Are we heading for cascading tipping points?

A new review study examines four of the most dangerous climate tipping elements, confirming that they are destabilising. Risks are increasing that they will flip and not just in isolation.

Scientists and the public are becoming increasingly concerned that several parts of the Earth system may abruptly flip to alternative stable states with disastrous consequences for both the biosphere and humanity. Human caused climate change and land use practices are driving these critical systems towards their tipping points.

The paper¹ reviews four such interconnected systems, the Greenland ice sheet (GrIS), the Atlantic Meridional Overturning Circulation (AMOC), the Amazon rainforest and the South American Monsoon system (SAM). It presents observation-based evidence that the stability of these four tipping elements has declined in recent decades, suggesting that they have moved towards their critical thresholds, which may be crossed in the near future through unmitigated global warming. The results show a need for better monitoring of these tipping elements and for increased efforts to stop greenhouse gas emissions and land-use change.

What is a tipping element?

Put simply, a tipping element is a system that has more than one stable state and that what controls which state it resides in is determined by some outside force or effect. Imagine a chair rocking on its back legs. It has two stable states which are standing upright on four legs and laying on its back. When it is on all four legs, it can be rocked backwards slightly and it will return to the stable state, perhaps overshooting a bit before settling back to a static position. If it is pushed back quite a lot, it will still return to upright, but if we push it just a tiny bit more, it will pass a balance threshold and rather than return to upright, it will accelerate to the fallen-over state. Once there it is again stable, pushing it up a bit will return it to the same fallen position. You have to push it all the way past the balance threshold again to get it to move back to the upright state. The balance point is the tipping point of the system.

Tipping element behaviour. On the left a simple chair, on the right the mathematical analysis from the paper.

Two observations can be made for the behaviour of the chair as it gets further away from its stable upright position. Imagine that we increase the pushing force in equal steps before letting go and let’s say that 10 units of force are required to knock the chair beyond its balance threshold so that it falls over. The first step, 1 push unit out of 10, results in the chair rocking a small amount and very quickly returning to upright. 2 push units results in it going back further, but interestingly it goes back slightly more than twice the amount of the first step, and returns slightly slower than twice the time of the first step recovery. This trend continues all the way to the last step. At 9 out of 10, it still returns but much more slowly and with a few overshoot corrections, taking much longer to settle.

Mathematically, these two observations are called variance and lag-one autocorrection (AC1) and combine to create the indication of Critical Slowing Down (CSD). The recovery time from a small variation gets longer, the variation rate slows down as the tipping point approaches. Looking at the variance and CSD of a system over time can then be used as an Early Warning Signal (EWS) that the system is approaching a tipping point. This approach is used to determine observational measurements that can detect CSD so providing warning signals of increasing instability and the approach of tipping points.

The paper goes into the mathematics for those so inclined (no pun intended).

Observational evidence for destabilisation of the four coupled tipping elements

Understanding of the underlying physical processes and systems allows the identification of feedbacks that, associated with their CSD measurements, leads to an expectation that EWS are expected to precede abrupt changes of all four of the tipping elements studied. This is backed up by paleoclimate evidence of changes in the past and in model simulations. For each one, recent observation-based results show they have been destabilising over recent decades.

The physical world is a lot more complex than a chair or simple theoretical model. This creates uncertainty and the risk of both overestimating and underestimating stability, even though the implications are huge. A precautionary principle should suggest we err on the side of caution, but our socioeconomic system is not wired that way.

Figure from the paper showing the behaviour and variation increases of the four tipping elements.

Greenland Ice Sheet

There are two main feedbacks that drive the potential of a critical transition. There is an ice-albedo feedback where melted snow layers expose darker ice that absorbs more sunlight and warms faster, driving further melting. There is also a melt-elevation feedback where melting reduces the surface height of the ice sheet, exposing it to higher temperatures at lower elevations, leading to further melting. These are both termed self-amplifying or self-reinforcing feedbacks.

These feedbacks suggest a critical surface temperature threshold beyond which stability is lost and the ice sheet collapses to a new stable (melted) state. The system is complicated however due to the high inertia. It will take hundreds to thousands of years to reach the full melted state, so temporary exceedance of the threshold could avoid a tipping. Given the extended periods of time required to observe changes, detection could be after the point is crossed.

Data from shallow ice cores confirm that melting has accelerated substantially in recent decades coupled with increasing variance and AC1. Model analysis shows that the data fits the scenario of the GrIS approaching its tipping point.

Attributing the detected CSD to the different feedbacks and to the whole complexity of the ice sheet dynamics is more problematic. Precipitation over the area is expected to increase with a warming climate which could preserve ice mass balance, but only if it falls as snow rather than rain. This also affects the albedo feedback. Isostatic rebound is also a consideration. As the weight of ice reduces, the land rises. The difference between these rates will affect the melt-elevation feedback. There may even by other stable ice sheet volumes at different temperatures between a full pre-industrial level and a full melt. Sea ice concentration and glacial termination and melt characteristics are also variables that need to be considered.

Atlantic Meridional Overturning Circulation

For the AMOC, the factor that leads to the bistability and hence tipping point is the salt-advection feedback. Paleoclimate evidence confirms that the AMOC has relatively abruptly switched between an on and off state many times before, though only during glaciated periods. Climate models also show the potential for future changes, although some have difficulty due to poor ice melt coupling and low climate sensitivity. When extended beyond 2100 however, most show abrupt collapse. Given the inherent lack of sensitivity in these models, many scientists now feel the tipping point is likely to be reached this century.

The AMOC is driven by the sinking of dense salty water in the North Atlantic, creating the bottom water which flows south as part of the wider ocean circulation system. The AMOC draws in warm salty water from the south which is responsible for the temperate climate of north western Europe.

The increase in GrIS melt, reduction in sea ice, and increases in rain run-off from northern continents is freshening the north Atlantic as temperatures rise, making dense water formation more difficult. Direct observations of AMOC strength indicate a decline, but data has only been available for a few decades. Other studies using fingerprints of AMOC slowdown go back further and are verified by climate models. Recent work has confirmed the existence of EWS which tally with paleoclimate data.

These results suggest that, over the past century, the AMOC has evolved from relatively stable conditions towards a state that is nearing a critical transition. Another paper published last week² used clam shell growth rings from all over the North Atlantic basin to assess changes in the sub-polar gyre, a key part of the AMOC system. They detected a known shift in behaviour in the 1920s but also a second and stronger destabilisation beginning around 1950 that continues to today, supporting evidence of recent destabilisation as the system heads towards a tipping point.

Researchers have attempted to use these EWS to predict a time of collapse of the AMOC, but the uncertainties inherent in such a prediction are too large for it to yield reliable estimates of potential tipping times.

The implications of AMOC tipping are so huge that even if there is a 5% chance of it happening this century, that’s too great a risk to take. If it’s a 50% chance, as many experts believe, this needs to be taken extremely seriously.

Amazon Rainforest

The Amazon rainforest is threatened by a combination of changing precipitation regimes and drought patterns due to climate change on the one hand and deforestation to make space for cropland and pasture on the other.

The principle stable states are rainforest and savanna. A determining factor for Amazon rainforest resilience, and suitable variable to look at CSD is the amount of rainfall and its distribution over the year. Only rainforest-type vegetation is stable under very high mean annual precipitation (MAP), whereas savannah-type vegetation dominates for low MAP conditions.

The MAP is linked to overall global mean temperature regimes and hence global warming, but also to deforestation and degradation which reduces the forests ability to move water through transpiration, disconnecting the whole forest from the ocean and to areas of rainfall. It has been estimated that the temperature tipping point of the Amazon is between 3-5ºC without deforestation, but this drops to 1.5-2ºC with 20-25% deforestation. Both these points are being approached.

CSD and EWS can be detected through the response of the forest to droughts and wildfires. Recent results that are based on different remotely sensed vegetation indices have shown a widespread loss of resilience since the early 2000s, with faster resilience loss in regions with a lower MAP and in areas closer to human land-use activity.

If Amazon rainfall patterns change in response to tropical Atlantic sea temperature variations, for example, from AMOC weakening, and cross a threshold in MAP or dry-season length, the rainforest could flip and transition to a savannah environment. Once in that state, re-establishing forest cover would be extremely difficult.

South American Monsoon

Deforestation and degradation of the Amazon rainforest pose arguably the greatest threat to the ecosystem with serious knock-on effects to the south. Transitions from rainforest to savannah reduce the moisture that is fed back across the Amazon basin and beyond.

This recycled moisture is key to a positive feedback between convective latent heating over the Amazon and the low-level inflow of moist air from the tropical Atlantic Ocean. A deforestation-induced breakdown of this feedback could lead to a state shift of the South American monsoonal circulation and hence to abrupt and substantial rainfall reductions in the western Amazon and further downstream towards subtropical South America.

Time series analysis of monthly rainfall rates indicate CSD of this system. These EWS are consistent with approaching the breakdown of the feedback between latent heating and moisture inflow to the Amazon basin. Moreover, a collapse of this positive feedback should be preceded by an increasing dry-season length, which has been reported for large parts of the Amazon.

Not only is the Amazon approaching its tipping point, the coupled SAM is also approaching its coincidental collapse.

Cascading tipping elements

The four systems described are strongly coupled. GrIS melting is linked to AMOC weakening, Amazon die-off is linked strongly to the SAM collapse. They are also coupled to a larger network of tipping elements and feedbacks which makes modelling, prediction and selection of EWS highly complex.

The linkage between AMOC and the Amazon is less clear. A weakened or collapsed AMOC would reorganise precipitation patterns across tropical South America by reshaping the ocean temperatures in the tropical Atlantic and by driving a southward shift of the Intertropical Convergence Zone. Both observations and model simulations indicate that the relationship between sea surface temperature anomalies in the northern and southern tropical Atlantic plays a key role in rainfall anomalies in the Amazon. In addition, AMOC weakening leaves excess heat in the tropical South Atlantic which strengthens the Pacific trade winds and intensifies the Walker circulation, a key control on precipitation in tropical South America.

Even the link between the GrIS and AMOC is hard to model since although initial melting will reduce the AMOC strength and could tip it, once weakened, less heat would be transported to the area by the ocean currents which could increase seasonal sea ice, slow ocean terminating glacial loss and slow overall melting, hence promoting some level of re-stabilisation of the GrIS. This in turn would reduce the freshening of the North Atlantic.

Outlook

Critical transitions of these four tipping elements will have dramatic ecological and socio-economic consequences on a global scale. Their importance is such that a precautionary principle should be used in planning for the future, both in terms of decarbonisation but also in adaptation and resilience planning.

GrIS collapse will add 7m to sea levels, albeit over the next 1,000 years, but at an increasing rate in the relevant future. AMOC collapse will ruin European agriculture and make much of the housing and infrastructure untenable. Amazon die off will be an ecological disaster and pump even more carbon into the atmosphere, changing rainfall patterns and leaving a scar on the planet as testament to our vandalism. SAM collapse will ruin the continent’s agriculture with impacts far beyond the price of coffee and chocolate.

Early warning signals should be carefully researched and searched for to help society plan for these eventualities and the impacts they will bring. Wider knowledge of the importance of these systems and their growing fragility is also important.

1. Boers, N., Liu, T., Bathiany, S. et al. Destabilization of Earth system tipping elements. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01787-0

2. Beatriz Arellano-Nava et al., Recent and early 20th century destabilization of the subpolar North Atlantic recorded in bivalves.Sci. Adv.11,eadw3468(2025).DOI:10.1126/sciadv.adw3468