Approximately 720 million years ago, the world was encased in ice, frozen from pole to pole. This “Snowball Earth” – an uninhabitable planet, save for a few spots of refuge for bacteria along the equator – stayed frozen for about 80 million years before thawing out. Carbon dioxide had been bubbling from volcanoes and vents underneath the surface of the ice for millions of years.
Finally the carbon dioxide probably built up to 300 times today’s levels – surpassing a critical tipping point – and the greenhouse effect caused the ice sheets to melt. “We went out of the freezer and into the frying pan”, says Timothy Lenton, an Earth system scientist at the University of Exeter.
Since the unfreezing of Snowball Earth, multicellular life has emerged. Dinosaurs came and went. For the last tiny fraction of geological time, humans have populated the planet. If the Earth has been around for 24 hours, humans appeared in the last few seconds. In an even shorter amount of time, the industrial revolution has unfolded and human activities in parts of the world now put demands on natural systems across the globe in unprecedented ways.
Overfishing has led to the collapse of cod populations in the United Kingdom, Canada, and other Atlantic Ocean countries. Nitrogen and phosphorus from agricultural runoff have led to algal blooms that suck oxygen from lake waters and are sometimes toxic. And continued human-driven, or anthropogenic, global temperature rise has altered India’s summer monsoon patterns – Lenton and his colleagues speculate that the consequences of human activities will eventually turn the Amazon rain forest into savanna, and melt the ice sheets in Greenland and Antarctica.1
From a human-centred point of view, we are in danger of putting ourselves into a situation that seems nearly as untenable for our civilisation as Snowball Earth, and on a much faster timetable. As the habitable version of Earth spins on its tilted axis, the different systems contained within it – the biosphere, atmosphere, and geosphere – currently provide services vital to our survival and well-being.
But they can also shift at critical tipping points. A tipping point is where a system can flip and turn into something different. Reversing the actions that pushed the system to tip does not mean the system will tip back. And the scale at which these changes happen – from your back garden to the boundaries of the atmosphere – becomes important.
Identifying tipping points, researchers say, could help communities stave off potentially drastic changes in the future. Or it could help them push towards tipping points to create changes that might lead to more desirable circumstances.
Where did the term “tipping points” originate?
The idea of a tipping point had been around since the 19th century when French mathematician Henri Poincaré was studying the movement of celestial bodies and realised that systems could shift rapidly from one equilibrium to another. He didn’t call the point at which the system shifted a “tipping point”, but knew that systems could reach a critical point where they would bifurcate. Literally, systems come to a fork in the road and can follow one path or the other.
The recognition of tipping points runs counter to the idea of linear thinking, where one event leads to another. In a linear world view, effects are additive and predictable, and to a large extent reversible. The real world has shown us repeatedly that this is not the case. Tipping points are most visible in single events, but actually stem from the dynamics of multiple factors.
For example, the cod population of the Atlantic northwest collapsed in what was seemingly a single event of overfishing in the 1990s, but was actually the result of decades of overfishing by many fishing fleets, improvements in fishing technology, a growing market and demand for cod, and other factors. The ensuing fishing restrictions did not lead to a rapid recovery of the fish population and, 20-plus years on, it has still not returned to what it was.
Not until 1957 did Morton Grodzins, a political scientist at the University of Chicago, first formally use the phrase “tip point”. He used it to describe the threshold at which whites began to move out of a neighbourhood once African Americans started moving in.2 The first ecological application of a “tipping point” appeared approximately two decades later, when ecologist C. S. “Buzz” Holling was studying forests in Canada that were prone to spruce budworm infestations. In one possible state, predators could keep the destructive spruce budworms in check. In another, the pests could unleash their prowess by defoliating the forest and thrive until the trees died out. Holling was able to show that certain stressors could flip what seemed to be a stable ecosystem into an alternative state.
But the term wasn’t popularised until Malcolm Gladwell’s book The Tipping Pointwas published in 2000. In it, Gladwell highlighted myriad social examples where sudden and unexpected change made a big difference. For instance, he describes how epidemics of sexually transmitted diseases can take off because of the interactions of multiple conditions, from housing infrastructure to the availability of medical care.
While the concept had been around in the ecological sciences for decades, the climate science community didn’t use the term “tipping point” until after Gladwell’s book revived the phrase, first formalised in the scientific literature by Lenton and his colleagues in the mid-2000s. Then, in 2009, 28 leading scientists – including Lenton and Johan Rockström of the Stockholm Resilience Centre – identified nine “planetary boundaries” that mark conditions vital for human survival.3
The nine boundaries together represent an Earth system that maintains the functions and processes that have made it possible for humans to survive and thrive, particularly in the past 10,000 years, or the current geologic era called the Holocene. The researchers were able to quantify seven of them, and showed that we’ve crossed four: climate change, biodiversity loss, land-system change, and altered nitrogen and phosphorus flows to the biosphere and oceans. The planetary boundaries do not directly correspond to tipping points, instead they describe conditions that mean an increased risk of reaching them.
“We worked together to articulate that tipping points are possible, that it’d be good to study them, and any sensible approach to the future would at least account for them”, Lenton says.
In 2015, he and other researchers wrote that “perhaps the most ‘dangerous’ aspect of future climate change is the possibility that human activities will push parts of the climate system past tipping points, leading to irreversible impacts.”4 In light of this, Lenton believes it’s important to map out the early warning signals that can indicate that a system is close to tipping from one state into another.
If the tipping points in different systems can be identified, then individuals, policy makers, and communities can conceivably change their actions to prevent reaching these tipping points altogether. And, if there’s no way to avoid the tipping points, the stakeholders can take action to absorb the consequences once system A tips into system B. “A trivial investment in the millions [for an early detection system] could warn us of something that could hurt us in the trillions”, Lenton says.
Early warnings, however, rely on understanding the feedbacks in a system that shape it and that could cause it to tip. That can be difficult. “When you get closer to a tipping point, your system will become more variable”, says Oonsie Biggs, a researcher at the Stockholm Resilience Centre. “It can be very unclear as to where the system is going.”
Tipping points in practice
“People are generally managing systems like there are no thresholds”, says Biggs. She thinks that it is “better to assume that there are many of these thresholds and what they may be rather than assume that there are none.”
In her research, Biggs and her colleagues have studied multiple ecological systems that have tipped from one state into another and documented these instances in the Regime Shifts DataBase.5 By understanding how shifts can happen in certain systems, people can get a better sense of the conditions under which they occur, and ultimately be able to influence how those systems are managed to avoid reaching tipping points – or to push towards them, Biggs says.
Avoiding undesirable thresholds or tipping points requires resilience. Resilience describes the capacity of a system – be it an individual, lake, forest, city, or economy – to deal with disturbance, change, and development, through persistance, adaptation, or transformation. Resilience in itself, however, is neither a good nor a bad thing.
“You may value some components of an ecosystem whereas other people value different components of an ecosystem”, says Anne Salomon, a marine ecologist at Simon Fraser University in Burnaby, Canada. “It’s not a matter of good or bad, it’s a matter of difference.” Asking questions about the specific context helps clarify wanted outcomes: resilience of what system, to what tipping point, and for whom?
Resilience thinking, then, embraces the idea that humans and nature are so inextricably intertwined that they should be thought of cohesively as one social-ecological system. It describes an approach for looking at systems, how they function, how they are perturbed, and what drives the behaviour that causes such perturbations.Resilience researchers have proposed seven principles that contribute to building resilience to minimise risk of hitting undesirable social-ecological tipping points. For instance, having more diversity in a system could give it a greater capacity to deal with change. Having connectivity between different elements in a system could also offset potential disturbances. “But you don’t want to be overconnected”, says Biggs, pointing to the risk of diseases, pests, or other unwanted epidemics spreading far and fast. Learning about a system and building social trust in it, as well as the willingness to act, can also be vital. “If this foundation is laid before a crisis, you can just draw on social resources or capital to act in a coherent way”, she says.
In South Africa’s national parks, for example, scientists, park managers, and rangers have come together to identify the potential thresholds in ecosystems to lay a foundation to manage the fish in their rivers, their elephant populations, savanna ecosystems, and the spread of fire. By identifying potential tipping points, rangers and managers can then look for indicators to monitor the activity in their ecosystems of interest. If they see anything alarming, “then they will have a management meeting where they make a decision to avoid hitting the threshold or to reverse the course of activity”, says Biggs.
Tipping for good
While much attention has been paid to “negative” tipping points – that is, when a stable equilibrium suddenly reaches a critical point and changes into something else entirely – an equal amount of attention might be necessary in investigating “positive” tipping points, or the restoration of a particular ecosystem.
Ecologist Gerry Marten founded the EcoTipping Points Project in 2004 and the website highlights only positive cases where communities were able to steer away from critical tipping points. The project has documented how a marine sanctuary at Apo Island in the Philippines overturned decades of overfishing to restore the island’s coral reef ecosystem and fishery; how villages in Thailand and indigenous communities in southern Mexico reversed their patterns of deforestation; and how cotton farmers all around India upended a cycle of pesticide resistance by using other pest control methods.
The featured stories share similar ingredients for success, such as genuine community participation, the co-adaptation of a community and ecosystem, and allowing nature to run its course and unveil its capacity for self-organisation and restoration. “The main ingredients for success centre around the characteristics of the technology that enable things to be turned around, and the second is about the social organisation for making these changes happen”, says Marten. And the biggest barriers, according to Marten, are overcoming social obstacles that stand in the way of tipping a system back.
As humans can derive value from different states of a system, we may want to control which way a system tips. “The health of an ecosystem is in the eye of the beholder”, says Salomon of Simon Fraser University. “Health is a normative term, depending on what you want from an ecosystem.” Salomon has gathered some insights into resilience thinking from studying kelp forests – the “poster child of tipping points”, she says – along the British Columbia coast. Kelp forests are known to switch dramatically between forested and deforested states, and communities along the coast have maintained a mosaic of both states.
In one state, a rocky reef could have what looks like a liquid forest made of kelp floating above it. In another, the kelp is gone and sea urchins cover the rocky reefs. Depending on how humans enact laws or practices that modify the populations of sea otters, which are known to prey on sea urchins, the reefs can either be lush and green, or rocky and seemingly barren. But because coastal communities derive value from both kelp and sea urchins – urchins can be harvested and sold commercially, whereas kelp provides a habitat for fish and shellfish – they have maintained a patchwork of forested and deforested states by controlling the hunting of sea otters.
What Salomon has learned from transforming the state of kelp forests from one state to another ties back to the fundamentals of resilience in social-ecological systems. “It’s recognising that humans are just one component of a complex system with strong feedbacks and interactions, recognising the ecological and social interactions within these complex systems, and then collaboratively figuring out how to change our governance of the systems and how we interact with them to get them to a desirable state”, she says.
Seeing tipping points before they tip
Tipping points happen at many levels, from sea urchins and kelp forests to the entire planet’s atmosphere. We know that a Snowball Earth is not good for humans. We also know the same is true for global warming. One conceivable future resulting from climate change would be one where the Sahara desert could be a greener, wetter place with more vegetation – which could be good news for farmers and herders in the region. But elsewhere, people will suffer, as climate change also leads to large and irreversible sea-level rise that will wipe out whole island nations, as well as large deltas where humans have tended to settle over multiple generations.
What risks are societies willing to accept – and which ones can actually be foretold in a chaotic and non-linear world? Seeing tipping points could give some actors, whether they are policymakers, corporations, or communities, the power to change course. But can tipping points actually be identified?6
While we can conceive of futures caused by climate change, pinpointing the exact moments that, for instance, will lead to the greening of the Sahara, or the reversal of ocean currents, might be more difficult. Acknowledging, and maybe even identifying, tipping points in the social-ecological systems in which people live and on which they depend means having a better chance of modifying behaviour to tip the scales for the outcomes people want.