’s coral reef systems as “critically endangered” — its highest risk category.

Corals are heat sensitive and particularly vulnerable to human-driven climate change, which is warming the world’s oceans and increasing the frequency and intensity of damaging bleaching events.

“The future threat of climate change is looming and severe, and that poses a very high risk to the survival of these ecosystems,” said Mishal Gudka, scientific lead of the IUCN Red List of Coral Reef Ecosystems assessment.

The emergence this year of a “super” El Nino, the natural warming phenomenon, also presents a risk to corals, Gudka said at a news conference at the UN’s COP17 biodiversity summit in Yerevan, Armenia.

The IUCN presented its findings at COP17, where governments are under pressure to make progress on a landmark pact to halt and reverse biodiversity loss by 2030.

For its assessment, the IUCN used the “middle-of-the-road” scenario from the UN’s panel of climate experts that projects global temperatures rising 2.7C above pre-industrial levels by 2100.

The world is on track for 2.6C warming this century under current global commitments to cut planet-heating emissions, the United Nations warned Wednesday.

“Heat stress from climate change is the single most consistent threat driving coral reef decline worldwide,” the IUCN said in a statement.

Overfishing is also hurting corals as certain herbivores and predators help control algae and maintain an ecological balance, the organisation said.

The overexploitation of parrotfish and other groupers threatens 63 per cent of coral reef ecosystems.

Coastal development, pollution, tourism and more frequent storms are among other threats.