The world’s coral reefs are in the throes of a global bleaching event caused by extraordinary ocean temperatures, the National Oceanic and Atmospheric Administration and international partners announced Monday.
It is the fourth such global event on record and is expected to affect more reefs than any other. Bleaching occurs when corals are stressed so much that they lose the symbiotic algae they need to survive. Bleached corals can recover, but if the water surrounding them is too warm for too long, they die.
Coral reefs are vital ecosystems: limestone cradles of marine life that nurture an estimated quarter of the ocean’s species at some point in their life cycle, support fish that provide protein for millions of people, and protect coastlines from storms. The economic value of the world’s coral reefs has been estimated at $2.7 trillion annually.
“This is scary because coral reefs are so important,” said Derek Manzello, the coordinator of NOAA’s Coral Reef Watch program, which monitors and predicts bleaching events.
The news is the latest example of climate scientists’ alarming predictions that will come true as the planet warms. Despite decades of warnings from scientists and pledges from leaders, nations are burning more fossil fuels than ever before and greenhouse gas emissions continue to rise.
Significant coral die-off has been confirmed around Florida and the Caribbean, particularly among species of coral and olive horn, but scientists say it is too early to estimate the extent of global mortality.
To determine a global bleaching event, NOAA and a group of global partners, the International Coral Reef Initiative, use a combination of sea surface temperatures and evidence from reefs. According to their criteria, all three ocean basins that host coral reefs – the Pacific, Indian and Atlantic – must undergo bleaching within 365 days, and at least 12 percent of the reefs in each basin must be exposed to temperatures that cause bleaching.
Currently, more than 54 percent of the world’s coral cover has experienced bleaching-level heat stress in the past year, and that number is increasing by about 1 percent a week, Dr. Manzello said.
He added that within a week or two, “this event is likely to be the most extensive global bleaching event on record.”
Each of the three previous global bleaching events has been worse than the last. In the first, in 1998, 20 percent of the world’s reef areas experienced bleaching-level heat stress. In 2010 it was 35 percent. The third lasted from 2014 to 2017 and affected 56 percent of the reefs.
The current event is expected to be shorter-lived, Dr Manzello said, because El Niño, a natural climate associated with warmer oceans, is waning and forecasters predict a cooler La Niña period will take place by the end of the year.
Bleaching has been confirmed in 54 countries, territories and local economies, including Florida, Saudi Arabia and Fiji. The Great Barrier Reef in Australia is experiencing what appears to be the most severe bleaching event yet. about one-third of reefs surveyed from the air showed a prevalence of very high or extreme bleaching, and at least three-quarters showed some bleaching.
“Sometimes I get depressed because the feeling is, ‘Oh my God, this is happening,'” said Ove Hoegh-Guldberg, a professor of marine studies at the University of Queensland who published early predictions about how devastating global warming would be. . for coral reefs.
“Now we’re at the point where we’re in the disaster movie,” he said.
The most recent confirmation of the widespread bleaching that prompted Monday’s announcement came from the Western Indian Ocean, including Tanzania, Kenya, Mauritius, the Seychelles and off the west coast of Indonesia.
Swaleh Aboud, a coral reef scientist at CORDIO East Africa, a non-profit research and conservation group based in Kenya that focuses on the Indian Ocean, said coral species known to be heat-resistant are bleaching, as are reefs in colder area considered to be a climate refuge.
He recently visited a fishing community in Kenya called Kuruwitu that has worked to revitalize its reef. Many of the restored coral colonies had become black and white. Others were pale, obviously on their way.
“Urgent global action is needed to reduce future bleaching events, mainly due to carbon emissions,” Mr Aboud said.
Scientists are still learning about corals’ ability to adapt to climate change. Efforts are being made to breed corals that tolerate higher temperatures. In some places, including Australia and Japan, corals appear to be migrating poleward, beginning to occupy new places. But scientists say several factors, such as how much light penetrates the water and the topography of the seafloor, make such migration limited or unlikely in much of the world. In addition, there is the problem of ocean acidification. as seawater absorbs carbon dioxide from the atmosphere, it becomes more acidic, making it harder for corals to build and maintain reefs.
Dr. Hoegh-Guldberg, who has studied the impact of climate change on coral reefs for more than three decades, was the author of a 2018 report by the Intergovernmental Panel on Climate Change that found the world would lose the vast majority of its coral reefs at 1.5 degrees Celsius and almost all at 2 degrees. The nations’ current commitments put the Earth on track for about 2.5 degrees by 2100. But he hasn’t given up hope.
“I think we’re going to solve the problem if we stand up and fight to solve the problem,” Dr Hoegh-Goldberg said. “If we keep paying lip service but don’t follow through with the solutions, then we’re kidding ourselves.”
