May 25, 2024

About a year ago, the sea became unusually warm, even by our current, overheated standards. Twelve months of broken records later, the oceans even more feverish than can explain climate models and normal fluctuations in global weather patterns.

When the ocean turns into bathwater, it threatens the survival of the planet’s coral reefs, home to a quarter of all marine life and a source of food for many people living along the world’s coasts. Coral reefs are mostly clustered in the shallow waters of the tropics, and have one of the lowest thresholds for rising temperatures of all the possible “vertical points,” the cascading feedback loops that caused large, abrupt changes in the ecosystems, weather patterns and ice formations on Earth. Stable, existing systems end up in new, completely different conditions: The lush Amazon rainforest, for example, can crash into a grassy savannah. Coral reefs can turn into seaweed-choked graveyards.

Earlier this month, the world officially entered its fourth — and arguably worst — one mass coral bleaching event in history, according to the National Oceanic and Atmospheric Administration and the International Coral Reef Initiative. Warm water causes corals to expel the tiny algae that live in their tissues, which provide them with food (through photosynthesis) and also a rainbow of pigments. Separated from their algae, corals “bleach”, turn ghostly white and begin to starve.

The Florida Keys, where water temperatures veered toward hot tub territory last year, saw it most severe bleaching event to date, with scientists”evacuate thousands of corals to tanks on land. In Australia, the iconic Great Barrier Reef is also faced his biggest test yet. In the Indian Ocean, even coral species known to be resistant to hot temperatures is bleaching.

“This is one of the major living systems that we thought was closest to a tipping point,” said Tim Lenton, a professor of climate change and Earth systems at the University of Exeter in the United Kingdom. “It’s kind of horrible confirmation that it is.”

an estimated 1 billion people around the world benefit from coral reefs, which provide food and income, while also protecting coastal property from storms and flooding. The benefits amount to approx $11 trillion a year. With some scientists concerned that coral reefs may have already passed a point of no returnresearchers are resorting to desperate measures to save them, from building artificial reefs to efforts to cool reefs through geoengineering.

Last year, the warmer weather pattern known as El Niño gripped the globe, global average temperatures temporarily up to 1.5 degrees Celsius (2.7 degrees Fahrenheit) of warming over pre-industrial times. This is exactly the level scientists predicted it would be between 70 and 99 percent of tropical reefs would disappear. With a cooler La Niña phase on the way this summer, it’s possible that corals will make it through the current onslaught of warm ocean temperatures. But every week high temperatures continue, another 1 percent of corals are predicted to bleach. By the early 2030s, global temperatures on the way to pass the 1.5 C threshold for good, compared to about 1.2 C today.

Tourists snorkel in the Great Barrier Reef in early April, swimming above bleached and dead coral. David Gray/AFP via Getty Images

Bleaching does not mean certain death, but the corals that survive have difficulty reproducing and are more susceptible to disease. Even when reefs recover, there is usually a loss of species, said Didier Zoccola, a scientist in Monaco who has studied corals for decades. “You have winners and losers, and the losers, you don’t know if they’re important in the ecosystem,” he said.

For a coral reef, the tipping point would come when bleaching becomes an annual event, according to David Kline, the executive director of the Pacific Blue Foundation, a nonprofit organization working to preserve reefs in Fiji. Species would die out, leaving only the most heat-tolerant creatures, the “cockroaches” of corals that can survive harsh conditions. Seaweed would begin to take over. Parts of the world may be approaching this point, if it has not already passed: The Great Barrier Reef, for example, has passed five mass bleaching events in the last eight years, leaving little chance for recovery. Florida has already more than lost 90 percent of its coral reefs.

“I think most scientists, myself included, would be very uncomfortable saying we’ve reached a tipping point,” said Deborah Brosnan, a longtime coral scientist who founded the reef restoration project OceanShot. “But in reality, are we very close to a tipping point? I believe we are, judging only by the extent of the bleaching we see.”

Rows around the world already have halved since the 1950s due to climate change, overfishing and pollution. Some scientists argue that the world may have long passed the point of no return for corals, as far back as the 1980s, but there is no consensus. “If we really want to have healthy, diverse coral reefs in the future, we need to do something about our greenhouse gas emissions, like we do now,” Kline said.

Rising temperatures may have already caused other notable tipping points, such as the accelerated melting of the Greenland ice and the thawing of the northern permafrost, which threatens to release large quantities methane, a powerful greenhouse gas. Coral tipping points will unfold regionally, with giant blobs of warm ocean water destroying reefs, which Lenton calls a “grouped” tipping point.

Coral reefs are so vulnerable, in part because their existence is fragile in the first palace. Ridges are “a green explosion of life in a nutrient desert,” Lenton said, that can only exist because of “really strong reinforcing feedback loops within the system.” An intricate web of corals, algae, sponges and microbes move essential nutrients such as nitrogen around, leading to an abundance of life. “Not surprisingly, if you push it too hard, or turn certain things off, you can drop it into another ‘no coral’ state, or maybe several different states.”

Losing corals can lead to consequences you wouldn’t expect. For example, you can thank corals for the sand on many beaches – they help create it (coral skeletons turn to sand) and protect beaches from erosion, with the structure of the reef calming waves before they reach the shore. Rows contribute to medical breakthroughs – organisms found in it produce compounds used to treat cardiovascular disease and some types of cancer.

Researchers are racing to save what’s left of corals and the ecosystems they support. A restoration project in the Caribbean that Brosnan founded, called OceanShot, is build artificial reefs where natural collapsed. The layered structures provide habitat for reef-dwelling creatures, both the larger species that live on top and the smaller ones that like to hide in crevices lower down. The installations have had good results, with dozens of fish species moving in along with invertebrates such as crayfish. Even fine black urchins transplanted onto the reef decided to stay. Brosnan’s team also hopes to deploy them in places where beaches are being lost, as the artificial reefs could also help prevent sand from washing away.

Some conservation efforts are pretty out there. Scientists with the Smithsonian’s National Zoo and Conservation Biology Institute in Washington, DC, for example, is busy freezing coral sperm and larvae through “cryopreservation,” Futurama-style, with the hope that they can repopulate oceans of the future. In the Great Barrier Reef, researchers experimented with clouds brighten with sea salta form of geoengineering, to try and protect corals from the hot sun.

Elsewhere, labs are breeding corals to withstand heat and ocean acidification. Zoccola is working on one such project in Monaco, where scientists use “assisted evolution” to speed up nature’s process, as corals cannot adapt quickly enough in nature. He calls it a “Noah’s Ark” for corals, with the hope that species can live in the lab until one day they are ready to return to the ocean.

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