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The Earth has reached its first catastrophic tipping point, with widespread bleaching and death of coral reefs. Surging global temperatures have pushed these sensitive yet vital ecosystems towards irreversible decline, warns the “Global Tipping Points Report 2025”. Prepared by 160 scientists from 23 countries, the report states that warm-water coral reefs, or shallow coral reefs in tropical and sub-tropical regions, are crossing their thermal tipping point and undergoing unprecedented die-off. This collapse threatens the livelihoods of nearly one billion people who depend on reefs for food, income and coastal protection. The report was released ahead of the 30th UN climate summit (COP30), where countries are expected to set out their goals for bringing down emissions over the next decade.
The report also warns that the world is “on the brink” of reaching other tipping points, including the dieback of the Amazon rainforests and Eurasian boreal forests, collapse of major ocean currents such as the Atlantic Meridional Overturning Circulation (AMOC) and the sub-polar gyre (SPG) and melting of ice sheets, including land permafrost and mountain glaciers (see ‘Escalated risks’, p38). “We’re in a new climate reality,” says Tim Lenton, founding director at Global Systems Institute at the University of Exeter, UK, who led the report. “We have crossed a tipping point in the climate system, and we’re now sure we’re going to carry on through 1.5°C of global warming above the prior industrial level, and that’s going to put us in the danger zone for crossing more climate tipping points.”
According to the Intergovernmental Panel on Climate Change (IPCC), tipping points are “critical thresholds” that, when exceeded, can lead to significant changes in the state of the system. This change, which is often irreversible, is propelled by self-perpetuating feedback loops, even if what was driving the change in the system stops.
It is no surprise that of all the tipping points, coral reefs are the first to be breached. Warm-water coral reefs are highly sensitive and complex ecosystems built around the symbiotic relationship of reef-building corals and photosynthetic algae, zooxanthellae. These microscopic algae live in the tissues of corals and provide them with nutrients, oxygen and vibrant colours.
Together, they form the world’s most diverse marine ecosystems, filled with colourful fish and invertebrates that are found nowhere else on earth. When stressed by rising ocean temperatures, corals expel these algae. And the underwater riot of colour and life is replaced with a bleached landscape where corals become more susceptible to disease and death.
While natural bleaching events do occur, after which most corals recover, scientists are worried by the increasing frequency and intensity of marine heatwaves, which prevent recovery between heatwaves, triggering mortality. The current global bleaching event is the fourth such event, ongoing since January 2023. It is the most severe on record and has so far, affected nearly 85 per cent of coral reefs across over 80 countries. It is also the second such event in less than a decade. The first major episode occurred in 1997 and 1998, when 16 per cent of the world’s reefs were destroyed across 60 countries and island nations. The subsequent mass bleaching events occurred in 2010 and in 2014-17. “We have now pushed [coral reefs] beyond what they can cope with,” says Mike Barrett, chief scientific advisor at the World Wildlife Fund UK and co-author of “Global Tipping Points Report 2025”.
The impact is severe in the Caribbean and wider regions, where global ocean circulation changes are heightening and prolonging heat stress episodes, notes the report. It highlights that bleaching events in this region are occurring quasi-annually and becoming desynchronised from El Niño events (part of the natural El Niño-Southern Oscillation or ENSO cycle, characterised by a warming of the eastern and central tropical Pacific Ocean). Bleaching in normal and even La Niña years (characterised by cooling of the ENSO cycle) is now common.
In the Great Barrier Reef (GBR) region of Australia, the ocean reached unprecedented warming levels, duration and depth, leading to rapid bleaching, disease onset, and mortality in diverse corals, including genera that were considered resilient. Some areas have lost over 70 per cent hard coral cover. Catastrophic bleaching has occurred in protected reefs of the southern GBR and Coral Sea. A reef to rubble phenomenon is occurring, whereby colonies fragment and transition to rubble as part of a transformation towards lower complexity ecosystems that are difficult to recover from. Lizard Island, where cumulative heat stress exposure has been lower than many other parts of the GBR, has also recorded one of the highest rates of bleaching mortality.
As in the Caribbean, bleaching on the GBR is now becoming a biennial event. Scientists who have authored the report conclude that the GBR ecosystem is under existential threat owing to highest temperature in 400 years and, is at increasing risk of regime shifts from coral dominated systems towards non-coral dominated landscape.
While ocean heating has become the dominant global-scale threat to coral reefs, what is adding to the problem are stressors such as unsustainable fishing, water pollution, disease, nutrient enrichment and predator imbalance, states the report. Over 80 per cent of the world’s coral reefs are severely overfished or have degraded habitats. Studies show that microplastics are also reducing the productivity of corals, thereby contributing to their decline.
“The evidence of the fourth global bleaching event that currently is still progressing is worrying,” David Obura, chair of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), tells Down To Earth (DTE). A marine biologist by training, Obura has spent over 30 years studying coral reefs and is the founding director of Coastal Oceans Research and Development in the Indian Ocean (CORDIO) East Africa, which began as a response to the mass coral bleaching event of 1988. Obura says that unlike other tipping systems, coral reef collapse will unlikely lead to human deaths by itself, but it will cause major social disruptions and hardships, as well as cascading impacts to other ecosystems as dependence is shifted to these.
For instance, Obura explains, coral reefs provide habitat to many species (one-quarter to one-third of marine species by some estimates). For communities living in areas near coral reefs, they provide food, coastal protection, medicines, recreation and much more. Even a degree of coral species extinctions will lead to a collapse in many food webs and interaction webs that depend on the complexity of coral reef ecosystems. This means declining biodiversity and productivity of locations where coral reefs are found. This will be catastrophic to small dependent communities, leading to increasing poverty.
“Unless we return to global mean surface temperatures of 1.2°C (and eventually to at least 1°C) as fast as possible, we will not retain warm-water reefs on our planet at any meaningful scale,” the report states.
The group’s first such assessment, released in 2023, raised alarms but did not officially declare that any climate tipping points had been reached. In the past few years, however, global temperatures have surged, sparking concerns among some scientists that global warming is accelerating and could lead to even more widespread impacts in the coming decades than the changes that have already been recorded. The impact on coral reefs has also been particularly severe in the past two years, pushing them to their tipping point.
Corals would continue to decline even if humans stabilise global temperatures at around 1.5°C above pre-industrial levels, a goal under the 2015 Paris climate agreement. But the 1.5°C threshold could be breached within the next several years, researchers say. As Steve Smith, a social scientist at the University of Exeter, UK, and a lead author of the report, puts it: “We can no longer talk about tipping points as a future risk.”
This article was originally published in the cover story Fading reefs in the November 1-15, 2025 print edition of Down To Earth