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RESEARCH
<br />S 1.1 S'Y'A 11 1114 A 13 11 11 II "i "'Y
<br />Planetary boundaries: Guiding
<br />human development on a
<br />changing planet
<br />Will Steffen,' 2* Katherine Ricban°tlso n,`� Jobagn Rockstriim,' Sarab E. Cornell,'
<br />� ' � Ingo Fetzer,' Elena M. Bennett Re ette Baggy, Steppe R. Carpenter,
<br />Wim de Vnes,71" C',yantlaaa.A. de Wit," C",arl. Folke, " "' Dieter Gertean," Deny; Heinnke," °12,13
<br />, ' �ecaaslalaan Iamanatlan,'� °'7 GeorginaM. Mace ' Linn M. Persso ,°
<br />Belinda Reyers,11"' Sverker Siar]hi "'
<br />The planetary boundaries framework defines a safe operating space for humanity based
<br />on the intrinsic biophysical processes that regulate the stability of the Earth system.
<br />Here, we revise and update the planetary boundary framework, with a focus on the
<br />underpinning biophysical science, based on targeted input from expert research
<br />communities and on more general scientific advances over the past 5 years. Several of the
<br />boundaries now have a two -tier approach, reflecting the importance of cross -scale
<br />interactions and the regional -level heterogeneity of the processes that underpin the
<br />boundaries. Two core boundaries — climate change and biosphere integrity —have been
<br />identified, each of which has the potential on its own to drive the Earth system into a new
<br />state should they be substantially and persistently transgressed.
<br />he planetary boundary (PB) approach (1, 2)
<br />aims to define a safe operating space for
<br />human societies to develop and thrive, based
<br />on our evolving understanding of the func-
<br />tioning and resilience of the Earth system.
<br />Since its introduction, the framework has been
<br />subject to scientific scrutiny [e.g., (3 -7)] and has
<br />attracted considerable interest and discussions
<br />within the policy, governance, and business sec-
<br />tors as an approach to inform efforts toward glob-
<br />al sustainability (3 -10).
<br />In this analysis, we further develop the basic
<br />PB framework by (i) introducing a two -tier ap-
<br />proach for several of the boundaries to account
<br />for regional -level heterogeneity; (ii) updating the
<br />quantification of most of the PBs; (iii) identifying
<br />two core boundaries; and (iv) proposing a regional -
<br />level quantitative boundary for one of the two
<br />that were not quantified earlier (1).
<br />The basic framework: Defining
<br />a safe operating space
<br />Throughout history, humanity has faced environ-
<br />mental constraints at local and regional levels,
<br />with some societies dealing with these challenges
<br />more effectively than others (11,12). More recent-
<br />ly, early industrial societies often used local water-
<br />ways and airsheds as dumping grounds for their
<br />waste and effluent from industrial processes. This
<br />eroded local and regional environmental quality
<br />and stability, threatening to undermine the pro-
<br />gress made through industrialization by damag-
<br />ing human health and degrading ecosystems.
<br />Eventually, this led to the introduction of local
<br />or regional boundaries or constraints on what
<br />could be emitted to and extracted from the en-
<br />vironment (e.g., chemicals that pollute airsheds
<br />or waterways) and on how much the environment
<br />could be changed by direct human modification
<br />(land- use /cover change in natural ecosystems)
<br />(13). The regulation of some human impacts on
<br />the environment —for example, the introduction
<br />of chemical contaminants —is often framed in
<br />the context of "safe limits" (14).
<br />These issues remain, but in addition we now
<br />face constraints at the planetary level, where the
<br />magnitude of the challenge is vastly different.
<br />The human enterprise has grown so dramatically
<br />since the mid -20th century (15) that the relatively
<br />stable, 11,700 -year -long Holocene epoch, the only
<br />state of the planet that we know for certain can
<br />support contemporary human societies, is now
<br />being destabilized (figs. S1 and S2) (16 -13). In
<br />fact, a new geological epoch, the Anthropocene,
<br />has been proposed (19).
<br />The precautionary principle suggests that hu-
<br />man societies would be unwise to drive the Earth
<br />system substantially away from a Holocene -like
<br />condition. A continuing trajectory away from the
<br />Holocene could lead, with an uncomfortably high
<br />probability, to a very different state of the Earth
<br />system, one that is likely to be much less hos-
<br />pitable to the development of human societies
<br />(17,13, 20). The PB framework aims to help guide
<br />human societies away from such a trajectory by
<br />defining a "safe operating space" in which we can
<br />continue to develop and thrive. It does this by
<br />proposing boundaries for anthropogenic pertur-
<br />bation of critical Earth - system processes. Respect-
<br />ing these boundaries would greatly reduce the
<br />risk that anthropogenic activities could inadver-
<br />tently drive the Earth system to a much less hos-
<br />pitable state.
<br />Nine processes, each of which is clearly being
<br />modified by human actions, were originally sug-
<br />gested to form the basis of the PB framework (1).
<br />Although these processes are fundamental to
<br />Earth - system functioning, there are many other
<br />ways that Earth - system functioning could be de-
<br />scribed, including potentially valuable metrics
<br />for quantifying the human imprint on it. These
<br />alternative approaches [e.g., (4)] often represent
<br />ways to explore and quantify interactions among
<br />the boundaries. They can provide a valuable com-
<br />plement to the original approach (1) and further
<br />enrich the broader PB concept as it continues to
<br />evolve.
<br />The planetary boundary
<br />framework: Thresholds, feedbacks,
<br />resilience, uncertainties
<br />A planetary boundary as originally defined (1) is
<br />not equivalent to a global threshold or tipping
<br />point. As Fig. 1 shows, even when a global- or
<br />continental /ocean basin -level threshold in an
<br />Faith- system process is likely to exist [e.g., (20, 21)],
<br />the proposed planetary boundary is not placed
<br />at the position of the biophysical threshold but
<br />rather upstream of it —i.e., well before reaching
<br />the threshold. This buffer between the boundary
<br />(the end of the safe operating space, the green
<br />zone in Fig. 1) and the threshold not only ac-
<br />counts for uncertainty in the precise position of
<br />the threshold with respect to the control variable
<br />'Stockholm Resilience Centre, Stockholm University, 10691
<br />Stockholm, Sweden. 'Fenner School of Environment and
<br />Society, The Australian National University, Canberra, ACT 2601,
<br />Australia. tenter for Macroecology, Evolution, and Climate,
<br />University of Copenhagen, Natural History Museum of Denmark,
<br />Universitetsparken 15, Building 3, 2100 Copenhagen, Denmark.
<br />°Department of Natural Resource Sciences and McGill School of
<br />Environment, McGill University, 21, 111 Lakeshore Road, Ste -
<br />Anne-de- Bellevue, QC H9X 3V9, Canada. 5Centre for Studies in
<br />Complexity, Stellenbosch University, Private Bag Xl,
<br />Stellenbosch 7602, South Africa. 6Center for Limnology,
<br />University of Wisconsin, 680 North Park Street, Madison WI
<br />53706 USA. 7Alterra Wageningen University and Research
<br />Centre, P.O. Box 47, 6700AA Wageningen, Netherlands.
<br />8Environmental Systems Analysis Group, Wageningen University,
<br />P.O. Box 47, 6700 AA Wageningen, Netherlands. 'Department
<br />of Environmental Science and Analytical Chemistry, Stockholm
<br />University, 10691 Stockholm, Sweden. 10Beijer Institute of
<br />Ecological Economics, Royal Swedish Academy of Sciences,
<br />SE -10405 Stockholm, Sweden. "Research Domain Earth
<br />System Analysis, Potsdam Institute for Climate Impact
<br />Research (PIK), Telegraphenberg A62, 14473 Potsdam,
<br />Germany. "International Livestock Research Institute, P.O.
<br />Box 30709, Nairobi, 00100 Kenya. 13CSIRO (Commonwealth
<br />Scientific and Industrial Research Organization), St. Lucia,
<br />QLD 4067, Australia. 14Centre for Biodiversity and
<br />Environment Research (CBER), Department of Genetics,
<br />Evolution and Environment, University College London, Gower
<br />Street, London WME 613T, UK. 15Stockholm Environment
<br />Institute, Linnegatan 87D, SE -10451 Stockholm, Sweden.
<br />16Scripps Institution of Oceanography, University of California
<br />at San Diego, 8622 Kennel Way, La Jolla, CA 92037 USA.
<br />17TERI (The Energy and Resources Institute) University, 10
<br />Institutional Area, Vasant Kunj, New Delhi, Delhi 110070,
<br />India. 18Natural Resources and the Environment, CSIR, P.O.
<br />Box 320, Stellenbosch 7599, South Africa. "Division of
<br />History of Science, Technology and Environment, KTH Royal
<br />Institute of Technology, SE -10044 Stockholm, Sweden.
<br />*Corresponding author. E -mail: will.steffen @anu.edu.au
<br />SCIENCE sciencemag.org 13 FEBRUARY 2015 • VOL 347 ISSUE 6223 1259555 -1
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