It’s the worst news yet in a bleaching event that’s been going on for months now. A previous survey, conducted in September and October 2016, found that 56.7 percent of the reef had died, while 97 percent total had bleached. An even earlier survey, conducted in July and August, found that 89.6 percent of the reef had bleached, but only 5.4 percent had died.

The findings follow a summer marked by unusually high regional ocean temperatures, a primary cause of coral bleaching around the world. Between June and August 2016, water temperatures in the area hovered above 30 degrees Celsius, or 86 degrees Fahrenheit, said Mari Yamazaki, a member of the Environment Ministry’s Nature Conservation Bureau, in an email to The Washington Post. Japan’s Yomiuri Shimbun newspaper reports that average summer sea surface temperatures for the region are typically around 29 degrees Celsius. According to the Japan Meteorological Agency, sea surface temperatures around Japan have risen an average of 1.07 degrees Celsius in the past 100 years, which is more than twice the global average warming rate.

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Japan isn’t the only nation whose corals are suffering. A global bleaching event has been ravaging coral reefs all over the world for several years. Scientists believe a long-term pattern of rising ocean temperatures is largely to blame, although the damage was exacerbated in many places by the effects of an unusually severe El Niño event beginning in 2015.

Australia’s iconic Great Barrier Reef is among the most famous of the casualties. Just a few months ago, researchers announced devastating losses in the northern part of the reef, with up to two-thirds of the corals having died in some areas. And scientists have made similarly grim discoveries in many other reefs around the world, from the United States and the Caribbean to the Western Pacific.

Recent research suggests these bleachings are the culmination of a much longer-term pattern of ocean warming. A recent study conducted by scientists with the National Oceanic and Atmospheric Research Administration examined data on ocean warming trends and coral bleaching patterns around the world between 1985 and 2012 and found that 97 percent of the study sites showed warming trends, 60 percent of them significant. And the frequency with which these temperatures reached bleaching levels tripled during the study period.

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To be clear, bleaching doesn’t always spell death for corals — given time and the right conditions, they can recover. However, long-term warming patterns around the globe have many scientists worried that year after year of high temperatures, especially during the summers, means that corals won’t have adequate time to recuperate and will remain stressed into the future.

Another recent study suggests that under a business-as-usual climate change scenario, in which global greenhouse gas emissions remain high into the future, 99 percent of the world’s coral reefs will experience severe annual bleaching events by the end of the century. Even under a more moderate climate scenario, the study suggests about 75 percent of the world’s reefs will reach this point by 2070.

The study includes projections on a local level as well. Under a business-as-usual scenario, it suggests that coral reefs around Japan will begin to experience annual severe bleaching by 2047.

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For the time being, the future of Japan’s largest reef remains uncertain. “We do not know when the reef will recover,” Yamazaki noted by email. According to the Environment Ministry, the survey findings will be presented at a “nature rehabilitation” council in February.

The reef has experienced several severe bleaching events in the past, said Yamazaki, including in 1998 — another severe El Niño year — and 2007. And according to reports from the Environment Ministry, a committee was established in 2007 to work on restoring the region’s coral reef ecosystem. Some of its priorities included removing aggressive crown-of-thorns starfish, which feed on coral, from the area, and cutting down on water pollution from agricultural activities.