The report places the critical temperature threshold at around 1,2 degrees of global warming compared to the pre-industrial era, a level the planet has already left behind. Even if the temperature were to stabilize at 1,5 °C, the document predicts that more than 90% of the reefs will suffer severe degradation, with consequences for biodiversity, fisheries and natural coastal protection.
A climate threshold already crossed
From 2016, successive marine heat waves have triggered large-scale bleaching events that have affected most tropical reefs. In 2022, the Great Barrier Reef recorded a massive event. despite an episode of La Niña, a phase that normally brings rain and somewhat cooler waters to the region.
The figures are overwhelming: the fourth global episode of bleaching, which began in 2023, has already damaged more than 80% of the reefs, with recent estimates putting the impact above 84%Furthermore, the recovery periods that used to separate one event from the next have virtually disappeared, reducing the system's resilience.
Experts point out that the dynamics have accelerated. Researchers in marine ecology emphasize that the recovery interval between disturbances is almost non-existent, a situation that places corals at the limits of their thermal and functional tolerance.
What it means for reefs and for people
Tropical reefs support fisheries, tourism and coastal defense, and are home to an enormous diversity of species. It is estimated that their good condition directly or indirectly impacts the well-being of hundreds of millions of people, especially in low-lying coastal communities.
Among the most immediate effects are: lower food security due to the decline in fishing populations, a decrease in income linked to marine tourism, and an increased risk of storms and coastal erosion due to the disappearance of the natural barrier provided by the reef.
Even if warming is limited to 1,5°C, the probability of reefs crossing or remaining beyond their thermal threshold is practically safe (around 99%), according to the assessment. The margin for maneuver is already so narrow that large-scale recovery would not be feasible without a sustained cooling of the waters.
In fact, the analysis suggests that to conserve reefs on a large scale, the global average temperature would need to return to around 1 °C above or below pre-industrial levels. In the short term, efforts should focus on protect thermal shelters and improve habitat quality to maintain ecological functions where it is still possible.
Risk chain in the terrestrial system
The report is not limited to corals: it identifies 26 possible turning points in the Earth system and emphasizes that its connections are mostly destabilizing. The Atlantic Meridional Overturning Circulation (AMOC) appears as a central axis in many of these interactions.
Among the systems under pressure are: weakening of the AMOC, with the potential to alter the climate of the North Atlantic; the loss of ice mass in Greenland and West Antarctica, with long-term impacts on sea level; Arctic permafrost, which already emits methane and COâ‚‚ due to abrupt melting; Amazon, whose resilience is diminished by deforestation, fires and global warming; and the boreal forests, exposed to fires, pests and droughts capable of releasing large reserves of carbon.
Climate experts stress that the scope and magnitude of the impacts increase each year, and that more population experiences long-lasting effects and various warming factors. This acceleration increases the risk of abrupt transitions and reduces the time available for effective adaptation.
What can be done now
The diagnosis is clear: it is urgent to drastically reduce the Emissions of greenhouse gases and accelerate the energy transition. The report also identifies positive signs, such as the rapid expansion of solar energy, electric vehicles, batteries and heat pumps, which are beginning to displace carbon-intensive technologies.
To buy time for corals, priorities include protecting sturdy shelters, reduce local pressures (overfishing, pollution, wastewater discharges) and strengthen the management of marine protected areas. On a global scale, the authors suggest that it may be necessary to active COâ‚‚ extraction from the atmosphere, along with mitigation, to regain a safe thermal margin.
With the upcoming United Nations climate summit in Belém (COP30) On the horizon, the scientific community is calling for an unprecedented mobilization of policies and resources to prevent other vital systems from crossing their own thresholds, with particular attention to the cascading risks between elements of the Earth system.
The message left by this assessment is that we are already living with a new climate realityCoral reefs have crossed their tipping point, and other systems are approaching theirs. The scope for action lies in rapidly reducing emissions, protecting what remains, and deploying solutions that reduce temperatures and, where possible, restore ocean balance.