Planetary boundaries

Planetary boundaries is a concept involving Earth system processes which contain environmental boundaries, proposed in 2009 by a group of Earth system and environmental scientists led by Johan Rockström from the Stockholm Resilience Centre and Will Steffen from the Australian National University. The group wanted to define a “safe operating space for humanity” for the international community, including governments at all levels, international organizations, civil society, the scientific community and the private sector, as a precondition for sustainable development. The framework is based on scientific evidence that human actions since the Industrial Revolution have become the main driver of global environmental change.

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.

History of framework
In 2009, a group of Earth system and environmental scientists led by Johan Rockström from the Stockholm Resilience Centre and Will Steffen from the Australian National University collaborated with 26 leading academics, including Nobel laureate Paul Crutzen, Goddard Institute for Space Studies climate scientist James Hansen and the German Chancellor’s chief climate adviser Hans Joachim Schellnhuber and identified nine “planetary life support systems” essential for human survival, attempting to quantify how far seven of these systems had been pushed already. They estimated how much further humans can go before planetary habitability is threatened. Estimates indicated that three of these boundaries—climate change, biodiversity loss, and the biogeochemical flow boundary—appear to have been crossed. The boundaries were “rough, first estimates only, surrounded by large uncertainties and knowledge gaps” which interact in complex ways that are not yet well understood. Boundaries were defined to help define a “safe space for human development”, which was an improvement on approaches aiming at minimizing human impacts on the planet. The 2009 report was presented to the General Assembly of the Club of Rome in Amsterdam. An edited summary of the report was published as the featured article in a special 2009 edition of Nature. alongside invited critical commentary from leading academics like Nobel laureate Mario J. Molina and biologist Cristián Samper.

In 2015, a second paper was published in Science to update the Planetary Boundaries concept and findings were presented at the World Economic Forum in Davos, January 2015.

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 idea
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.”

Our Common Future was published in 1987 by United Nations’ World Commission on Environment and Development. It tried to recapture the spirit of the Stockholm Conference. Its aim was to interlock the concepts of development and environment for future political discussions. It introduced the famous definition for sustainable development:

“Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

— Brundtland Report 1987

Of a different kind is the approach made by James Lovelock. In the 1970s he and microbiologist Lynn 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.

From Holocene to Anthropocene
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 change to the Earth system. There have been well publicized scientific warnings about risks in the areas of climate change and stratospheric ozone. However, other biophysical processes are also important. 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’s biophysical systems from human activities raises concerns that further pressure could be destabilizing, and precipitate sudden or irreversible changes to the environment. 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 address the issue, 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.

Nine boundaries

Thresholds and boundaries

The threshold, or climatological tipping point, is the value at which a very small increment for the control variable (like CO2) produces a large, possibly catastrophic, change in the response variable (global warming).

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 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.

Planetary Boundaries
Earth-system process Control variable Boundary
Boundary crossed Preindustrial
1. Climate change Atmospheric carbon dioxide concentration (ppm by volume)

350 400 yes 280
Alternatively: Increase in radiative forcing (W/m2) since the start of the industrial revolution (~1750) 1.0 1.5 yes 0
2. Biodiversity loss Extinction rate (number of species per million per year) 10 > 100 yes 0.1–1
3. Biogeochemical (a) anthropogenic nitrogen removed from the atmosphere (millions of tonnes per year) 35 121 yes 0
(b) anthropogenic phosphorus going into the oceans (millions of tonnes per year) 11 8.5–9.5 no −1
4. Ocean acidification Global mean saturation state of aragonite in surface seawater (omega units) 2.75 2.90 no 3.44
5. Land use Land surface converted to cropland (percent) 15 11.7 no low
6. Freshwater Global human consumption of water (km3/yr) 4000 2600 no 415
7. Ozone depletion Stratospheric ozone concentration (Dobson units) 276 283 no 290
8. Atmospheric aerosols Overall particulate concentration in the atmosphere, on a regional basis not yet quantified
9. Chemical pollution Concentration of toxic substances, plastics, endocrine disruptors, heavy metals, and radioactive contamination into the environment not yet quantified

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); biogeochemical nitrogen (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 boundary level are chemical pollution and atmospheric aerosol loading.

Environmental Footprints and Planetary Load Limits
Various studies examined the ecological footprint of Sweden, Switzerland, and the world’s major economies, based on the limits of the planet’s load capacity. Different methodological approaches were used. A common result is that the resource consumption of wealthy countries – extrapolated to the world population – is incompatible with several limits of the planet’s capacity. For Switzerland, for example, this applies to the greenhouse gas, the biodiversity, and the eutrophication footprint (by nitrogen).

Planetary limits of agriculture and nutrition
The field of agriculture and nutrition is globally responsible for exceeding four of the total of nine load limits considered. Excessive nutrient inputs into terrestrial and aquatic ecosystems are of paramount importance to the nitrogen and phosphorus cycles, followed by excessive land-use change and biodiversity loss caused by agriculture and nutrition.

Description of the Concept of the Planetary Guardrails
The concept of the planetary guard rails of the German Advisory Council on Global Change (WBGU) is comparable to the Planetary Boundaries.

dimension measurand
Limit climate change to 2 ° C Global CO 2 emissions from fossil sources are expected to be completely phased out by about 2070.
Limit ocean acidification to 0.2 pH units Global CO 2 emissions from fossil sources are expected to be completely phased out by about 2070. (ditto climate change)
Stop loss of biodiversity and ecosystem services The immediate anthropogenic drivers of biodiversity loss are expected to be halted by 2050 at the latest.
Stop land and soil degradation The net land degradation is to be stopped by 2030 worldwide and in all countries.
Limit exposure to long-lived anthropogenic pollutants
mercury The substitutable use as well as the anthropogenic mercury emissions should be stopped by 2050.
plastic The release of plastic waste into the environment should be stopped worldwide by 2050.
Cleavable material The production of nuclear fuel for use in nuclear weapons and for use in civil nuclear reactors is to be stopped by 2070.
Stop loss of phosphorus The release of non-recoverable phosphorus should be stopped by 2050, so that its circulation can be achieved worldwide.

The ozone hole is no longer considered Planetary Guardrails. The same is true in Die Zeit: “We assume… that the ozone layer will gradually recover since the ban on ozone-depleting substances.”

Fresh water consumption and aerosols are also not listed as planetary guard rails in the concept of the WBGU.

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.”

Subsequent developments

The doughnut
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”.

Tenth boundary
In 2012, Steven Running suggested a tenth boundary, the annual net global primary production of all terrestrial plants, as an easily determinable measure integrating many variables that will give “a clear signal about the health of ecosystems”.

Not yet endorsed by United Nations
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.

Agricultural and nutritional impacts
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, the N boundary related to agriculture is more than 200% transgressed—indicating a high risk.

Source from Wikipedia