According to the paradigm, "transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems." The Earth system process boundaries mark the safe zone for the planet to the extent that they are not crossed. As of 2009, two boundaries have already been crossed, while others are in imminent danger of being crossed.
In 2015, a second paper was published in Science to update the Planetary Boundaries concept including regional boundaries and findings were presented at the World Economic Forum in Davos, January 2015.
Planetary boundaries diagram of 2009.
A 2018 study, co-authored by Rockström, calls into question the international agreement to limit warming to 2 degrees above pre-industrial temperatures set forth in the Paris Agreement. The scientists raise the possibility that even if greenhouse gas emissions are substantially reduced to limit warming to 2 degrees, that might be the "threshold" at which self-reinforcing climate feedbacks add additional warming until the climate system stabilizes in a hothouse climate state. This would make parts of the world uninhabitable, raise sea levels by up to 60 metres (200 ft), and raise temperatures by 4–5 °C (7.2–9.0 °F) to levels that are higher than any interglacial period in the past 1.2 million years. Rockström notes that whether this would occur "is one of the most existential questions in science." Study author Katherine Richardson stresses, "We note that the Earth has never in its history had a quasi-stable state that is around 2 °C warmer than the preindustrial and suggest that there is substantial risk that the system, itself, will ‘want’ to continue warming because of all of these other processes – even if we stop emissions. This implies not only reducing emissions but much more.”
The planet Earth is a finite system, which means it has limits.
The idea that our planet has limits, including the burden placed upon it by human activities, has been around for some time. In 1972, The Limits to Growth was published. It presented a model in which five variables: world population, industrialization, pollution, food production, and resources depletion, are examined, and considered to grow exponentially, whereas the ability of technology to increase resources availability is only linear. Subsequently, the report was widely dismissed, particularly by economists and businessmen, and it has often been claimed that history has proved the projections to be incorrect. In 2008, Graham Turner from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) published "A comparison of The Limits to Growth with thirty years of reality". Turner found that the observed historical data from 1970 to 2000 closely matches the simulated results of the "standard run" limits of growth model for almost all the outputs reported. "The comparison is well within uncertainty bounds of nearly all the data in terms of both magnitude and the trends over time." Turner also examined a number of reports, particularly by economists, which over the years have purported to discredit the limits-to-growth model. Turner says these reports are flawed, and reflect misunderstandings about the model. In 2010, Nørgård, Peet and Ragnarsdóttir called the book a "pioneering report", and said that it "has withstood the test of time and, indeed, has only become more relevant."
With few exceptions, economics as a discipline has been dominated by a perception of living in an unlimited world, where resource and pollution problems in one area were solved by moving resources or people to other parts. The very hint of any global limitation as suggested in the report The Limits to Growth was met with disbelief and rejection by businesses and most economists. However, this conclusion was mostly based on false premises.
Of a different kind is the approach made by James Lovelock. In the 1970s he and microbiologistLynn Margulis presented the Gaia theory or hypothesis, that states that all organisms and their inorganic surroundings on Earth are integrated into a single self-regulating system. The system has the ability to react to perturbations or deviations, much like a living organism adjusts its regulation mechanisms to accommodate environmental changes such as temperature (homeostasis). Nevertheless, this capacity has limits. For instance, when a living organism is subjected to a temperature that is lower or higher than its living range, it can perish because its regulating mechanism cannot make the necessary adjustments. Similarly the Earth may not be able to react to large deviations in critical parameters. In his book The Revenge of Gaia, he affirms that the destruction of rainforests and biodiversity, compounded with the increase of greenhouse gases made by humans, is producing global warming.
Our planet’s ability to provide an accommodating environment for humanity is being challenged by our own activities. The environment—our life-support system—is changing rapidly from the stable Holocene state of the last 12,000 years, during which we developed agriculture, villages, cities, and contemporary civilizations, to an unknown future state of significantly different conditions.
The Holocene began about 10,000 years ago. It is the current interglacial period, and it has proven to be a relatively stable environment of the Earth. There have been natural environmental fluctuations during the Holocene, but the key atmospheric and biogeochemical parameters have been relatively stable. This stability and resilience has allowed agriculture to develop and complex societies to thrive. According to Rockström et al., we "have now become so dependent on those investments for our way of life, and how we have organized society, technologies, and economies around them, that we must take the range within which Earth System processes varied in the Holocene as a scientific reference point for a desirable planetary state."
Since the industrial revolution, according to Paul Crutzen, Will Steffen and others, the planet has entered a new epoch, the Anthropocene. In the Anthropocene, humans have become the main agents of not only change to the Earth System  but also the driver of Earth System rupture, disruption of the Earth System's ability to be resilience and recover from that change. There have been well publicized scientific warnings about risks in the areas of climate change and stratospheric ozone. However, other biophysical Earth System processes are also important and have limits which are being exceeded. For example, since the advent of the Anthropocene, the rate at which species are being extinguished has increased over 100 times, and humans are now the driving force altering global river flows as well as water vapor flows from the land surface. Continuing pressure on the Earth System from human activities raises the possibility that further pressure could be destabilizing, and precipitate sudden or irreversible responses by the Earth System, shunting it towards a variation or mode that is dangerous to life including to human society, for example a Hothouse Earth mode. According to Rockström et al., "Up to 30% of all mammal, bird, and amphibian species will be threatened with extinction this century." It is difficult to restore a 'safe operating space' for humanity that is described by the planetary boundary concept, because the predominant paradigms of social and economic development are largely indifferent to the looming possibilities of large scale environmental disasters triggered by humans. Legal boundaries can help keep human activities in check, but are only as effective as the political will to make and enforce them.
Thresholds and boundaries
The threshold, or tipping point, is the value at which a very small increment for the control variable (like CO2) triggers a larger, possibly catastrophic, change in the response variable (global warming) through feedbacks in the natural Earth System itself.
The threshold points are difficult to locate, because the Earth System is very complex. Instead of defining the threshold value, the study establishes a range, and the threshold is supposed to lie inside it. The lower end of that range is defined as the boundary. Therefore, it defines a 'safe operating space', in the sense that as long as we are below the boundary, we are below the threshold value. If the boundary is crossed, we enter into a danger zone.
The proposed framework lays the groundwork for shifting approach to governance and management, away from the essentially sectoral analyses of limits to growth aimed at minimizing negative externalities, toward the estimation of the safe space for human development. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" for humanity if major human-induced environmental change on a global scale is to be avoided
Transgressing one or more planetary boundaries may be highly damaging or even catastrophic, due to the risk of crossing thresholds that trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. The 2009 study identified nine planetary boundaries and, drawing on current scientific understanding, the researchers proposed quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere < 350 ppm and/or a maximum change of +1 W/m2 in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (less than 5% reduction in total atmospheric O3 from a pre-industrial level of 290 Dobson Units); biogeochemicalnitrogen (N) cycle (limit industrial and agricultural fixation of N2 to 35 Tg N/yr) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P); global freshwater use (< 4000 km3/yr of consumptive use of runoff resources); land system change (< 15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of < 10 extinctions per million species). The two additional planetary boundaries for which the group had not yet been able to determine a global boundary level are chemical pollution and atmospheric aerosol loading.
Subsequent work on planetary boundaries  begins to relate these thresholds at the regional scale.
Science indicates that we are transgressing planetary boundaries that have kept civilization safe for the past 10,000 years. Evidence is growing that human pressures are starting to overwhelm the Earth’s buffering capacity. Humans are now the most significant driver of global change, propelling the planet into a new geological epoch, the Anthropocene. We can no longer exclude the possibility that our collective actions will trigger tipping points, risking abrupt and irreversible consequences for human communities and ecological systems.
Christopher Field, director of the Carnegie Institution's Department of Global Ecology, is impressed: "This kind of work is critically important. Overall, this is an impressive attempt to define a safety zone." But the conservation biologist Stuart Pimm is not impressed: "I don’t think this is in any way a useful way of thinking about things... The notion of a single boundary is just devoid of serious content. In what way is an extinction rate 10 times the background rate acceptable?" and the environmental policy analyst Bill Clark thinks: "Tipping points in the earth system are dense, unpredictable... and unlikely to be avoidable through early warning indicators. It follows that... 'safe operating spaces' and 'planetary boundaries' are thus highly suspect and potentially the new 'opiates'."
The biogeochemist William Schlesinger queries whether thresholds are a good idea for pollutions at all. He thinks waiting until we near some suggested limit will just permit us to continue to a point where it is too late. "Management based on thresholds, although attractive in its simplicity, allows pernicious, slow and diffuse degradation to persist nearly indefinitely."
The hydrologist David Molden thinks planetary boundaries are a welcome new approach in the 'limits to growth' debate. "As a scientific organizing principle, the concept has many strengths ... the numbers are important because they provide targets for policymakers, giving a clear indication of the magnitude and direction of change. They also provide benchmarks and direction for science. As we improve our understanding of Earth processes and complex inter-relationships, these benchmarks can and will be updated ... we now have a tool we can use to help us think more deeply—and urgently—about planetary limits and the critical actions we have to take."
The ocean chemist Peter Brewer queries whether it is "truly useful to create a list of environmental limits without serious plans for how they may be achieved ... they may become just another stick to beat citizens with. Disruption of the global nitrogen cycle is one clear example: it is likely that a large fraction of people on Earth would not be alive today without the artificial production of fertilizer. How can such ethical and economic issues be matched with a simple call to set limits? ... food is not optional."
The environment advisor Steve Bass says the "description of planetary boundaries is a sound idea. We need to know how to live within the unusually stable conditions of our present Holocene period and not do anything that causes irreversible environmental change ... Their paper has profound implications for future governance systems, offering some of the 'wiring' needed to link governance of national and global economies with governance of the environment and natural resources. The planetary boundaries concept should enable policymakers to understand more clearly that, like human rights and representative government, environmental change knows no borders."
The climate change policy advisor Adele Morris thinks that price-based policies are also needed to avoid political and economic thresholds. "Staying within a 'safe operating space' will require staying within all the relevant boundaries, including the electorate’s willingness to pay."
In summary, the planetary boundary concept is a very important one, and its proposal should now be followed by discussions of the connections between the various boundaries and of their association with other concepts such as the 'limits to growth'. Importantly, this novel concept highlights the risk of reaching thresholds or tipping points for non-linear or abrupt changes in Earth-system processes. As such, it can help society to reach the agreements required for dealing effectively with existing global environmental threats, such as climate change.
In their report (2012) entitled "Resilient People, Resilient Planet: A future worth choosing", The High-level Panel on Global Sustainability called for bold global efforts, "including launching a major global scientific initiative, to strengthen the interface between science and policy. We must define, through science, what scientists refer to as "planetary boundaries", "environmental thresholds" and "tipping points"."
In 2011, at their second meeting, the High-level Panel on Global Sustainability of the United Nations had incorporated the concept of planetary boundaries into their framework, stating that their goal was: "To eradicate poverty and reduce inequality, make growth inclusive, and production and consumption more sustainable while combating climate change and respecting the range of other planetary boundaries."
Elsewhere in their proceedings, panel members have expressed reservations about the political effectiveness of using the concept of "planetary boundaries": "Planetary boundaries are still an evolving concept that should be used with caution [...] The planetary boundaries question can be divisive as it can be perceived as a tool of the "North" to tell the "South" not to follow the resource intensive and environmentally destructive development pathway that rich countries took themselves... This language is unacceptable to most of the developing countries as they fear that an emphasis on boundaries would place unacceptable brakes on poor countries."
The black line shows the atmospheric carbon dioxide concentration for the period 1880–2008. Red bars show temperatures above and blue bars show temperatures below the average temperature. Year-to-year temperature fluctuations are due to natural processes, such as the effects of El Niño, La Niña, and the eruption of large volcanoes.
Radiative forcing is a measure of the difference between the incoming radiation energy and the outgoing radiation energy acting across the boundary of the earth. Positive radiative forcing results in warming. From the start of the industrial revolution in 1750 to 2005, the increase in atmospheric carbon dioxide has led to a positive radiative forcing, averaging about 1.66 W/m².
The climate scientist Myles Allen thinks setting "a limit on long-term atmospheric carbon dioxide concentrations merely distracts from the much more immediate challenge of limiting warming to 2 °C." He says the concentration of carbon dioxide is not a control variable we can "meaningfully claim to control", and he questions whether keeping carbon dioxide levels below 350 ppm will avoid more than 2 °C of warming.
Adele Morris, policy director, Climate and Energy Economics Project, Brookings Institution, makes a criticism from the economical-political point of view. She puts emphasis in choosing policies that minimize costs and preserve consensus. She favors a system of green-house gas emissions tax, and emissions trading, as ways to prevent global warming. She thinks that too-ambitious objectives, like the boundary limit on CO2, may discourage such actions.
According to the biologist Cristián Samper, a " boundary that expresses the probability of families of species disappearing over time would better reflect our potential impacts on the future of life on Earth."
Since the industrial revolution, the Earth's nitrogen cycle has been disturbed even more than the carbon cycle. "Human activities now convert more nitrogen from the atmosphere into reactive forms than all of the Earth´s terrestrial processes combined. Much of this new reactive nitrogen pollutes waterways and coastal zones, is emitted back to the atmosphere in changed forms, or accumulates in the terrestrial biosphere." Only a small part of the fertilizers applied in agriculture is used by plants. Most of the nitrogen and phosphorus ends up in rivers, lakes and the sea, where excess amounts stress aquatic ecosystems. For example, fertilizer which discharges from rivers into the Gulf of Mexico has damaged shrimp fisheries because of hypoxia.
The biogeochemist William Schlesinger thinks waiting until we near some suggested limit for nitrogen deposition and other pollutions will just permit us to continue to a point where it is too late. He says the boundary suggested for phosphorus is not sustainable, and would exhaust the known phosphorus reserves in less than 200 years.
Peak phosphorus is a concept to describe the point in time at which the maximum global phosphorus production rate is reached. Phosphorus is a scarce finite resource on earth and means of production other than mining are unavailable because of its non-gaseous environmental cycle. According to some researchers, Earth's phosphorus reserves are expected to be completely depleted in 50–100 years and peak phosphorus to be reached in approximately 2030.
Estimated change in sea surface pH from the pre-industrial period (1700s) to the present day (1990s). Δ pH is in standard pH units.
Surface ocean acidity has increased thirty percent since the industrial revolution. About one quarter of the additional carbon dioxide generated by humans is dissolved in the oceans, where it forms carbonic acid. This acidity inhibits the ability of corals, shellfish and plankton to build shells and skeletons. Knock-on effects could have serious consequences for fish stocks. This boundary is clearly interconnected with the climate change boundaries, since the concentration of carbon dioxide in the atmosphere is also the underlying control variable for the ocean acidification boundary.
The ocean chemist Peter Brewer thinks "ocean acidification has impacts other than simple changes in pH, and these may need boundaries too."
Europe land use map. Human land uses include arable farmland (yellow) and pasture (light green)
Across the planet, forests, wetlands and other vegetation types are being converted to agricultural and other land uses, impacting freshwater, carbon and other cycles, and reducing biodiversity.
The environment advisor Steve Bass says research tells us that "the sustainability of land use depends less on percentages and more on other factors. For example, the environmental impact of 15 per cent coverage by intensively farmed cropland in large blocks will be significantly different from that of 15 per cent of land farmed in more sustainable ways, integrated into the landscape. The boundary of 15 per cent land-use change is, in practice, a premature policy guideline that dilutes the authors' overall scientific proposition. Instead, the authors might want to consider a limit on soil degradation or soil loss. This would be a more valid and useful indicator of the state of terrestrial health."
Human pressures on global freshwater systems are having dramatic effects. The freshwater cycle is another boundary significantly affected by climate change. Freshwater resources, such as lakes and aquifers, are usually renewable resources which naturally recharge (the term fossil water is sometimes used to describe aquifers which don't recharge). Overexploitation occurs if a water resource is mined or extracted at a rate that exceeds the recharge rate. Recharge usually comes from area streams, rivers and lakes. Forests enhance the recharge of aquifers in some locales, although generally forests are a major source of aquifer depletion. Depleted aquifers can become polluted with contaminants such as nitrates, or permanently damaged through subsidence or through saline intrusion from the ocean. This turns much of the world's underground water and lakes into finite resources with peak usage debates similar to oil. Though Hubbert's original analysis did not apply to renewable resources, their overexploitation can result in a Hubbert-like peak. A modified Hubbert curve applies to any resource that can be harvested faster than it can be replaced.
The hydrologist David Molden says "a global limit on water consumption is necessary, but the suggested planetary boundary of 4,000 cubic kilometres per year is too generous."
During 21–30 September 2006 the average area of the Antarctic ozone hole was the largest ever observed
The stratospheric ozone layer protectively filters ultraviolet radiation (UV) from the Sun, which would otherwise damage biological systems. The actions taken after the Montreal Protocol appeared to be keeping the planet within a safe boundary. However, in 2011, according to a paper published in Nature, the boundary was unexpectedly pushed in the Arctic; "... the fraction of the Arctic vortex in March with total ozone less than 275 Dobson units (DU) is typically near zero, but reached nearly 45%".
The Nobel laureate in chemistry, Mario Molina, says "five per cent is a reasonable limit for acceptable ozone depletion, but it doesn't represent a tipping point".
Smog over southern China and Vietnam
Aerosol particles in the atmosphere impact the health of humans and influence monsoon and global atmospheric circulation systems. Some aerosols produce clouds which cool the Earth by reflecting sunlight back to space, while others, like soot, produce thin clouds in the upper stratosphere which behave like a greenhouse, warming the Earth. On balance, anthropogenic aerosols probably produce a net negative radiative forcing (cooling influence). Worldwide each year, aerosol particles result in about 800,000 premature deaths. Aerosol loading is sufficiently important to be included among the planetary boundaries, but it is not yet clear whether an appropriate safe threshold measure can be identified.
A Bayesian emulator for persistent organic pollutants has been developed which can potentially be used to quantify the boundaries for chemical pollution. To date, critical exposure levels of polychlorinated biphenyls (PCBs) above which mass mortality events of marine mammals are likely to occur, have been proposed as a chemical pollution planetary boundary.
Interaction among boundaries
A planetary boundary may interact in a manner that changes the safe operating level of other boundaries. Rockström et al. 2009 did not analyze such interactions, but they suggested that many of these interactions will reduce rather than expand the proposed boundary levels.
For example, the land use boundary could shift downward if the freshwater boundary is breached, causing lands to become arid and unavailable for agriculture. At a regional level, water resources may decline in Asia if deforestation continues in the Amazon. Such considerations suggest the need for "extreme caution in approaching or transgressing any individual planetary boundaries."
Another example has to do with coral reefs and marine ecosystems. In 2009, De'Ath, Lough & Fabricius (2009) showed that, since 1990, calcification in the reefs of the Great Barrier that they examined decreased at a rate unprecedented over the last 400 years (14% in less than 20 years). Their evidence suggests that the increasing temperature stress and the declining ocean saturation state of aragonite is making it difficult for reef corals to deposit calcium carbonate. Bellwood & others (2004) explored how multiple stressors, such as increased nutrient loads and fishing pressure, move corals into less desirable ecosystem states. Guinotte & Fabry (2008) showed that ocean acidification will significantly change the distribution and abundance of a whole range of marine life, particularly species "that build skeletons, shells, and tests of biogenic calcium carbonate. "Increasing temperatures, surface UV radiation levels and ocean acidity all stress marine biota, and the combination of these stresses may well cause perturbations in the abundance and diversity of marine biological systems that go well beyond the effects of a single stressor acting alone."
The concept of planetary boundaries challenges the belief that resources are either limitless or infinitely substitutable. It threatens the business-as-usual approach to economic growth. The fact that reference to planetary boundaries was excluded from the [ Rio+20 ] conference statement is a counterintuitive sign that the concept is being taken very seriously and has indeed gained enough traction to be threatening to the status quo. Had planetary boundaries remained in the statement, the most credible interpretation is that they would join a growing list of nice-sounding goals that are included but never achieved in the end. Planetary boundaries will not go away. The intrinsic limits to the amount of resources and environmental services that humanity can extract safely from the Earth System cannot be eliminated by wishful thinking, denial, or omission from official sustainable development conference statements. It is simply the nature of the planet we inhabit.
The Doughnut with indicators to what extent the ecological ceilings are overshot and social foundations are not met yet.
In 2012 Kate Raworth from Oxfam noted the Rockstrom concept does not take human population growth into account. She suggested social boundaries should be incorporated into the planetary boundary structure, such as jobs, education, food, access to water, health services and energy and to accommodate an environmentally safe space compatible with poverty eradication and "rights for all". Within planetary limits and an equitable social foundation lies a doughnut shaped area which is the area where there is a "safe and just space for humanity to thrive in".
An empirical application of the doughnut model by O'Neill et al.  showed that so far across 150 countries not a single country satisfies its citizens' basic needs while maintaining a globally sustainable level of resource use.
Comparisons of national environmental footprints with planetary boundaries
Several studies assessed environmental footprints of nations based on planetary boundaries: for Sweden, Switzerland, the Netherlands,, the European Union  as well as for the world’s most important economies. While the metrics and allocation approaches applied varied, there is a converging outcome that resource use of wealthier nations – if extrapolated to world population – is not compatible with planetary boundaries.
The United Nations secretary general Ban Ki-moon endorsed the concept of planetary boundaries on 16 March 2012, when he presented the key points of the report of his High Level Panel on Global Sustainability to an informal plenary of the UN General Assembly. Ban stated: "The Panel’s vision is to eradicate poverty and reduce inequality, to make growth inclusive and production and consumption more sustainable, while combating climate change and respecting a range of other planetary boundaries." The concept was incorporated into the so-called "zero draft" of the outcome of the United Nations Conference on Sustainable Development to be convened in Rio de Janeiro 20–22 June 2012. However, the use of the concept was subsequently withdrawn from the text of the conference, "partly due to concerns from some poorer countries that its adoption could lead to the sidelining of poverty reduction and economic development. It is also, say observers, because the idea is simply too new to be officially adopted, and needed to be challenged, weathered and chewed over to test its robustness before standing a chance of being internationally accepted at UN negotiations."
The planetary boundary framework was updated in 2015. It was suggested that three of the boundaries (including climate change) might push the Earth system into a new state if crossed; these also strongly influence the remaining boundaries. In the paper, the framework is developed to make it more applicable at the regional scale.
Boundaries related to agriculture and food consumption
Visualization of the planetary boundaries related to agriculture and nutrition 
Human activities related to agriculture and nutrition globally contribute to the transgression of four out of nine planetary boundaries. Surplus nutrient flows (N, P) into aquatic and terrestrial ecosystems are of highest importance, followed by excessive land-system change and biodiversity loss. Whereas in the case of biodiversity loss, P cycle and land-system change, the transgression is in the zone of uncertainty—indicating an increasing risk (yellow circle in the figure), the N boundary related to agriculture is more than 200% transgressed—indicating a high risk (red marked circle in the figure). Here, nutrition includes food processing and trade as well as food consumption (preparation of food in households and gastronomy). Consumption-related environmental impacts are not quantified at the global level for the planetary boundaries of freshwater use, atmospheric aerosol loading (air pollution) and stratospheric ozone depletion. 
Planetary boundaries: A series of commentaries in Nature reports climate change on the planetary boundaries concept set out in the original paper.
^ abcSteffen, W.; Richardson, K.; Rockström, J.; Cornell, S. E.; Fetzer, I.; Bennett, E. M.; Biggs, R.; Carpenter, S. R.; de Vries, W.; de Wit, C. A.; Folke, C.; Gerten, D.; Heinke, J.; Mace, G. M.; Persson, L. M.; Ramanathan, V.; Reyers, B.; Sorlin, S. (2015). "Planetary boundaries: Guiding human development on a changing planet". Science. 347 (6223): 1259855. doi:10.1126/science.1259855. PMID25592418.
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"Boundaries for a Healthy Planet" by Foley J, Daily GC, Howarth R, Vaccari DA, Morris AC, Lambin EF, Doney SC, Peter H. Gleick and Fahey DW. Scientific American, April 2010. Includes opinion essays by invited experts on the planetary boundaries.