Dead corals off Malaysia's Tioman island in the South China Sea. A new report has found 14 percent of the world's corals were lost in the 10 years until 2018, much of it due to global warming [File: David Loh/Reuters]

Jakarta, October 6 (RHC)-- Global warming helped wipe out 14 percent of the world’s coral reefs between 2009 and 2018, the largest-ever survey of coral health has found, warning that more of the vibrant underwater ecosystems were likely to die if oceans warm further.

Corals in South Asia and the Pacific, around the Arabian Peninsula, and off the coast of Australia, were the hardest hit, according to the report which was released on Tuesday, compiled by more than 300 scientists in the Global Coral Reef Monitoring Network.

The report spanned data for 40 years, 73 countries and 12,000 sites and found the total area destroyed equal to about 11,700 square kilometres (4,517 square miles).  “Climate change is the biggest threat to the world’s reefs,” co-author Paul Hardisty, the chief executive of the Australian Institute of Marine Science, said in a statement.

Coral reefs cover only 0.2 percent of the ocean floor, but they are home to at least a quarter of all marine animals and plants.  Besides anchoring marine ecosystems, they also provide food, protection from storms and shoreline erosion and jobs for hundreds of millions of people worldwide.

The study looked at 10 coral reef-bearing regions around the world and found that reef loss was mainly the result of coral bleaching, but also overfishing, unsustainable coastal development and declining water quality.  “There are clearly unsettling trends toward coral loss, and we can expect these to continue as warming persists,” Hardisty said.

Oceans absorb more than 90 percent of the excess heat from greenhouse gas emissions and bleaching takes place when corals, under stress from warmer water, expel the colourful algae living in their tissues and turn white.

A single so-called bleaching event in 1998 caused by warming waters wiped out 8 percent of all corals.   “Since 2009 we have lost more coral worldwide than all the living coral in Australia,” noted UNEP Executive Director Inger Andersen.  “We can reverse the losses, but we have to act now.”

The UN’s climate science advisory panel, the IPCC, projects with “high confidence” that global warming of 1.5C above preindustrial levels will see between 70 and 90 percent of all corals disappear.  In a 2C world, less than 1 percent of global corals would survive.   Earth’s average surface temperature has already increased by 1.1C above that benchmark.  

The report titled: Status of Coral Reefs of the World: 2020, found reasons for cautious optimism.  “Some reefs have shown a remarkable ability to bounce back, which offers some hope for the future recovery of degraded reefs,” Hardisty said.

East and Southeast Asia’s so-called Coral Triangle, which contains nearly 30 percent of the world’s coral reefs, were hit less hard by the warming waters and in some cases showed recovery.

This resilience could be due to species unique to the region, potentially offering strategies for boosting coral growth elsewhere, the authors said.