The planet lost about 14% of its coral reefs between 2009 and 2018, a startling figure that reflects the dire threats to the iconic creatures as climate change continues to ravage sensitive ecosystems around the globe.
A new report, released Monday by the Global Coral Reef Monitoring Network, found mass coral bleaching events linked to warmer temperatures remained the greatest threat to sensitive reefs. The study is the largest analysis of global coral reef health ever done, and includes observations along reefs in more than 70 countries over the last 40 years.
That 14% figure is staggering. Effectively, the loss amounts to about 4,500 square miles of reef, or more than all of the living coral off the coast of Australia, including the iconic Great Barrier Reef.
“There are clearly unsettling trends toward coral loss, and we can expect these to continue as warming persists,” Paul Hardisty, the head of the Australian Institute of Marine Science, said in a statement Monday. “A clear message from the study is that climate change is the biggest threat to the world’s reefs, and we must all do our part by urgently curbing global greenhouse gas emissions and mitigating local pressures.”
In some good news, the report found that reefs still remain resilient even amid the ongoing assault by climate change. If immediate steps are taken to dramatically reduce carbon emissions and rein in climate change, they can recover. Also, global reef cover has increased in some years after mass bleachings.
World leaders are preparing to meet later this month at the United Nations’ COP26 climate change summit, where they are expected to hash out emissions reduction targets for the end of this decade. A report released by the UN in August found the burning of fossil fuels had essentially locked in intensive climate change for the next 30 years, a statistic the body’s secretary-general called a “code red for humanity.”
Aside from their beauty, coral reefs are iconic, essential structures that provide an outsized boon to the oceans and humans that live near them. Reefs cover just 0.2% of the ocean floor, but account for at least 25% of the ocean’s biodiversity. The report estimates reefs provide about $2.7 trillion in value per year, including some $36 billion in tourism.
But reefs are particularly vulnerable to climate change. Warmer waters linked to the phenomenon can effectively cook the delicate corals during a process known as bleaching. When that happens, the once-colorful reefs turn bone white as the algae that feeds them leaves their skeletons. If temperatures stabilize, the corals can recover, but if the hot water lingers too long large stretch can die. Bleached reefs take years to recover, but frequent bleaching events can kill them off for good.
The threat is notably pressing in Australia. The Great Barrier Reef has suffered a devastating series of mass coral bleaching events that have left large swaths of the emblematic structure dying or dead. UNESCO said in June the World Heritage Site should be listed as “in danger,” citing the ongoing threat of climate change, but the Australian government successfully lobbied to delay that decision, which would have been a significant blow to the country’s identity.
The devastation hasn’t been confined to Australia. One mass coral bleaching event that impacted the entire globe in 1998 killed 8% of the planet’s corals, mainly in the Indian Ocean, Japan and the Caribbean. However, reefs had time to recover after that mass bleaching event and largely bounced back.
Now, the oceanic heat waves are happening too often in some regions for reefs to heal. Along the Great Barrier Reef, mass bleaching events have struck three times in five years.