Warm-water coral reefs have crossed a tipping point due to global heating and are dying at an accelerated rate due to repeated mass bleaching events, impacting hundreds of millions of people who rely on them for fishing, tourism and protection from rising seas and storm surges, according to new research.
Global average temperatures are about 1.3-1.4C above pre-industrial times, which is higher than coral reefs can withstand. Their thermal tipping point is estimated to be 1.2C of warming.
If the trend is not reversed, coral reefs around the world will be lost, warned the second Global Tipping Points report, released on Monday and produced by more than 160 scientists in 23 countries, led by the Global Systems Institute at the UK’s University of Exeter.
Of the seven tipping points monitored by the researchers, this is the first to be shown as already passed. “We’ve actually already lost about half our warm-water coral reef cover, and we can expect accelerated change in the next few decades as well,” said Mike Barrett, chief scientific advisor at WWF-UK.
The report also said parts of the West Antarctic and Greenland ice sheets are losing ice at an accelerating speed, coming close to collapse. Greenland’s ice sheet is losing 266 billion tonnes of ice mass per year. If that meltwater flows into the North Atlantic and destabilises its subpolar gyre (large rotating current), it could produce a “Little Ice Age” in Europe, with worsening heatwaves in the summer but freezing months in the winter.
The report also said the Amazon rainforest is at greater risk than previously thought. Steven Smith from the Global Systems Institute told a webinar on the report that “the combined effects of climate change and deforestation put this [the rainforest] under threat between 1.5 to 2 degrees of warming.”
Overshooting the 1.5C warming limit governments promised to try to keep to under the Paris Agreement now looks “pretty inevitable”, and could happen around 2030, according to the report.
The researchers said they are working with Brazil to ensure that tipping points are discussed at the COP30 climate summit it will host in November, highlighting actions that need to be taken fast.
Those include phasing out fossil fuels, increasing support for clean technologies and infrastructure, and switching to more sustainable food systems.
“Governance systems, national policies, rules, multinational agreements – including the Paris Agreement – were not designed with tipping points in mind,” said Manjana Milkoreit from the University of Oslo. “They’re made for linear or gradual changes, not the abrupt, irreversible and interconnected shifts in the Earth systems that we’re now facing.”
The consequences of a warming ocean
Corals not only provide livelihoods, food security and protection from tropical storms for over half a billion people – they also deliver $2.7 trillion annually in global economic benefits, the scientists said.
Melanie McField, founder and director of the Healthy Reefs for Healthy People Initiative (HRI), explained that the tipping point is not necessarily irreversible, as not all corals are affected at the same time – and ocean protection efforts in general could save them from becoming victims of overfishing and pollution.
In recent weeks, new reports have confirmed the effects of heat on the oceans and marine life. The EU Copernicus Ocean State Report showed that almost a quarter of the global ocean surface experienced at least one severe to extreme marine heatwave event in 2023 – a trend that has accelerated since 2005.
And last month, the annual planetary boundaries report from the Potsdam Institute for Climate Impact Research (PIK) said the planetary limit for ocean acidification had been surpassed for the first time, weakening the oceans’ ability to act as Earth’s stabiliser.
Oceans turn more acidic by absorbing CO2 from the atmosphere, a process that threatens marine life, with 1,677 species at risk of extinction, PIK said. The Copernicus report indicates a 16.5% increase in ocean acidity since 1985.
Meanwhile, ocean heatwaves not only have become more frequent but have also caused the planet’s seas to reach new record temperatures. The warmest the ocean has been since satellite data started to be collected was in spring 2024, when the global average hit 21C. More than 90% of the excess heat trapped in the Earth’s system due to human-caused global warming has been absorbed by the oceans, according to the US National Oceanic and Atmospheric Administration.
Marta Marcos, an associate professor at the University of the Balearic Islands and one of the Copernicus’ study authors, told Climate Home News another key issue is the acceleration in sea level rise, which began speeding up in the 1960s-70s and is now above 4 millimetres per year. “Sea level not only continues to rise, but is rising at an ever faster rate,” she said.
While sea level rise is a global trend, the major risk is in densely populated cities near the sea. For example, in Europe around 200 million people live near coastlines – and higher baseline sea levels increase the threat to their homes and infrastructure from extreme weather. “When a storm comes, with its surge and waves, it has a much greater destructive potential,” explained Marcos.
Blue NDCs bring oceans into climate plans
Marcos believes there is growing government interest in protecting the oceans. In September, the High Seas Treaty, which lays the ground for the creation of marine protected areas (MPAs) in international waters, reached the 60 government ratifications needed for it to take effect.
And during New York Climate Week in September, Chile and the UK committed to include ocean-based solutions in their national climate plans (known as NDCs). Eleven countries have now joined the “Blue NDC” project which encourages governments – depending on their circumstances – to manage marine ecosystems, phase out offshore oil and gas production, expand clean ocean energy, cut emissions and support sustainable fisheries.
Others with Blue NDCs are Brazil, France, Australia, Fiji, Kenya, Mexico, Palau, Madagascar and the Republic of Seychelles.
Such ocean-based solutions can provide 35% of the emissions reductions the world needs by 2035, a study by the High Level Panel for a Sustainable Ocean Economy shows.
Mary Creagh, the UK’s minister for nature, said oceans are central to her country’s NDC – but work is still being finalised on how to count emissions reductions from seagrass and seaweed management and coastal restoration. “We’re working on the science, which we’re happy to share globally once it is complete,” she added.
One key challenge is getting the world’s largest fish-producing countries to sign up to tackle ocean issues in their climate plans, particularly Asian heavyweights such as China, Indonesia, India and Vietnam.
Blue NDC member and COP30 host Brazil, meanwhile, recently announced its largest oil and gas discovery in 25 years in the Santos Basin, 400 kilometres off its coast.
Nonetheless, Marcos said such initiatives are important, adding that any effective action “has to be global, coordinated, and based on data and science”.
Marinez Scherer, a marine biologist and coastal management expert who is the COP30 Special Envoy for Oceans, said the upcoming operationalisation of the High Seas Treaty is a step forward on the path to the climate summit, which she said would discuss a plan to speed up implementation of ocean solutions.
Scherer said COP30 will present measures that are currently working in Brazil and show the world what’s needed to “plan and manage the ocean in a very healthy and sustainable way”.
