The key facts
- IUCN assessed coral reefs globally for the first time: 96% were classified as being in a 'critical' category
- The assessment is based on a warming scenario of 2.7°C by 2100; without future projections, only 24% of reefs would be classified as critical
- 63% of reef ecosystems are threatened by overfishing; the list includes the Great Barrier Reef, the Coral Triangle, the Mesoamerican Barrier Reef and Red Sea reefs
Almost all of the world's reefs are under threat
The International Union for Conservation of Nature (IUCN) warned on Thursday, October 22, that almost all of the world's shallow-water coral reefs will face an 'extremely high risk' of destruction by 2075 due to climate change. In the first assessment of its kind, the organization, which maintains the world list of endangered species, classified 96% of the planet's coral reef systems in the highest risk category — 'critical'.
Methodology and scope of the analysis
The researchers used a 'middle' scenario from the UN panel of climate experts, assuming a rise in global temperature of 2.7°C above pre-industrial levels by 2100. The day before, the UN warned that under current emissions reduction commitments the world is heading toward 2.6°C of warming this century. The IUCN analysis covered 127 tropical and subtropical coral systems covering 188,362 square kilometers.
Main threats
'Heat stress from climate change is the most persistent threat driving the degradation of coral reefs worldwide,' IUCN said. Corals are sensitive to temperature and particularly vulnerable to human-caused ocean warming, which makes destructive bleaching events more frequent and severe. Overfishing also harms corals: excessive harvesting of parrotfish and groupers threatens 63% of reef ecosystems, as these species control algae and maintain ecological balance. Other threats include coastal construction, pollution, tourism and increasingly frequent storms.
Largest reefs on the critical list
The 'critical' category includes the world's largest and most biodiverse reefs: Australia's Great Barrier Reef, the Coral Triangle in Southeast Asia and the western Pacific, the Mesoamerican Barrier Reef System in the Caribbean, and the coral reefs of the Red Sea. A reef ecosystem is considered destroyed when the hard corals that form its living foundation largely disappear and are replaced by algae, rubble and sponges.
Not all is lost, IUCN says
Despite the warning, IUCN noted that reefs in most regions of the world are 'not yet lost.' If only events of the past 50 years are taken into account, without future climate projections, 24% of ecosystems would be classified as critical instead of 96%. 'It is not too late to give coral reefs a chance to recover, but decisive action against climate change and a halt to further ocean warming are required,' said IUCN Director General Grethel Aguilar. According to her, ambitious emissions reductions, strengthened protection and restoration, as well as sustainable investment in coastal ecosystems and the communities that depend on them, are needed.
Context and scientists' reaction
Mishal Gudka, scientific lead of the IUCN Red List assessment of reef ecosystems and also research director of the organization CORDIO East Africa, called the situation 'a wake-up call, not a cause for despair': 'Coral reefs have demonstrated a remarkable ability to recover from devastating bleaching events.' The report was released during the UN biodiversity summit COP17 in Yerevan, where governments are under pressure over fulfilling the agreement to halt and reverse biodiversity loss by 2030. Last week, a study published in the journal Nature found that by 2020 nearly half of coral species had an 'elevated relative risk of extinction,' with climate change as the main driver.
