= a specific point related to a global-scale environmental process beyond which humanity should not go; nine processes and systems regulate the stability and resilience of the earth system
"The planetary boundaries concept, first published in 2009, identifies nine global priorities relating to human-induced changes to the environment. The science shows that these nine processes and systems regulate the stability and resilience of the earth system – the interactions of land, ocean, atmosphere and life that together provide conditions upon which our societies depend.
Nine planetary boundaries:
- Climate change
- Change in biosphere integrity (biodiversity loss and species extinction)
- Stratospheric ozone depletion
- Ocean acidification
- Biogeochemical flows (phosphorus and nitrogen cycles)
- Land-system change (for example deforestation)
- Freshwater use
- Atmospheric aerosol loading (microscopic particles in the atmosphere that affect climate and living organisms)
- Introduction of novel entities (e.g. organic pollutants, radioactive materials, nanomaterials, and micro-plastics)."
1. Will Steffen, Robert Constanza et al.:
"How do we begin to identify what aspects of our planet need boundaries and what those boundaries are? The concept of planetary boundaries, while building on earlier efforts, takes a rather different approach. It does not focus so directly on the human enterprise, as do most of these earlier approaches, but rather emphasizes the Earth as a complex system. Here we identify nine areas that are most in need of set planetary boundaries: climate change; biodiversity loss; excess nitrogen and phosphorus production, which pollutes our soils and waters; stratospheric ozone depletion; ocean acidification; global consumption of freshwater; change in land use for agriculture; air pollution; and chemical pollution.
What do we mean by “boundary”? This refers to a specific point related to a global-scale environmental process beyond which humanity should not go. The position of the boundary is a normative judgment, informed by science but largely based on human perceptions of risk. This doesn’t mean that any change in the Earth system is dangerous. Our planet can undergo abrupt changes naturally. An example is the sudden switch in North Atlantic ocean circulation when a critical level of freshwater input is reached. But these thresholds and abrupt changes are intrinsic features of the Earth system and cannot be eliminated or modified by human actions, such as the development of new technologies. We have to learn to live with thresholds and respect them. An abrupt change is a hardwired feature of the Earth system independent of human existence, while violation of a boundary is a subjective judgment by humanity about how close we wish to approach dangerous or potentially catastrophic thresholds in our own life-support system." (http://www.stwr.org/climate-change-environment/how-defining-planetary-boundaries-can-transform-our-approach-to-growth.html)
Source: "This article is based on the papers “A safe operating space for humanity,” published in Nature, and “Planetary boundaries: Exploring the safe operating space for humanity,”  published in Ecology and Society. See these papers for a complete description of the planetary boundaries."
2. From the Wikipedia:
"Planetary boundaries is the central concept in an Earth system framework proposed 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. In 2009, the group proposed a framework of “planetary boundaries” designed 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. This framework is based on scientific research that indicates that since the Industrial Revolution, human actions have gradually become the main driver of global environmental change. The scientists assert that once human activity has passed certain thresholds or tipping points, defined as “planetary boundaries”, there is a risk of “irreversible and abrupt environmental change”. The scientists identified nine Earth system processes which have boundaries that, to the extent that they are not crossed, mark the safe zone for the planet. However, because of human activities some of these dangerous boundaries have already been crossed, while others are in imminent danger of being crossed.
Rockström and Steffen 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. The group identified nine "planetary life support systems" essential for human survival, and attempted to quantify just how far seven of these systems have been pushed already. They then estimated how much further we can go before our own survival is threatened; beyond these boundaries there is a risk of "irreversible and abrupt environmental change" which could make Earth less habitable. Estimates indicate that three of these boundaries—climate change, biodiversity loss, and the biogeochemical flow boundary—appears to have been crossed. The boundaries are "rough, first estimates only, surrounded by large uncertainties and knowledge gaps" that interact in ways that are complex and not well understood. Boundaries can help identify where there is room and define a "safe space for human development", which is an improvement on approaches which aim at just minimizing human impacts on the planet.
The group published their full findings in a 2009 report and presented it to the General Assembly of the Club of Rome in Amsterdam. An edited summary of the report was subsequently published as the featured article in a special edition of Nature. Nature also published critical commentary from leading academics they invited to comment on each of the seven planetary boundaries which had been quantified, including comments from Nobel laureate Mario J. Molina and biologist Cristián Samper." (https://en.wikipedia.org/wiki/Planetary_boundaries)
Climate change, biodiversity loss, and phosphorus and nitrogen production are just three areas in which boundaries can be determined and measured, and we will use these as examples.
Human-provoked climate change is no longer disputed. Scientists can measure climate change by studying the levels of CO2 in our atmosphere. Our proposed climate boundary is that human changes to atmospheric CO2 should not drive its concentration beyond 350 parts per million by volume, and that radiative forcing—the change in the energy balance at the Earth’s surface—should not exceed 1 watt per square meter above preindustrial levels. Transgressing these boundaries could lead to the melting of ice sheets, rising sea level, abrupt shifts in forest and agricultural land, and increasing intensity and frequency of extreme events like floods, wildfires, and heat waves.
A second example is biodiversity loss, which does occur naturally and would continue to some degree without human interference. However, the rate of animal extinction has skyrocketed in the postindustrial age. Compared with fossil records, today the rate of extinction per species is 100–1,000 times more than what could be considered natural. Human activities are to blame: urban and agricultural development, sprawl, increases in wildfires that destroy habitat, introduction of new species into environments, and the exploitation of land for human consumption—such as the destruction of the rainforests. We believe another 30 percent of wildlife will come under the threat of extinction this century if change is not made. The dangers of biodiversity loss go beyond nostalgia for certain animals: entire ecosystems rely on certain threatened species.
Setting a planetary boundary for biodiversity is difficult because there is so little known about the way in which species are interwoven and how they connect to the broader environment. However, we propose beginning by using the extinction rate as a flawed but acceptable indicator. Our suggested planetary boundary is that of ten times the background rate of extinction. More research may change this boundary.
In our third example, we propose that no more than 11 million tonnes of phosphorous should be allowed to flow into the ocean each year—which is ten times the natural background state. Excessive production of phosphorus, along with nitrogen, is a by-product of our agricultural system. Excessive phosphorous and nitrogen production pollutes waterways and coastal areas and adds harmful gases to the atmosphere. Current levels already exceed critical thresholds for many estuaries and freshwater sites, and so further research may reduce the current phosphorus and nitrogen boundaries.
We propose that a boundary be set for each of the nine areas and that it be respected globally, in order for humans to continue along a healthy, productive path for an indefinite amount of time. It is important to acknowledge that we don’t know precisely where the threshold might lie along the control variable (i.e., a variable—sometimes a human intervention—that can influence whether or not a threshold is crossed) or how much change in a slow process will undermine resilience at larger scales. Thus, we need to define a zone within which we are reasonably sure the threshold lies or beyond which we are reasonably sure that a significant degree of resilience will be lost.
Staying within the “planetary playing field” does not assure that humanity will thrive, or even survive, but straying outside the playing field will make it very difficult for humanity to thrive under any circumstances. Implementing the concept of planetary boundaries presents huge challenges for global governance and institutions." (http://www.stwr.org/climate-change-environment/how-defining-planetary-boundaries-can-transform-our-approach-to-growth.html)
"Four of nine planetary boundaries have now been crossed as a result of human activity, says an international team of 18 researchers that includes Scripps Institution of Oceanography at UC San Diego Distinguished Climate and Atmospheric Scientist Veerabhadran Ramanathan.
The team reports in the Jan. 16 issue of the journal Science that in the planetary boundary categories of climate change, biosphere integrity, land-system change, and altered biogeochemical cycles, thresholds have been crossed that fundamentally change the functions of nature.
The scientists say that two of these, climate change and biosphere integrity, are “core boundaries.” Significantly altering either of these “core boundaries” would “drive the earth system into a new state.”
“This is one of the first attempts to undertake an integrated assessment of all the major environmental threats to sustainability of humanity and the ecosystem,” said Ramanathan. “The implications are sobering.”
Lead author Will Steffen from the Stockholm Resilience Centre at Stockholm University and the Australian National University, Canberra, said: “Transgressing a boundary increases the risk that human activities could inadvertently drive the earth system into a much less hospitable state, damaging efforts to reduce poverty and leading to a deterioration of human well-being in many parts of the world, including wealthy countries. In this new analysis, we have improved our quantification of where these risks lie.” (https://scripps.ucsd.edu/news/earth-has-crossed-several-planetary-boundaries-thresholds-human-induced-environmental-changes)
Critical Features of the Planetary Boundaries Concept
Will Steffen, Johan Rockström and Robert Costanza:
"Several features of the planetary boundaries conceptual framework are critical to understanding how the approach works.
First, planetary boundaries are explicitly designed for the global scale and are aimed at keeping the Earth within safe ranges that existed prior to the Industrial Revolution. Although some Earth-system processes, such as ocean acidification, are intrinsically global in scale, others become global only when they aggregate from much smaller scales.
In no way does this mean that local or regional environmental issues, which have largely been the focus of policy and management for decades, have become less important. Efforts to reduce pollution and limit and reverse ecosystem degradation at local and regional scales continue to be very important and in fact have become even more important because of their larger-scale implications. However, we must now also focus on the global scale explicitly—in addition to and not at the expense of the many environmental issues we still need to solve at smaller scales. A global solution to the sustainability challenge is thus a prerequisite for living sustainably at local and regional scales.
Second, there is much interaction among the planet’s features that lies at the heart of the planetary boundaries approach. This is not at all surprising given that the Earth behaves as a single, complex system at the global scale, but it does complicate the formulation and implementation of planetary boundaries. There are cascading impacts, in which transgressing one boundary can have implications for other boundaries. For example, converting the Amazon rainforest to a grassland or savanna could influence atmospheric circulation globally and ultimately affect water resources in East Asia through changes in rainfall.
Even small changes can have a synergistic effect when linked to other small changes. For example, conversion of forest to cropland, increased use of nitrogen and phosphorus fertilizers, and increased extraction of freshwater for irrigation could all act together to reduce biodiversity more than if each of these variables acted independently. Many changes feed back into each other. The processes involving ocean acidity and atmospheric CO2 concentration are an example of a reinforcing feedback loop. An increase in ocean acidity reduces the strength of the “biological pump” that removes carbon from the atmosphere, which in turn increases the atmospheric CO2 concentration, which increases the physical uptake of CO2 by the ocean, which further increases acidity, and so on.
Finally, the planetary boundaries approach doesn’t say anything explicit about resource use, affluence, or human population size. These are part of the trade-offs that allow humanity to continue to pursue increased well-being. The boundaries simply define the regions of global environment space that, if human activities push the Earth system into that space, would lead to unacceptably deleterious consequences for humanity as a whole.
Because the planetary boundaries approach says nothing about the distribution of affluence and technologies among the human population, a “fortress world,” in which there are huge differences in the distribution of wealth, and a much more egalitarian world, with more equitable socioeconomic systems, could equally well satisfy the boundary conditions. These two socioeconomic states, however, would deliver vastly different outcomes for human well-being. Thus, remaining within the planetary boundaries is a necessary—but not sufficient—condition for a bright future for humanity." (http://www.stwr.org/climate-change-environment/how-defining-planetary-boundaries-can-transform-our-approach-to-growth.html)
- summary of common objections: http://makewealthhistory.org/2013/08/14/planetary-boundaries-some-common-objections/?