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RESEARCH
<br />S Ll S'FA 111114 A 131111 ...11 1"Y
<br />Planetary boundaries: Guiding
<br />human development on a
<br />changing planet
<br />Will Steflegn,' Katherine Richardson, Johan Rc ckstr8m, Sarah. E. Cornell, Ingo Fetzer,
<br />Elena AL Bennett, Reranettc, Baggy;, Stephen R.. Carpenter, Wim de 17nes,
<br />Cyntbia.A. de Wit, Carl. Folke, Dieter Oerte n, Jens; IIehike, Georgina AL Mace,
<br />Linn AL Persso n, Veerabbadrann Ramanatban, Belinda Reyers, Sverker SiMian
<br />INTRODUCTION: There is an urgent need for
<br />a new paradigm that integrates the continued
<br />development of human societies and the main-
<br />tenance of the Earth system (ES) in a resilient
<br />and accommodating state. The planetarybound-
<br />ary (PB) framework contributes to such a
<br />paradigm by providing a science -based analysis
<br />of the risk that human perturbations will de-
<br />stabilize the ES at the planetary scale. Here, the
<br />scientific underpinnings of the PB framework
<br />are updated and strengthened.
<br />RATIONALE: The relatively stable, 11,700 -year-
<br />long Holocene epoch is the only state of the ES
<br />Climate change
<br />Genetic
<br />Biosphere integrity diversib
<br />Functional /
<br />diversity 1/44
<br />Land - system
<br />change
<br />Freshwater use
<br />that we know for certain can support contem-
<br />porary human societies. There is increasing evi-
<br />dence that human activities are affecting ES
<br />functioning to a degree that threatens the re-
<br />silience of the ES —its ability to persist in a
<br />Holocene -like state in the face of increasing
<br />human pressures and shocks. The PB frame-
<br />work is based on critical processes that reg-
<br />ulate ES functioning. By combining improved
<br />scientific understanding of ES functioning with
<br />the precautionary principle, the PB framework
<br />identifies levels of anthropogenic perturbations
<br />below which the risk of destabilization of the
<br />ES is likely to remain low —a "safe operating
<br />7
<br />Novel entities
<br />Stratospheric ozone depletion
<br />Atmospheric aerosol loading
<br />Phosphorus %FI / /% %WIjgllA
<br />Nitrogen Ocean acidification
<br />Biochemical flows
<br />Beyond zone of uncertainty (high risk) Below boundary (safe)
<br />In zone of uncertainty (increasing risk) Boundary not yet quantified
<br />Current status of the control variables for seven of the planetary boundaries. The green zone
<br />is the safe operating space, the yellow represents the zone of uncertainty (increasing risk), and the
<br />red is a high -risk zone. The planetary boundary itself lies at the intersection of the green and yellow
<br />zones. The control variables have been normalized for the zone of uncertainty; the center of the
<br />figure therefore does not represent values of 0 for the control variables. The control variable shown
<br />for climate change is atmospheric CO2 concentration. Processes for which global -level boundaries
<br />cannot yet be quantified are represented by gray wedges; these are atmospheric aerosol loading,
<br />novel entities, and the functional role of biosphere integrity.
<br />space" for global societal development. A zone
<br />of uncertainty for each PB highlights the area
<br />of increasing risk The current level of anthro-
<br />pogenic impact on the ES, and thus the risk to
<br />the stability of the ES, is assessed by compar-
<br />ison with the proposed PB (see the figure).
<br />RESULTS: Three of the PBs (climate change,
<br />stratospheric ozone depletion, and ocean acid-
<br />ification) remain essentially unchanged from
<br />the earlier analysis. Regional -level boundaries
<br />as well as globally aggregated PBs have now
<br />been developed for biosphere integrity (earlier
<br />"biodiversity loss', biogeochemical flows, land -
<br />system change, and freshwater use. At present,
<br />only one regional boundary (south Asian mon-
<br />soon) can be established for atmospheric aerosol
<br />loading. Although we cannot identify a single PB
<br />for novel entities (here de-
<br />fined as new substances,
<br />Pead the hill article, new forms of existing sub-
<br />al III I P: //bujol, stances, and modified life
<br />org /,1.0).,11261 forms that have the po-
<br />tential for unwanted geo-
<br />physical and /or biological
<br />effects), they are included in the PB framework,
<br />given their potential to change the state of the
<br />ES. Two of the PBs— climate change and bio-
<br />sphere integrity —are recognized as "core" PBs
<br />based on their fundamental importance for the
<br />ES. The climate system is a manifestation of the
<br />amount, distribution, and net balance of energy
<br />at Earth's surface; the biosphere regulates ma-
<br />terial and energy flows in the ES and increases
<br />its resilience to abrupt and gradual change.
<br />Anthropogenic perturbation levels of four of
<br />the ES processes /features (climate change, bio-
<br />sphere integrity, biogeochemical flows, and land
<br />system change) exceed the proposed PB (see the
<br />figure).
<br />CONCLUSIONS: PBs are scientifically based
<br />levels of human perturbation of the ES beyond
<br />which ES functioning may be substantially
<br />altered. Transgression of the PBs thus creates
<br />substantial risk of destabilizing the Holocene
<br />state of the ES in which modern societies have
<br />evolved. The PB framework does not dictate
<br />how societies should develop. These are po-
<br />litical decisions that must include considera-
<br />tion of the human dimensions, including equity,
<br />not incorporated in the PB framework Never-
<br />theless, by identifying a safe operating space
<br />for humanity on Earth, the PB framework
<br />can make a valuable contribution to decision -
<br />makers in charting desirable courses for socie-
<br />tal development. Ill
<br />The list of author affiliations is available in the full article online.
<br />*Corresponding author. E -mail: will.steffen @anu.edu.au
<br />Cite this article as W. Steffen et al., Science 347, 1259855
<br />(2015). DOI: 10.1126 /science.1259855
<br />736 13 FEBRUARY 2015 • VOL 347 ISSUE 6223 sciencemag.org SCIENCE
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