Climate change threatening more than 40% of the world's corals with extinction, conservation group says

Climate change is decimating the likelihood of survival for a large portion of the world's coral reefs, according to new research.

About 44% of global reef-building coral species are at risk of extinction, according to the International Union for Conservation of Nature's Red List of Threatened Species, a new version of which was released Wednesday amid COP29, the United Nations climate conference, in Baku, Azerbaijan.

The main threats to corals include annual severe bleaching events, pollution and the impacts of disease. Other threats include fishing activity -- especially bottom trawling -- deep-sea mining, drilling for oil and gas, or laying of deep-sea cables, according to the IUCN.

The finding is a sharp increase since 2008, the last time the conservation status of 892 warm-water reef-building coral species were assessed, when about one-third of the species were found to be at risk of extinction, according to the IUCN.

The main driver for the widened scope of risk is global warming, according to researchers, who used the most recent status update of coral reefs from the Global Coral Reef Monitoring Network as well as a projected increase in warming events and major bleaching events for the assessment.

Two examples include the Staghorn coral (Acropora cervicornis) and Elkhorn coral (Acropora palmata), two critically endangered species in the Caribbean that have experienced significant declines due to increased warming, water pollution, hurricanes and the severe impacts of coral diseases, according to the IUCN.

Coral reefs have been experiencing massive health declines in response to unprecedented warm waters in recent years.

In April, the National Oceanic and Atmospheric Administration declared the world's fourth global bleaching event.

A paper published in the Proceedings of the National Academy of Sciences in 2021 found that coral reefs will stop growing in the next decade or so unless a significant reduction in greenhouse gases is achieved. A 2020 World Heritage Outlook report found that the Great Barrier Reef has deteriorated to 'critical' levels due to climate change.

NOAA's Coral Reef Watch predicts a 90% probability of coral bleaching heat stress in the next four months.

Researchers have devised creative solutions aimed at helping the reefs thrive.

In Australia, the world's largest seagrass nursery was unveiled on Wednesday. The installation, located off Gladstone, on the northeast part of the continent, aims to "supercharge" restoration of Great Barrier Reef ecosystems, according to the Great Barrier Reef Foundation.

The purpose-built seagrass restoration nursery will also help to mitigate climate change by potentially storing 400 million tons of carbon -- the equivalent weight of eight Sydney Harbour bridges, according to the foundation.

"As the world grapples with how to meet urgent emissions reduction targets, we are increasingly looking to the ocean and its coastal ecosystems -- which sequester carbon 30-50 times more efficiently than rainforests -- for bridging solutions," said Great Barrier Reef Foundation Coastal Habitat Restoration Director Will Hamill in a statement.

Underwater speakers that play the sounds of a healthy reef, such as fish calls, were found to help coral larvae settle at rates up to seven times higher, according to a study published in Royal Society Open Science earlier this year.

Last year in North Carolina, 15 acres of 3D-printed artificial reef was installed to bolster the region's biodiversity and provide a skeleton for natural reef to grow.

"This is not just about preserving the spectacular beauty of coral reefs," said Beth Polidoro, IUCN Species Survival Commission Coral Red List Authority coordinator. "Coral ecosystems also sustain coastal fishing communities, stabilise the shoreline and coastal habitats, and help remove carbon from the ocean, among other benefits."

But major progress in the reduction of greenhouse gas emissions remains the key to protecting coral reefs and global biodiversity as a whole, according to scientists.

"Climate change remains the leading threat to reef-building corals and is devastating the natural systems we depend on. We must take bold, decisive action to cut greenhouse gas emissions if we are to secure a sustainable future for humanity," IUCN Director General Grethel Aguilar said in a statement.

More research is needed on how corals react to warmer waters, the IUCN researchers said.