What are climate tipping points and how might they affect the UK?

DOI: https://doi.org/10.58248/RR101

In 2025, Earth was around 1.44°C warmer than during the pre-industrial period. As global warming approaches 1.5°C, parts of the climate system are at increasing risk of undergoing potentially abrupt, long-lived and irreversible shifts. These shifts are known as ‘tipping points’ and have the potential to disrupt ecosystems, alter weather patterns, accelerate sea-level rise and increase global warming.

Several tipping point thresholds could be crossed if there is between 1.5°C and 2°C of sustained global warming, and the likelihood of additional tipping points being crossed would increase with further warming.

However, tipping points’ precise thresholds, likelihoods and timescales remain unclear. This briefing summarises the climate tipping points that would be most likely to affect the UK if their thresholds were crossed and assesses the scientific evidence for when this could happen.

What are climate tipping points?

In broad terms, a climate tipping point is a critical threshold in a part of the climate system (known as a ‘tipping element’; for example, the Amazon rainforest) in which a small change becomes self-sustaining and leads to a large shift in the state of that climate system. If a tipping point is crossed, it can alter the climate system and – in some cases – accelerate global warming further.

Tipping point theory emerged as a concept in climate science in the mid-2000s and is now an area of increasing public concern. It should be noted that the definition of ‘tipping point’ varies widely, and that the term is often misapplied.

Most proposed climate tipping points have large-scale consequences (either regional or global; figure 1) and result in changes that are irreversible, at least over human timescales. Although some tipping point thresholds may soon be reached, for  tipping to begin requires global warming levels to be sustained for a given time. The full effects of a tipping point being crossed may unfold over different timescales, ranging from decades, to centuries, to millennia.

Crucial tipping points in the climate system

Tipping points occur across interconnected parts of Earth’s natural systems and at least 16 different tipping points have been identified. Tipping points can happen in isolation, but they can also interact, and one system becoming destabilised can increase the risk of another system becoming destabilised. For example, an inflow of meltwater from the Greenland Ice Sheet could destabilise ocean currents in the Atlantic Ocean.

Scientists warn of negative environmental and socio-economic consequences if tipping point thresholds are crossed. Five important tipping points are summarised below.

Mass loss of warm-water coral reefs

The UK is responsible for the 12th–largest area of coral reefs of any country in the world, thanks to its Overseas Territories. Globally, coral reefs are crucial to the wellbeing of over half a billion people and play a vital role in ocean ecosystems. Warming has increased the frequency of coral bleaching (when corals lose algae living in their tissue, causing the coral to turn completely white). In turn, coral bleaching can lead to coral death and eventually reef ecosystem collapse.

The Intergovernmental Panel on Climate Change projects that 70% to 90% of today’s warm-water reefs will disappear with 1.5°C of warming. Estimates vary, but scientists believe that widespread coral reef tipping could occur between 1.0°C and either 1.5°C of sustained global warming or 2.0°C of sustained global warming. Reef collapse takes around a decade but will start at different times in different regions.

Dieback of the Amazon rainforest

The Amazon rainforest is a biodiversity hotspot and a natural carbon sink. It also helps sustain itself by recycling rainfall, but forest loss risks triggering self-sustaining drying and dieback instead. Widespread dieback would increase global warming by 0.1°C: the equivalent of around 5 years of current human emissions. Scientists believe that Amazon rainforest dieback would be possible at 2 °C of sustained global warming and likely beyond 3.5 °C. However, in combination with deforestation, Amazon rainforest dieback could start below 2°C of global warming. These changes would play out over decades or centuries.

Abrupt permafrost thaw

Permafrost refers to permanently frozen soils and sediments typically found in the Arctic and Siberia. When permafrost thaws, it releases carbon dioxide and other greenhouse gases back into the atmosphere, amplifying global warming. Permafrost can undergo:

• gradual thaw
• localised abrupt thaw, or
• possibly, a large-scale collapse (but this is debated) (PDF)

If global warming is sustained at around 1.5°C, widespread abrupt thaw and associated greenhouse gas release is likely. Wider gradual and some localised abrupt thaw is already happening and any tipping would play out over multiple centuries.

Atlantic Ocean circulation

The Atlantic Meridional Overturning Circulation (AMOC) is an important current in the Atlantic Ocean that transports warm waters northward before cooling, sinking and returning southward. The subpolar gyre is a related system of rotating ocean currents in the North Atlantic Ocean. Both systems are closely connected and help maintain mild climates in Europe.

Evidence from the geological record suggests that the AMOC has collapsed before. However, its future is uncertain, with AMOC collapse possible – but not guaranteed – at 1.4°C to 8°C of sustained global warming. AMOC collapse would make Europe much colder and drier than currently projected. It would also dramatically shift tropical monsoons, which would reduce global food security. Any changes related to the collapse of the AMOC would play out over decades to centuries.

Convection in the subpolar gyre could collapse between 1.1°C and 3.8°C of sustained global warming. Such a collapse could occur over a decade.

Collapse of the Greenland Ice Sheet and/or the West Antarctic Ice Sheet

The Greenland Ice Sheet is shrinking and may be approaching a tipping point in west Greenland. The West Antarctic Ice Sheet is also highly vulnerable to warming and some climate models suggest irreversible ice sheet loss may have started.

Collapse of both ice sheets is already possible beyond 1°C of sustained global warming and becomes likely beyond 1.5 °C. Together, they could increase sea levels by up to around 12 metres over thousands of years. Collapse of the ice sheets would also accelerate sea-level rise in the coming decades, threatening coastal regions far sooner than expected today. Collapse of the ice sheets could also make the AMOC more likely to cross its tipping point threshold.

Have we crossed any tipping points?

It is possible that we have crossed the tipping point threshold for warm-water coral reefs. Without stringent mitigation, warm-water coral reefs would likely be committed to die off on a significant scale within the next 10 years.

Scientists believe that widespread abrupt permafrost thaw, disintegration of the Greenland Ice Sheet and the West Antarctic Ice Sheet, and potentially the collapse of subpolar gyre convection are:

• possible at current global warming levels
• likely beyond 1.5°C of sustained global warming

Scientists believe that the complete collapse of the AMOC during this century is unlikely. However, they expect the AMOC to weaken substantially, and a tipping point threshold committing the AMOC to later collapse may be crossed within decades.

So far, dieback in the Amazon has been localised, but passing 1.5°C of sustained global warming, along with intensified deforestation, could lead to regional dieback.

How do we recognise an approaching tipping point?

Early warning signals rely on a phenomenon known as ‘critical slowing down’. As a system loses resilience, it takes longer to recover from disturbances, and its fluctuations often become larger and more persistent. For example, more than 75% of the Amazon rainforest was assessed as having lost resilience since the early 2000s. Detecting these signals requires long-term monitoring, such as continuous satellite observations and in-situ measurements. However, resilience loss does not necessarily mean a tipping point threshold will be crossed.

Geological reconstructions, from archives such as Greenland ice core records, provide evidence of tipping points being crossed in Earth’s history. These can be used to make inferences about the mechanism(s) behind past changes and are relevant for projecting the future.

Which tipping points would be most likely to affect the UK?

The tipping points that would be most likely to affect the UK if they were crossed would be changes in Atlantic Ocean circulation and the collapse of the West Antarctic Ice Sheet.

Atlantic Ocean circulation

AMOC collapse could make the UK and Europe much colder and drier than currently projected . This could likely have a detrimental effect on the UK’s domestic food production and induce widespread cessation of arable farming in the UK. AMOC collapse could also affect the UK indirectly by disrupting international food security.

Subpolar gyre collapse could induce between 2°C and 3°C of cooling over the North Atlantic. The potential agricultural effects on the UK remain unquantified.

Sea-level rise

Collapse of the West Antarctic Ice Sheet could cause up to 3 meters of sea level rise over centuries. However, it would also accelerate sea-level rise over the coming decades, which would expose UK estuaries and coasts to tidal flooding and have the potential to damage or overcome infrastructure.

Other tipping points

Warm-water reef collapse could lead to reduced coastal protection, declining food security and a loss of tourism income. These changes would directly affect the UK Oversees Territories. Permafrost thaw and Amazon dieback would not directly affect the UK, but they would have an indirect effect by increasing the magnitude of global warming.

What is being done to reduce the risk of tipping points being crossed?

There are a range of international and domestic commitments that aim to reduce the risk of tipping points being crossed.

International commitments

The Paris Agreement requires signatory countries to keep global warming well below 2°C above pre-industrial levels and to pursue efforts to limit warming to 1.5°C. Achieving this globally would reduce the potential risk of crossing tipping point thresholds.

National commitments

The UK Government’s third National Adaptation Programme includes action on international climate risk. However, successive Climate Change Committee assessments have said that “no [UK] sectors are yet well adapted to the risks of climate change”, let alone the risk posed by tipping points.

To begin to address the risk posed by tipping points, the UK Government’s Advanced Research and Invention Agency (ARIA) recently allocated £81 million to develop a proof-of-concept early warning system and new models to monitor the Greenland Ice Sheet and the subpolar gyre.

Acknowledgements

Dr Gordon Inglis is a Royal Society Dorothy Hodgkin Fellow (2020-2028) and Principal Research Fellow in the School of Ocean and Earth Science at the University of Southampton.

Dr David Armstrong McKay is a Lecturer (Assistant Professor) in Geography, Climate Change and Society at University of Sussex’s School of Global Studies.

POST is grateful to the authors for kindly giving their time to produce this briefing and the Royal Society for identifying possible authors.

Questions about this briefing should be referred to Jonathan Wentworth ([email protected]), who acted as parliamentary lead for this work.