Tipping points: How we talk about climate change in the Earth system
Humans influence the planet like no other living species. The way we live, the technologies we use, and the way we produce food now affect almost every part of the Earth system. Where do we need to take decisive action to prevent critical changes?
Self-sustaining changes
Scientists around the world are observing how these changes unfold and what effects they have. What they are finding is that the Earth system does not always respond in proportion to the forces acting on it. Some parts of the Earth system reach a critical state beyond which their structure and function continue to change even without the original external driver. Once set in motion, these changes continue on their own. They may accelerate, intensify, or reach unforeseen proportions.
Many researchers refer to the point at which a change begins to continue on its own as a system’s tipping point. It is characterized by a threshold. The Greenland Ice Sheet provides one example: if its thickness falls below a critical level, the ice will continue to melt even without further global warming. Scientists use the term climate tipping elements for parts of the global climate system that enter a state of self-sustaining change once a certain level of global warming is reached. Their tipping point therefore corresponds to a particular global average temperature.
Gerrit Lohmann, an expert in climate dynamics at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), cautions against using the term too loosely. “Talking about a tipping point gives the impression that the threshold can be precisely defined, as though a particular temperature or CO₂ level would automatically trigger an abrupt shift,” he says. But transitions between states in the climate system do not necessarily occur at a fixed value. “The climate is a highly complex, stochastic system. It undergoes natural fluctuations that can cause large swings. And systems can tip sooner or later depending on random variations, weather events, and internal feedbacks.” Lohmann and many other researchers therefore prefer to speak of “critical ranges” rather than tipping points. “We do not want to suggest a degree of precision that the research cannot provide.”
Processes amplify or counteract one another
Feedback mechanisms play an important role in the nonlinear processes of change in tipping systems. They can amplify or accelerate processes both before and after tipping occurs. The Greenland Ice Sheet, for example, melts faster the thinner it becomes. This is because melting lowers its surface into progressively warmer layers of air, causing it to melt even more rapidly. Some feedbacks also counteract changes set in motion by global warming. Feedbacks, and particularly amplifying ones, make these changes all the more consequential for humanity and more difficult for researchers to predict. Individual feedback effects can be simulated in models to some extent. In reality, however, many mechanisms operate simultaneously in different parts of the Earth system, such as the atmosphere, ocean, soil, and biosphere, and interact with one another.
No return in the foreseeable future
Once triggered, processes in a system that has tipped continue under their own momentum. Even if the external conditions that existed before tipping were restored, the system may be unable to return to its original state. So even if the global average temperature were to fall back to preindustrial levels in the future, a melting Greenland or West Antarctic Ice Sheet would not grow back. This is what is meant when the tipping of certain parts of the Earth system is described as irreversible. Different parts of the climate system respond to global warming on different timescales. In the short term, over periods ranging from years to decades, weather patterns, sea ice, and climate patterns change. Over the longer term, spanning centuries to millennia, major ocean currents, ice sheets, and carbon storage, for example in the ocean, forests, peatlands, and permafrost, are affected.
Preventive strategies require a nuanced understanding of risk
Once a tipping element in the climate system has embarked on a path of change, it becomes difficult to change its course. This is why it is important to identify and understand tipping elements, such as the Greenland Ice Sheet, and their dynamics: a system may reach its tipping point long before the full extent of the resulting changes becomes apparent. The impacts may unfold over timescales far beyond the span of human generations on which political and societal planning is usually based. To develop strategies that can prevent a system from tipping or enable adaptation to its consequences, societies and policymakers need an understanding of risk that takes these dynamics into account.
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Tipping cascades
Many of the Earth system’s known tipping elements are closely interconnected. If one tips, it can affect other parts of the Earth system in ways that cause them to reach their own tipping points more quickly. Researchers refer to this knock-on effect as a tipping cascade. One example is the interaction between the Greenland Ice Sheet and the Atlantic Meridional Overturning Circulation (AMOC). Meltwater from the ice sheet affects the AMOC, which in turn shapes the climate across large parts of Europe, Africa, and the Americas. If the Greenland Ice Sheet were to melt substantially or even completely, there are concerns that the AMOC could weaken significantly. This enormous ocean circulation system is a key component of the global climate system. A weakening of the AMOC would alter ocean dynamics and atmospheric circulation around the world and, consequently, affect carbon stores such as forests and peatlands. At the same time, like other parts of the climate system, this ocean circulation naturally fluctuates and exhibits considerable variability. This makes a potential tipping event difficult to predict.
Other systems thought to be capable of tipping are also important climate regulators that influence the global climate. Permafrost in the far north, for example, represents an important carbon store. Healthy forests and peatlands can actively absorb CO₂. They are therefore not only indicators of a changing climate, they also influence how the climate develops.
Reading the warning signs: Signs of approaching tipping
Some research focuses on identifying early indications that a climate system or ecosystem may be approaching a tipping point. Scientists analyze observational data, for example, to determine whether a system is becoming progressively less able to recover from external disturbances. A forest, coral reef, or mountain glacier may recover from damage following a period of extreme heat if it has enough time and favorable conditions to do so. But if heat events occur at increasingly short intervals, there may not be enough time or sufficient resources for recovery. Declining resilience, that is, a reduced ability to withstand disturbances or recover from them, is considered a warning sign. It may indicate that a system is at risk of tipping, whether relatively gradually or abruptly.
How many tipping systems are there?
Researchers have used different definitions of tipping systems in the scientific literature to date. These definitions differ, for example, in whether changes after tipping are considered irreversible and whether the transition occurs abruptly. As a result, there is no fixed number of known tipping elements. Many Earth system scientists are working to identify which of Earth’s subsystems display characteristics of tipping dynamics, in other words, which could undergo abrupt and potentially irreversible change. The search for possible tipping elements is based on three main pillars: ongoing observations and recorded data, paleontological and geological evidence, and computer-based models of parts of the Earth system. These approaches allow researchers to assess the current state of a subsystem of the global climate, reconstruct aspects of its past development where possible, and explore potential future trajectories.
Terminology used in communication
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- Tipping point: A critical threshold that, once crossed, often leads to abrupt and sometimes irreversible changes.
- Tipping system: A general term for systems that, in response to external influences, often shift abruptly into a state that is at least partly irreversible, for example, a chair tipping over.
- Tipping element: The term was coined in discussions of tipping systems within the Earth system. A tipping element generally refers to an individual part of the climate system that, once a particular threshold is crossed, often shifts abruptly into a partly irreversible state, such as a rainforest or an ice sheet.
Tipping points have become a central, but also much-debated, concept in the climate discussion. Research in this area is still relatively young, and many findings remain preliminary. What we do know is that processes within the climate system can respond to external influences in ways that are difficult to predict. Assumptions about potential tipping points are based partly on evidence from Earth’s geological past and largely on computer-based modeling of parts of the Earth system. Many processes and their interactions are still only partially understood, while feedback effects and delayed responses are not yet sufficiently well understood to reliably predict the timing and consequences of change. What is clear is that global warming can dramatically alter habitats and living conditions for both people and the natural environment. These changes may unfold over shorter or longer periods. This also means that some of the consequences will be experienced by us, our children, and our grandchildren, while others will unfold over thousands of years.
There is also debate about what communication about tipping elements can or should achieve. For many researchers, the primary objective is to provide comprehensive, evidence-based information about the potential risks of climate change. This effort to raise awareness is often accompanied by an appeal to decision-makers in politics and society: to do everything possible to prevent further global warming and to prepare in good time for changing living conditions.
Many changes in the climate occur gradually. Their impacts are already serious enough to demand immediate action. But it is also important to understand the nonlinear processes that can occur within the climate system. Gerrit Lohmann believes that the concept of climate tipping points can help with this. “Even though we cannot predict tipping points precisely, they illustrate how abruptly profound climate changes can occur,” he says. “And once a tipping point has been reached, we have lost the opportunity to adapt gradually to changing living conditions.” The concept therefore highlights the importance of addressing climate change early and with an eye to the future. “It shows that the Earth system is vulnerable, that the consequences of climate change can affect many generations, and that early, decisive action can make the greatest difference.”
At the same time, communication about climate tipping points requires careful judgment. In the worst case, the prospect of abrupt and unstoppable change could leave people paralyzed by fear. Resignation could then lead to inaction. But the opposite impression is equally unhelpful: people may assume that they-and the planet-remain in a safe zone as long as no tipping point has been reached. “But we left the safe zone long ago,” says Gerrit Lohmann. More than ever, it is now crucial to mobilize and combine society’s efforts to counter further climate change-regardless of whether changes occur abruptly or gradually.
Clear and transparent communication about the risks of climate change can help governments and municipalities adapt infrastructure, planning, and social practices in good time-before options for action are irretrievably lost. What is clear is that every increment of global warming increases the risk of severe, unforeseeable, and in some cases irreversible consequences, and that humanity must now address adaptation to a changing climate. “We should describe more concrete scenarios for the future,” Lohmann says, “so that we can develop concrete options for action.”
Tipping points in technology, the economy, and society
The discussion is not limited to tipping points in the natural climate system. Tipping points can also occur in other areas that may be crucial to climate action, including technological development, economic systems, and society. A new technology, for example, may cross a tipping point once essential components begin to be mass-produced. This can be seen with solar cells and batteries. The more people involved in manufacturing them and the greater the quantities produced, the faster practical knowledge and expertise in the production process grow. Processes become more efficient and therefore less expensive. Step by step, the technology moves closer to another tipping point - an economic one. Once a new technology becomes available at the same price as the technology it is intended to replace, its spread can become difficult to stop, and it may ultimately displace the older technology.
Self-reinforcing and cross-sector effects
As in the climate system, self-reinforcing mechanisms play an important role in bringing technological and economic development processes to a tipping point. If, for example, a company powers the production of solar panels using electricity generated by its own solar installations, production not only becomes more climate-friendly but also less expensive. More solar cells can then be produced and sold at lower prices. This stimulates demand, and an increasing amount of electricity is generated from solar energy.
Cross-sector effects also play a role, for example between the energy and transportation sectors. Electric vehicles can complement energy infrastructure by serving as mobile, flexible electricity storage systems. In this way, they can facilitate the use of wind and solar power, which varies depending on the time of day and weather conditions. The more electric vehicles are used as temporary storage, the easier it becomes to integrate more energy from climate-friendly sources - and the more climate-friendly transportation can become as well.
Governments are called upon to actively identify climate- and environmentally friendly innovations and specifically support their development, market entry, and wider adoption. Modular systems such as solar technology are particularly promising because their use can now be scaled almost without limit. Whether installed on a single-family home, deployed at the neighborhood level, or used in a centralized power plant, the basic components used to generate electricity are essentially the same.
When the new becomes normal
In addition to technological and economic tipping points, researchers also study social tipping points. The term describes moments when changes in norms, attitudes, or behavior within groups or entire societies become sufficiently widespread and deeply rooted to bring about lasting changes in established practices. This usually requires a critical share of the population to adopt a new technology, lifestyle, or perspective. When around 20 percent of a society uses a particular technology, for example, a threshold is often crossed after which the majority begins to adopt it as well. Whether this happens depends, among other things, on communication with and perceptions of so-called early adopters, the more risk-tolerant minority who are the first to try innovative ideas. If their behavior is viewed positively and as something worth emulating, the new practice has a good chance of moving from the exceptional to the new normal.
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Positive social tipping points, such as a shift toward predominantly plant-based diets, could help counter the progression of climate change. A key challenge will be to better understand how social norms change and how they can be used as leverage to establish climate-friendly behavior more broadly across society.
Scientific review and consultation:
Prof. Dr. Gerrit Lohmann, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
