Undersea forests, bleached and killed by rising ocean temperature, might disappear in a few decades, experts warn
Global heating and ocean acidification have already severely bleached 16 to 33% of all warm-water reefs, but the remainder are vulnerable to even a fraction of a degree more warming, said David Obura, chair of the Coral Specialist Group in the International Union for the Conservation of Nature.
“It will be like lots of lights blinking off,” he told the Observer. “It won’t happen immediately but it will be death by 1,000 blows. Between now and 2 degrees Celsius, we will see more reefs dropping off the map.”
Obura added: “Children born today may be the last generation to see coral reefs in all their glory. Today’s reefs have a history going back 25 million to 50 million years and have survived tectonic collisions, such as that of Africa into Europe, and India into Asia. Yet in five decades we have undermined the global climate so fundamentally that in the next generation we will lose the globally connected reef system that has survived tens of millions of years.”
The warning follows a landmark UN climate report that upgraded risk assessments for corals following faster-than-expected global bleaching. Scientists on the Intergovernmental Panel on Climate Change (IPCC) warned that if warming reached 2C, currently very likely in the next 50 years, there would be a more than 99% chance that tropical corals would be eradicated.
“Most available evidence suggests that coral dominated ecosystems will be non-existent at this temperature or higher,” said the IPCC study, which was approved by all 195 nations in the UN last month.
As well as losing one of the most beautiful and biodiverse habitats on earth, the UN report warned of severe knock-on impacts to fisheries and millions of people living in coastal communities, who will lose vital sources of income and be less protected from storms.
Corals are often described as undersea forests, but they are declining far more quickly than the Amazon. Along with the Arctic and high-mountain landscapes, the reefs – which have evolved over hundreds of millions of years – are likely to be among the first ecosystems to be wiped out by the climate crisis. A temperature rise of just 1 to 2C can trigger an evacuation of the algae upon which corals depend, draining them of colour and making the structure more brittle. These bleaching events can be temporary if waters cool, but the more frequent they are and the longer they last, the greater the risk of irreparable damage.
But that is exactly what is happening. Bleaching was first observed in 1983. It was seen on a global level in 1998, then 2010, then for three consecutive years from 2015 to 2017.
“Coral bleaching events are growing so severe and so frequent around the planet that reef systems are fragmenting into isolated pockets,” said Obura. “Some of these will undoubtedly survive this century, but the highest scientific evidence tells us that, unless we do everything to limit warming to 1.5C, we will lose 99% of the world’s coral reefs in coming decades.”
Eleven of the 29 World Heritage reefs have already suffered bleaching. On current trends, UNESCO predicts this will rise to 25 by 2040.
More widely, at highest risk are reefs off of Saudi Arabia, Madagascar, Hawaii and Papua New Guinea, which are likely to suffer bleaching long before the global average 2043. Those with a greater – though still slim – prospect of survival may be off of Egypt, Australia (including the Great Barrier Reef), Cuba, Indonesia and the Philippines.
But there are other threats beyond warming and acidity. Off the Philippine island of Palawan, once pristine reefs have been badly damaged by sewage run off from tourists resorts, pollution from boats and reckless fishing, including the pumping of cyanide into the coral structure to stun fish that float out and get scooped up and sold off for Chinese home aquariums.
According to Vince Cinches, Oceans Campaigner of Greenpeace Southeast Asia, it is a calamity that this is happening in the Coral Triangle, which ought to be a refuge because it is one of the ocean regions most resilient to climate change “Even in the Philippines, we are fast losing our coral,” he said. “We need to reduce stress from overfishing, coastal development, pollution, mining, tourism and climate change.”
Although some conservationists are risking their lives to prevent this, economic pressures continue to grow and chances of coral survival are slim. The IPCC report noted that even if temperatures were held to 1.5C, between 70% and 90% of reefs would be lost.
A few of the more than 800 coral species have already been declared extinct, but as long as the major reef builders continue to exist, there is a faint possibility that this complex systems can be rebuilt if temperatures stabilise.
Scientists like Obura are increasingly turning to advocacy rather than just observation, but they say the last great function of corals might be to teach humanity to care better for other ecosystems.
“I’m of a generation of scientists watching them disappear. It’s very depressing,” he said. “Above 1.5C, in about 50 years, they will be ecosystems of legend, with beautiful virtual recreations and a treasure of historic, fantastic movies and images, but very little to see in real life.”
“We are trying to do more than record the decline by making activist statements. We need to get the message out that we must stop this happening to other eco-systems. That’s what motivates me. If we don’t take this lesson to restrict warming, then we’ll face much more of an impact.”
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