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The world lost about 14 percent of its coral reefs in the decade after 2009, mainly due to climate change. comprehensive international report about the state of corals in the world.

While the decline highlights the disastrous consequences of global warming, it also offers hope that some coral reefs can be saved if people act quickly to rein in greenhouse gases.

“Coral reefs tell us how quickly canaries in the coal mine can go wrong,” said David Obura, one of the report’s editors and head of the International Union for Conservation of Nature’s coral expert group.

He said the 14 percent drop was cause for deep concern. “In finance, we are concerned about half-percent reductions and half-percent changes in employment and interest rates.”

The report’s editors said it was the trend that was particularly worrying. The first global bleaching event occurred in 1998, but many reefs have returned. This is no longer the case.

“There has been a steady decline at the global level since 2009,” said Serge Planes, a research scientist at the Center for Island Studies and Environmental Observatory in Moorea, French Polynesia, who also edited the report.

While coral reefs cover a very small part of the ocean floor, they provide enormous benefits to humans. Its fish provide a critical source of protein to one billion people. Limestone branches protect the coast from storms. Their beauty supports billions of dollars in tourism. Collectively, they support an estimated $2.7 trillion a year in goods and services, according to the report released by the International Coral Reef Initiative, a partnership of countries and organizations working to protect the world’s coral reefs.

There are perhaps 900 coral species, and some of them appear to be more resilient to the heat and acidification that accompanies climate change, the researchers noted. Unfortunately, these are not the more familiar, reef-forming varieties that grow slower and support the richest biodiversity.

Terry Hughes, who runs a center for coral reef studies at James Cook University in Australia, who was not involved in the analysis, also warned that the broad underlying data collected by more than 300 scientists in 73 countries could lean towards healthier reefs. .

Dr. “Researchers and monitoring programs often leave degraded sites or don’t do new work there because no one wants to study a reef covered with silt and algae instead of corals,” Hughes said.

Still, both he and the report stressed that corals can recover or regenerate if the world limits global warming. “Most of the world’s coral reefs remain resilient and can recover if conditions allow,” the report said.

While the scientists said that tackling climate change is the most important factor in protecting coral reefs, reducing pollution is also critical, he said. Corals need to be as healthy as possible to survive the warming temperatures that are already locked in. Harmful pollution often includes human sewage and agricultural runoff, which can cause algal blooms, as well as heavy metals or other chemicals from manufacturing. Destructive fishing practices also damage reefs.

The report comes just before world leaders meet next week to discuss a new global agreement on biodiversity. While some strive to preserve the most pristine reefs, Dr. Obura said that this approach will not be enough.

Dr. “People are so dependent on reefs around the world that we have to put a lot of effort into mediocre reefs or all other reefs,” Obura said. “We need to keep people working so that their livelihoods can continue.”