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"The magnitude and extent of the heat stress is shocking," said one marine scientist.
A year after scientists warned the world was seeing its fourth mass coral bleaching event, rising ocean temperatures fueled by greenhouse gas emissions have now devastated 84% of Earth's coral reefs—with likely knock-on effects for about a third of all marine species and 1 billion people whose lives and livelihoods are directly impacted by the health of the "rainforests of the sea."
Coral Reef Watch at the U.S. National Oceanic and Atmospheric Administration (NOAA) released its latest data on Wednesday, showing the current bleaching event has become the most widespread on record, impacting reefs from the Indian Ocean to the Atlantic and Pacific.
The news comes three months after scientists confirmed 2024 was the hottest year on record. Last year, meteorologists also found that sea surface temperatures in the North Atlantic were about 2°F higher than the 1990-2020 average and nearly 3°F above the average in the 1980s.
Unusually warm ocean waters cause corals to expel algae that give the reefs their bright color and deliver nutrients, supporting the immense biodiversity that is normally found within the reefs. Prolonged bleaching can kill coral reefs.
"The magnitude and extent of the heat stress is shocking," marine scientist Melanie McField, the founder of the Healthy Reefs for Healthy People initiative in the Caribbean, told Reuters. "Some reefs that had thus far escaped major heat stress and we thought to be somewhat resilient, succumbed to partial mortalities in 2024."
Derek Manzello, director of Coral Reef Watch, told The Guardian that some reefs that had been considered safe from the impact of rising ocean temperatures have now been bleached.
"Some reefs that had thus far escaped major heat stress and we thought to be somewhat resilient, succumbed to partial mortalities in 2024."
“The fact that so many reef areas have been impacted," he said, "suggests that ocean warming has reached a level where there is no longer any safe harbor from coral bleaching and its ramifications."
The current coral bleaching event began in January 2023. That same year, scientists were alarmed by an ocean heatwave off the coast of Florida that rapidly bleached the continental United States' only living barrier reef.
That event prompted NOAA to introduce a new coral bleaching alert scale from Level 1—significant bleaching—to Level 5, at which point a reef is approaching mortality.
Another ocean heatwave last year threatened Australia's Great Barrier Reef, eight years after nearly half of the coral in some northern parts of the 1,400-mile reef was killed by a mass bleaching event.
But recent major bleaching events affecting specific reefs have not compared to the current widespread devastation in the world's oceans. 
“Reefs have not encountered this before," said Britta Schaffelke, coordinator of the Global Coral Reef Monitoring Network, told The Guardian. "With the ongoing bleaching it's almost overwhelming the capacity of people to do the monitoring they need to do. The fact that this most recent, global-scale coral bleaching event is still ongoing takes the world's reefs into uncharted waters."
The other three mass bleaching events on record occurred from 2014-17, with 68% of the world's reefs affected; in 2010, when 37% were impacted; and in 1998, when 21% suffered bleaching.
The report from Coral Reef Watch followed the Trump administration's under-the-radar release of climate change data that minimized NOAA's findings about the level of planet-heating carbon dioxide emissions in the atmosphere. President Donald Trump also issued an executive order demanding sunset provisions for every existing energy regulation and notified companies that they can seek exemptions to clean air regulations.
Joerg Wiedenmann, a marine biologist at the Coral Reef Laboratory at the University of Southampton in England, emphasized that taking action to stop the heating of the world's oceans could protect coral reefs, the marine species they provide habitats to, and the communities they support by protecting coastlines and providing fishing and tourism jobs.
"If we manage to decrease ocean warming," Wiedenmann told The Washington Post, "there is always a chance for corals to recover."
"Higher temperatures in the U.K. are contributing to more severe heatwaves, droughts, and wildfires but also more intense rainfall events and associated flooding," said one climate scientist.
Last year was the hottest year on record in the United Kingdom, the national meteorological service reported Thursday, emphasizing that the human-caused climate emergency was what drove the country to see record-breaking heat last summer and an annual average temperature of 50°F, or 10.03°C.
Experts at the Met Office expect to see average yearly temperatures above 10°C as frequently as every three to four years as fossil fuel extraction and carbon emissions persist, while "in a natural climate" without human-induced planetary heating, such temperatures "would occur around once every 500 years," according to climate attribution scientist Nikos Christidis.
"It reinforces what scientists have been saying for decades now, that climate change is real and is happening."
Signs that the U.K. was experiencing an unusually hot year were evident last summer, when the country experienced temperatures above 104°F (40°C) for the first time ever.
"Human-caused climate change explains the unprecedented nature of the summer heatwave in the U.K. as well as the sustained warmth seen throughout most of 2022," Richard Allan, professor of climate science at the University of Reading, said in a statement. 
Christidis said the Met Office used "climate models to compare the likelihood of a U.K. mean temperature of 10°C in both the current climate and with historical human climate influences removed."
"Climate change made this around 160 times more likely," the Met Office said of the unusually high average temperature.
\u201cThe 2022 UK annual mean temperature was 10.03\u00b0C, the highest in records dating back to 1884. \n\nThis made the year 0.89\u00b0C above the 1991-2020 average and 0.15\u00b0C higher than the previous record of 9.88\u00b0C set in 2014.\n\n\ud83e\uddf52/4\u201d— Met Office (@Met Office) 1672908708
Stephan Harrison, professor of climate and environmental change at the University of Exeter, called the Met Office's report "extremely significant."
"It reinforces what scientists have been saying for decades now, that climate change is real and is happening, and it supports the arguments that change is likely to be faster over the land masses of the Northern Hemisphere than almost anywhere else," said Harrison. "The impacts of continued warming on agriculture and ecosystems will be profound."
The Met Office released its findings for 2022 as countries across Europe reported unusually warm winter weather, with ski resorts across the Alps shutting down during what's normally the height of skiing season. 
"Climate change is at work," Laurent Reynaud, managing director of Domaines Skiables de France, the national body representing ski resorts, told CNN Wednesday as he explained that about half of France's 7,500 ski slopes are closed due to "a lack of snow and a lot of rain."
Latvia, Lithuania, the Netherlands, and Poland are among the European countries that reported record warm temperatures on the first day of the new year this week.
Countries across the continent faced numerous extreme weather events last year that scientists said were made far more likely by fossil fuel emissions and their effects on the planet.
Extreme heat across Western Europe was blamed for more than 20,000 excess deaths, while heavy rains triggered a landslide that killed at least a dozen people on Italy's island of Ischia. 
"Higher temperatures in the U.K. are contributing to more severe heatwaves, droughts, and wildfires but also more intense rainfall events and associated flooding," said Allan, "and these impacts will become progressively worse until global temperatures are stabilized by cutting global carbon emissions to net zero."
Another month, another temperature record shattered.
NASA data released Monday shows that last month was the hottest August since record-keeping started in 1880 and tied with July for the warmest month in the previous 136 years.
According to NASA's Goddard Institute for Space Studies, August 2016's temperature was 0.16 degrees Celsius warmer than the previous warmest August in 2014. Last month, it was also 0.98 degrees Celsius warmer than the mean August temperature from 1951 to 1980.

Notably, NASA points out, "the seasonal temperature cycle typically peaks in July."
But recent months have been anything but typical. "The record warm August continued a streak of 11 consecutive months dating back to October 2015 that have set new monthly high-temperature records," NASA said in a press release.
What's more, climate scientist Stefan Rahmstorf pointed out on Twitter that the temperature has risen even though this year's unusually strong El Nino is on the wane.
\u201cNASA: hottest August on record. A bit of a shock - temperature has gone up again even though El Ni\u00f1o has subsided.\u201d— Stefan Rahmstorf \ud83c\udf0f fediscience.org/@rahmstorf \ud83e\udda3 (@Stefan Rahmstorf \ud83c\udf0f fediscience.org/@rahmstorf \ud83e\udda3) 1473705937
The National Oceanic and Atmospheric Administration (NOAA) will release its own August figures later this month.
Regardless, Mary Beth Griggs wrote for Popular Science, "this heat streak continues to put 2016 in the running to be be the hottest year since 2015, which broke the record set by 2014."
And while the endless string of "hottest months" may induce fatigue among some observers, Astrid Caldas of the Union of Concerned Scientists explains in a blog post on Monday why the string of broken records is still "big news."
"While there may be a tendency to be complacent about the recurring record temperatures, with each month come more climate-related consequences that cannot be ignored, and they make for big news stories," Caldas writes. "From wildfires and droughts to devastating floods, climate change fingerprint is all around us and does play a role in making events more extreme. An example are the recent Louisiana floods, caused by intense rains which, according to the science of attribution, were at least 40% more likely to happen because of climate change."
"Climate change is here, its effects are being already felt in a variety of ways...and we do not need to wait years or decades to see its effects," she says. "We should heed the warnings and act now, investing in preparedness and emissions reductions, so as to minimize possible added (and maybe worse) future risks and impacts."