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=                        Planetary_boundaries                        =
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                            Introduction
======================================================================
| last1         = Richardson
| first1        = Katherine
| last2         = Steffen
| first2        = Will
| last3         = Lucht
| first3        = Wolfgang
| date          = 2023-09-13
| access-date   =
| title         = Earth beyond six of nine planetary boundaries
| journal       = Science Advances
| volume        = 9
| issue         = 37
| id            = eadh2458
| doi           = 10.1126/sciadv.adh2458
| pmid          = 37703365
| pmc           = 10499318
| bibcode       = 2023SciA....9H2458R
| s2cid         = 261742678

Planetary boundaries are a framework to describe limits to the impacts
of human activities on the Earth system. Beyond these limits, the
environment may not be able to continue to self-regulate. This would
mean the Earth system would leave the period of stability of the
Holocene, in which human society developed.

These nine boundaries are climate change, ocean acidification,
stratospheric ozone depletion, biogeochemical flows in the nitrogen
cycle, excess global freshwater use, land system change, the erosion
of biosphere integrity, chemical pollution, and atmospheric aerosol
loading.

The framework is based on scientific evidence that human actions,
especially those of industrialized societies since the Industrial
Revolution, have become the main driver of global environmental
change. According to the framework, "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-scale to planetary-scale
systems."

The normative component of the framework is that human societies have
been able to thrive under the comparatively stable climatic and
ecological conditions of the Holocene. To the extent that these Earth
system process boundaries have not been crossed, they mark the "safe
zone" for human societies on the planet. Proponents of the planetary
boundary framework propose returning to this environmental and
climatic system; as opposed to human science and technology
deliberately creating a more beneficial climate. The concept doesn't
address how humans have massively altered ecological conditions to
better suit themselves. The climatic and ecological Holocene this
framework considers as a "safe zone" doesn't involve massive
industrial farming. So this framework begs a reassessment of how to
feed modern populations.

The concept has since become influential in the international
community (e.g. United Nations Conference on Sustainable Development),
including governments at all levels, international organizations,
civil society and the scientific community. The framework consists of
nine global change processes. In 2009, according to Rockström and
others, three boundaries were already crossed (biodiversity loss,
climate change and nitrogen cycle), while others were in imminent
danger of being crossed.

In 2015, several of the scientists in the original group published an
update, bringing in new co-authors and new model-based analysis.
According to this update, four of the boundaries were crossed: climate
change, loss of biosphere integrity, land-system change, altered
biogeochemical cycles (phosphorus and nitrogen). The scientists also
changed the name of the boundary "Loss of biodiversity" to "Change in
biosphere integrity" to emphasize that not only the number of species
but also the functioning of the biosphere as a whole is important for
Earth system stability. Similarly, the "Chemical pollution" boundary
was renamed to "Introduction of novel entities", widening the scope to
consider different kinds of human-generated materials that disrupt
Earth system processes.

In 2022, based on the available literature, the introduction of novel
entities was concluded to be the 5th transgressed planetary boundary.
Freshwater change was concluded to be the 6th transgressed planetary
boundary in 2023.


                 Framework overview and principles
======================================================================
The basic idea of the Planetary Boundaries framework is that
maintaining the observed resilience of the Earth system in the
Holocene is a precondition for humanity's pursuit of long-term social
and economic development. The Planetary Boundaries framework
contributes to an understanding of global sustainability because it
brings a planetary scale and a long timeframe into focus.

The framework described nine "planetary life support systems"
essential for maintaining a "desired Holocene state", and attempted to
quantify how far seven of these systems had been pushed already.
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 framework is based on scientific evidence that human actions,
especially those of industrialized societies since the Industrial
Revolution, have become the main driver of global environmental
change. According to the framework, "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-scale to planetary-scale
systems." The framework consists of nine global change processes. In
2009, two boundaries were already crossed, while others were in
imminent danger of being crossed. Later estimates indicated that three
of these boundaries--climate change, biodiversity loss, and the
biogeochemical flow boundary--appear to have been crossed.

The scientists outlined how breaching the boundaries increases the
threat of functional disruption, even collapse, in Earth's biophysical
systems in ways that could be catastrophic for human wellbeing. While
they highlighted scientific uncertainty, they indicated that breaching
boundaries could "trigger feedbacks that may result in crossing
thresholds that drastically reduce the ability to return within safe
levels". 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.

The planetary boundaries framework lays the groundwork for a 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 demarcate, as it were, the
"planetary playing field" for humanity if major human-induced
environmental change on a global scale is to be avoided.


Authors
=========
The authors of this framework was a group of Earth System and
environmental scientists in 2009 led by Johan Rockström from the
Stockholm Resilience Centre and Will Steffen from the Australian
National University. They collaborated with 26 leading academics,
including Nobel laureate Paul Crutzen, Goddard Institute for Space
Studies climate scientist James Hansen, oceanographer Katherine
Richardson, geographer Diana Liverman and the German Chancellor's
chief climate adviser Hans Joachim Schellnhuber.

Most of the contributing scientists were involved in strategy-setting
for the Earth System Science Partnership, the precursor to the
international global change research network Future Earth. The group
wanted to define a "safe operating space for humanity" for the wider
scientific community, as a precondition for sustainable development.


Thresholds and tipping points
===============================
The 2009 study identified nine planetary boundaries and, drawing on
current scientific understanding, the researchers proposed
quantifications for seven of them. These 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 depletion (less than 5% reduction in total
atmospheric O3 from a pre-industrial level of 290 Dobson Units);
# biogeochemical flows in the 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);
# the erosion of biosphere integrity (an annual rate of loss of
biological diversity of < 10 extinctions per million species).
# chemical pollution (introduction of novel entities in the
environment).
For one process in the planetary boundaries framework, the scientists
have not specified a global boundary quantification:

atmospheric aerosol loading;


The quantification of individual planetary boundaries is based on the
observed dynamics of the interacting Earth system processes included
in the framework. The control variables were chosen because together
they provide an effective way to track the human-caused shift away
from Holocene conditions.

For some of Earth's dynamic processes, historic data display clear
thresholds between comparatively stable conditions. For example, past
ice-ages show that during peak glacial conditions, the atmospheric
concentration of CO2 was ~180-200 ppm. In interglacial periods
(including the Holocene), CO2 concentration has fluctuated around 280
ppm. To know what past climate conditions were like with an atmosphere
with over 350 ppm CO2, scientists need to look back about 3 million
years. The paleo record of climatic, ecological and biogeochemical
changes shows that the Earth system has experienced tipping points,
when a very small increment for a control variable (like CO2) triggers
a larger, possibly catastrophic, change in the response variable
(global warming) through feedbacks in the natural Earth System itself.

For several of the processes in the planetary boundaries framework, it
is difficult to locate individual points that mark the threshold shift
away from Holocene-like conditions. This is because the Earth system
is complex and the scientific evidence base is still partial and
fragmented. Instead, the planetary boundaries framework identifies
many Earth system thresholds at multiple scales that will be
influenced by increases in the control variables. Examples include
shifts in monsoon behavior linked to the aerosol loading and
freshwater use planetary boundaries.

Planetary Boundaries (as defined in 2023)
Earth-system process !! Control variable!! Boundary value in 2023  !!
"Current" value  (i.e. for the year provided in the source)     Boundary
now exceeded beyond the 2023 values? (based on "current" value) !!
Preindustrial Holocene base value
rowspan="2" | 1. Climate change          Atmospheric carbon dioxide
concentration (ppm by volume)   350     417     yes     280
Total anthropogenic radiative forcing at top-of-atmosphere (W/m2)
since the start of the industrial revolution (~1750)    1.0     2.91    yes     0
rowspan="2" | 2. Change in biosphere integrity   'Genetic diversity:'
Extinction rate measured as E/MSY (extinctions per million
species-years)  <10 E/MSY but with an aspirational goal of ca. 1
E/MSY (assumed background rate of extinction loss)      >100 E/MSY   yes
1 E/MSY
'Functional diversity:' energy available to ecosystems (NPP) (%
HANPP)  HANPP (in billion tonnes of C year−1) <10% of preindustrial
Holocene NPP, i.e., >90% remaining for supporting biosphere
function        30% HANPP       yes     1.9% (2σ variability of preindustrial Holocene
century-mean NPP)
rowspan="2" | 3. Biogeochemical          Phosphate global: P flow from
freshwater systems into the ocean; regional: P flow from fertilizers
to erodible soils (Tg of P year−1)    'Phosphate global': 11 Tg of P
year−1; 'regional': 6.2 Tg of P year−1 mined and applied to erodible
(agricultural) soils.   'Global': 22 Tg of P year−1; 'regional': 17.5 Tg
of P year−1   yes     0
Nitrogen global: industrial and intentional fixation of N (Tg of N
year−1)       62      190     yes     0
4. Ocean acidification   Global mean saturation state of calcium
carbonate in surface seawater (omega units)     2.75    2.8     no      3.44
5. Land use      Part of forests rested intact (percent)        75 from all
forests including 85 from Boreal forest, 50 from Temperate forests and
85 from Tropical forests        'Global': 60    yes     100
rowspan="2" | 6. Freshwater change       Blue water: human induced
disturbance of blue water flow  Upper limit (95th percentile) of global
land area with deviations greater than during preindustrial, Blue
water: 10.2%    18.2%   yes     9.4%
Green water: human induced disturbance of water available to plants
(% land area with deviations from preindustrial variability)    11.1%
15.8%   yes     9.8%
7. Ozone depletion       Stratospheric ozone concentration (Dobson units)
276     284.6   no      290
8. Atmospheric aerosols          Interhemispheric difference in AOD (Aerosol
Optical Depth)  0.1 (mean annual interhemispheric difference)   0.076
no      0.03
9. Novel entities        Percentage of synthetic chemicals released to the
environment without adequate safety testing     0       Transgressed    yes     0
colspan="6"


"Safe operating spaces"
=========================
The planetary boundaries framework proposes a range of values for its
control variables. This range is supposed to span the threshold
between a 'safe operating space' where Holocene-like dynamics can be
maintained and a highly uncertain, poorly predictable world where
Earth system changes likely increase risks to societies. The
'boundary' is defined as the lower end of that range. If the
boundaries are persistently crossed, the world goes further into a
danger zone.

It is difficult to restore a 'safe operating space' for humanity that
is described by the planetary boundary concept. Even if past
biophysical changes could be mitigated, the predominant paradigms of
social and economic development appear largely indifferent to the
looming possibilities of large scale environmental disasters triggered
by human actions. Legal boundaries can help keep human activities in
check, but are only as effective as the political will to make and
enforce them.


Interaction among boundaries
==============================
Understanding the Earth system is fundamentally about understanding
interactions among environmental change processes. The planetary
boundaries are defined with reference to dynamic conditions of the
Earth system, but scientific discussions about how different planetary
boundaries relate to each other are often philosophically and
analytically muddled. Clearer definitions of the basic concepts and
terms might help give clarity.

There are many many interactions among the processes in the planetary
boundaries framework. While these interactions can create both
stabilizing and destabilizing feedbacks in the Earth system, the
authors suggested that a transgressed planetary boundary will reduce
the safe operating space for other processes in the framework rather
than expand it from the proposed boundary levels. They give the
example that 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. That way of
framing the interactions shifts from the framework's biophysical
definition of boundaries based on Holocene-like conditions to an
anthropocentric definition (demand for agricultural land). Despite
this conceptual slippage, considerations of known Earth system
interactions across scales 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, researchers 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. Multiple stressors, such
as increased nutrient loads and fishing pressure, moves corals into
less desirable ecosystem states. 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."


Proposed new or expanded boundaries since 2012
================================================
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".

In 2015, a second paper was published in 'Science' to update the
Planetary Boundaries concept. The update concluded four boundaries had
now been transgressed: climate, biodiversity, land use and
biogeochemical cycles. The 2015 paper emphasized interactions of the
nine boundaries and identified climate change and loss of biodiversity
integrity as 'core boundaries' of central importance to the framework
because the interactions of climate and the biosphere are what
scientifically defines Earth system conditions.

In 2017, some authors argued that marine systems are underrepresented
in the framework. Their proposed remedy was to include the seabed as a
component of the earth surface change boundary. They also wrote that
the framework should account for "changes in vertical mixing and ocean
circulation patterns".

Subsequent work on planetary boundaries begins to relate these
thresholds at the regional scale.


Climate change
================
A 2018 study calls into question the adequacy of efforts to limit
warming to 2 °C above pre-industrial temperatures, as set out in the
Paris Agreement. The scientists raise the possibility that even if
greenhouse gas emissions are substantially reduced to limit warming to
2 °C, that might exceed 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 for people, raise sea levels by up to 60 m, and
raise temperatures by 4 - to levels that are higher than any
interglacial period in the past 1.2 million years.


Change in biosphere integrity
===============================
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."
The biodiversity boundary has also been criticized for framing
biodiversity solely in terms of the extinction rate. The global
extinction rate has been highly variable over the Earth's history, and
thus using it as the only biodiversity variable can be of limited
usefulness.


Nitrogen and phosphorus
=========================
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.

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."

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 by approximately 2030. However, recent evidence shows
that if phosphorus applications to soil are matched to the agronomic
optimum for crop yield, it would take >500 years to exhaust
currently econimically viable phosphorus reserves.


Ocean acidification
=====================
Surface ocean acidity 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."


Land-system change
====================
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. In the
year 2015 the boundary was defined as 75% of forests rested intact,
including 85% of boreal forests, 50% of temperate forests and 85% of
tropical forests. The boundary is crossed because only 62% of forests
rested intact as of the year 2015.

The boundary for land use has been criticized as follows: "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."


Freshwater
============
The freshwater cycle is another boundary significantly affected by
climate change. Overexploitation of freshwater occurs if a water
resource is mined or extracted at a rate that exceeds the recharge
rate. Water pollution and saltwater intrusion can also turn much of
the world's underground water and lakes into finite resources with
"peak water" usage debates similar to oil.

The hydrologist David Molden stated in 2009 that planetary boundaries
are a welcome new approach in the "limits to growth" debate but said
"a global limit on water consumption is necessary, but the suggested
planetary boundary of 4,000 cubic kilometres per year is too
generous."


Green and blue water
======================
A study concludes that the 'Freshwater use' boundary should be renamed
to the 'Freshwater change', composed of "green" and "blue" water
components. When measuring and projecting water scarcity in
agriculture for climate change scenarios, both "green water" and "blue
water" are of relevance.

In April 2022, scientists proposed and preliminarily evaluated 'green
water' in the water cycle as a likely transgressed planetary boundary,
as measured by root-zone soil moisture deviation from Holocene
variability.


Ozone depletion
=================
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.

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".


Atmospheric aerosols
======================
Worldwide each year, aerosol particles result in about 800,000
premature deaths from air pollution. 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.


Novel entities (chemical pollution)
=====================================
Some chemicals, such as persistent organic pollutants, heavy metals
and radionuclides, have potentially irreversible additive and synergic
effects on biological organisms, reducing fertility and resulting in
permanent genetic damage. Sublethal uptakes are drastically reducing
marine bird and mammal populations. This boundary seems important,
although it is hard to quantify. In 2019, it was suggested that novel
entities could include genetically modified organisms, pesticides and
even artificial intelligence.

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.

There are at least 350,000 artificial chemicals in the world. They are
coming from "plastics, pesticides, industrial chemicals, chemicals in
consumer products, antibiotics and other pharmaceuticals". They have
mostly "negative effects on planetary health". Their production
increased 50 times since 1950 and is expected to increase 3 times more
by 2050. Plastics alone contain more than 10,000 chemicals and create
large problems. The researchers are calling for limit on chemical
production and shift to circular economy, meaning to products that can
be reused and recycled.

In January 2022 a group of scientists concluded that this planetary
boundary is already exceeded, which puts in risk the stability of the
Earth system. They integrated the literature information on how
production and release of a number of novel entities, including
plastics and hazardous chemicals, have rapidly increased in the last
decades with significant impact on the planetary processes.

In August 2022, scientists concluded that the (overall transgressed)
boundary is a placeholder for multiple different boundaries for NEs
that may emerge, reporting that PFAS pollution is one such new
boundary. They show that levels of these so-called "forever chemicals"
in rainwater are ubiquitously, and often greatly, above guideline safe
levels worldwide. There are some moves to restrict and replace their
use.


Planetary integrity
=====================
'Planetary integrity' is also called 'earth's life-support systems' or
'ecological integrity'. Scholars have pointed out that planetary
integrity "needs to be maintained for long-term sustainability". The
term 'integrity' refers to ecological health in this context. The
concept of planetary integrity is interlinked within the concept of
planetary boundaries.

An 'Expert Panel on Ecological Integrity' in 1998 has defined
'ecological integrity' as follows: "Ecosystems have integrity when
they have their native components (plants, animals and other
organisms) and processes (such as growth and reproduction) intact."

There are many negative human impacts on the environment that are
causing a reduction in planetary integrity. For example, the current
biodiversity loss is threatening ecological integrity on a global
scale. The Sustainable Development Goals might be able to act as a
steering mechanism to address the current loss of planetary integrity.


The "Limits to Growth" (1972) and Gaia theory
===============================================
The idea that there are limits to the burden placed upon our planet by
human activities has been around for a long time. The Planetary
Boundaries framework acknowledges the influence of the 1972 study,
'The Limits to Growth', that presented a model in which exponential
growth in world population, industrialization, pollution, food
production, and resources depletion outstrip the ability of technology
to increase resources availability. Subsequently, the report was
widely dismissed, particularly by economists and business people, 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". 'The Limits
to Growth' has been widely discussed, both by critics of the modelling
approach and its conclusions and by analysts who argue that the
insight that societies do not live in an unlimited world and that
historical data since the 1970s support the report's findings. The
'Limits to Growth' approach explores how the socio-technical dynamics
of the world economy may limit humanity's opportunities and introduce
risks of collapse. In contrast, the Planetary Boundaries framework
focuses on the biophysical dynamics of the Earth system.

'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."

Another key idea influencing the Planetary Boundaries framework is the
Gaia theory or hypothesis. In the 1970s, James Lovelock and
microbiologist Lynn Margulis presented the idea 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 Lovelock's book 'The Revenge of Gaia', he suggests that
the destruction of rainforests and biodiversity, compounded with
global warming resulting from the increase of greenhouse gases made by
humans, could shift feedbacks in the Earth system away from a
self-regulating balance to a positive (intensifying) feedback loop.


Anthropocene
==============
Scientists have affirmed that 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
resilient and recover from that change, potentially ultimately
threatening planetary habitability. The previous geological epoch, the
Holocene began about 10,000 years ago. It is the current interglacial
period, and was a relatively stable environment of the Earth. There
have been natural environmental fluctuations during the Holocene, but
the key atmospheric and biogeochemical parameters have remained within
relatively narrow bounds. This stability has allowed societies to
thrive worldwide, developing agriculture, large-scale settlements and
complex networks of trade.

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."

Various biophysical processes that are important in maintaining the
resilience of the Earth system are also undergoing large and rapid
change because of human actions. For example, since the advent of the
Anthropocene, the rate at which species are going extinct 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 perturbation of Earth system processes by human
activities raises the possibility that further pressure could be
destabilizing, leading to non-linear, abrupt, large-scale or
irreversible environmental change responses by the Earth system within
continental- to planetary-scale systems.


                        Reception and debate
======================================================================
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.

Development studies scholars have been critical of aspects of the
framework and constraints that its adoption could place on the Global
South. Proposals to conserve a certain proportion of Earth's remaining
forests can be seen as rewarding the countries such as those in Europe
that have already economically benefitted from exhausting their
forests and converting land for agriculture. In contrast, countries
that have yet to industrialize are asked to make sacrifices for global
environmental damage they may have had little role in creating.

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."

In a global empirical study, researchers investigated how students of
environmental and sustainability studies in 35 countries assessed the
planetary boundaries. It was found that there are substantial global
differences in the perception of planetary boundaries.


National environmental footprints
===================================
Several studies have assessed environmental footprints of nations
based on planetary boundaries: for Portugal, Sweden, Switzerland, the
Netherlands, the European Union, India, many of Belt and Road
Initiative countries  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.


Boundaries related to agriculture and food consumption
========================================================
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.


Individual and collective allowances
======================================
Approaches based on a general framework of ecological limits include
(transferable) personal carbon allowances and "legislated" national
greenhouse gas emissions limits. Consumers would have freedom in their
(informed) choice within (the collective) boundaries.


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."

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."

However, the concept is routinely used in the proceedings of the
United Nations, and in the 'UN Daily News'. For example, the United
Nations Environment Programme (UNEP) Executive Director Achim Steiner
states that the challenge of agriculture is to "feed a growing global
population without pushing humanity's footprint beyond planetary
boundaries." The UNEP Yearbook 2010 also repeated Rockström's message,
conceptually linking it with ecosystem management and environmental
governance indicators.

In their 2012 report 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"".


European Commission
=====================
The planetary boundaries concept is also used in proceedings by the
European Commission, and was referred to in the European Environment
Agency synthesis report 'The European environment - state and outlook
2010'.


                              See also
======================================================================
* Ecological footprint
* Global catastrophic risk
* Global change
* Holocene extinction
* Human impact on the nitrogen cycle
* Human impacts on the environment
* Planetary health
* Planetary management
*Sustainability
*Triple Planetary Crisis


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*   The web page inverts the book title.
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                           External links
======================================================================
*
[https://www.stockholmresilience.org/research/planetary-boundaries/planetary-boundaries-data.html
Figures and data] for the updated Planetary Boundaries can be found at
the Stockholm Resilience Centre website.
*
[http://www.nature.com/news/specials/planetaryboundaries/index.html#feature
Planetary Boundaries: Specials] 'Nature,' 24 September 2009.
*
[https://www.ted.com/talks/johan_rockstrom_let_the_environment_guide_our_development
Johan Rockstrom: Let the environment guide our development] TED video,
July 2010.
[http://initforthegold.blogspot.com/2010/09/rockstrom-on-planetary-boundaries.html
Transcript html]
*


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