The world's coral reefs are in the midst 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 global event of its kind on record and is expected to affect more reefs than any other. Bleaching occurs when corals become so stressed that they lose the symbiotic algae they need to survive. Bleached corals can recover, but if the water around them is too warm for too long, they die.
Coral reefs are vital ecosystems: limestone cradles of marine life that nourish a quarter of ocean species at some point in their life cycles, 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 a year.
“This is scary, because coral reefs are so important,” said Derek Manzello, 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 coming true as the planet warms. Despite decades of warnings from scientists and promises from leaders, nations are burning more fossil fuels than ever and greenhouse gas emissions continue to rise.
Substantial coral die-off has been confirmed in Florida and the Caribbean, particularly among staghorn and elkhorn species, but scientists say it is too early to estimate what the extent of the global mortality will be.
To determine a global bleaching event, NOAA and global partner group the International Coral Reef Initiative use a combination of sea surface temperatures and evidence from reefs. Under their criteria, the three ocean basins that host coral reefs (the Pacific, Indian and Atlantic) must experience bleaching within 365 days, and at least 12 percent of the reefs in each basin must be subject to temperatures that cause whitening.
Currently, more than 54 percent of the world's coral area has experienced bleaching-level heat stress in the past year, and that number is increasing about 1 percent per week, Dr. Manzello said.
He added that within a week or two, “this event will likely be the most spatially extensive global bleaching event on record.”
Each of the three previous global money laundering events has been worse than the last. During the first, in 1998, 20 percent of the world's reef areas suffered heat stress to the level of bleaching. In 2010, it was 35 percent. The third spanned from 2014 to 2017 and affected 56 percent of the reefs.
The current event is expected to be shorter in duration, Dr. Manzello said, because El Niño, a natural weather pattern associated with warmer oceans, is weakening and meteorologists predict a colder La Niña period will occur toward the end. of year.
Money laundering has been confirmed in 54 countries, territories and local economies, as far away as Florida, Saudi Arabia and Fiji. The Great Barrier Reef in Australia is suffering what appears to be its most serious bleaching event; About one-third of the reefs surveyed by air showed a very high or extreme prevalence of bleaching, and at least three-quarters showed some bleaching.
“Sometimes I get depressed, because the feeling is like, 'Oh my God, this is happening,'” said Ove Hoegh-Guldberg, a professor of marine studies at the University of Queensland, who published the first predictions about how catastrophic global warming would be. . for coral reefs.
“Now we're at the point where we are in the disaster movie,” he said.
The most recent confirmation of widespread bleaching, which prompted Monday's announcement, came from the western Indian Ocean, including Tanzania, Kenya, Mauritius, Seychelles and off the western coast of Indonesia.
Swaleh Aboud, a coral reef scientist at CORDIO East Africa, a nonprofit research and conservation group based in Kenya and focused on the Indian Ocean, said coral species known to be heat-resistant are becoming bleaching, as do reefs in a colder area that are considered colder. be a climate refuge.
He recently visited a fishing community in Kenya called Kuruwitu that has been working to revive its reef. Many of the restored coral colonies had turned a ghostly white. Others were pale, apparently on their way.
“Urgent global action is needed to reduce future bleaching events, driven primarily by carbon emissions,” Aboud said.
Scientists are still learning about corals' ability to adapt to climate change. Efforts are underway to breed corals that tolerate higher temperatures. In a few places, including Australia and Japan, corals appear to be migrating poleward and beginning to occupy new locations. But scientists say a variety of factors, such as the amount of light penetrating the water and the topography of the seafloor, make that migration limited or unlikely in much of the world. There is also 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, authored a 2018 report from the Intergovernmental Panel on Climate Change that found the world would lose the vast majority of its coral reefs. at 1.5 degrees Celsius of warming, and practically all at 2 degrees. Current commitments by nations put the Earth on track for about 2.5 degrees by 2100. Still, hope has not been lost.
“I think we will solve the problem if we stand up and fight to solve it,” Dr. Hoegh-Guldberg said. “If we keep paying lip service but don't move forward with solutions, then we are fooling ourselves.”
