SUSTAINABILITY Planetary boundaries: Guiding human ...

1 R ES E A RC H. space for global societal development. A zone RESEARCH ARTICLE SUMMARY of uncertainty for each PB highlights the area of increasing risk. The current level of anthro- pogenic impact on the ES, and thus the risk to SUSTAINABILITY . the stability of the ES, is assessed by compar- ison with the proposed PB (see the figure). Planetary boundaries: Guiding RESULTS: Three of the PBs (climate change, stratospheric ozone depletion, and ocean acid- human development on a ification) remain essentially unchanged from the earlier analysis. Regional-level boundaries changing planet as well as globally aggregated PBs have now been developed for biosphere integrity (earlier biodiversity loss ), biogeochemical flows, land- Will Steffen,* Katherine Richardson, Johan Rockstr m, Sarah E.

2 Cornell, Ingo Fetzer, system change, and freshwater use. At present, Elena M. Bennett, Reinette Biggs, Stephen R. Carpenter, Wim de Vries, only one regional boundary (south Asian mon- Cynthia A. de Wit, Carl Folke, Dieter Gerten, Jens Heinke, Georgina M. Mace, soon) can be established for atmospheric aerosol Linn M. Persson, Veerabhadran Ramanathan, Belinda Reyers, Sverker S rlin loading. Although we cannot identify a single PB.. for novel entities (here de- ON OUR WEB SITE. INTRODUCTION: There is an urgent need for that we know for certain can support contem- fined as new substances, Downloaded from on October 12, 2019. a new paradigm that integrates the continued porary human societies. There is increasing evi- Read the full article new forms of existing sub- development of human societies and the main- dence that human activities are affecting ES at stances, and modified life tenance of the Earth system (ES) in a resilient functioning to a degree that threatens the re- forms that have the po- and accommodating state.)

3 The Planetary bound- silience of the ES its ability to persist in a tential for unwanted geo- .. ary (PB) framework contributes to such a Holocene-like state in the face of increasing physical and/or biological paradigm by providing a science-based analysis human pressures and shocks. The PB frame- effects), they are included in the PB framework, of the risk that human perturbations will de- work is based on critical processes that reg- given their potential to change the state of the stabilize the ES at the Planetary scale. Here, the ulate ES functioning. By combining improved ES. Two of the PBs climate change and bio- scientific underpinnings of the PB framework scientific understanding of ES functioning with sphere integrity are recognized as core PBs are updated and strengthened.

4 The precautionary principle, the PB framework based on their fundamental importance for the identifies levels of anthropogenic perturbations ES. The climate system is a manifestation of the RATIONALE: The relatively stable, 11,700-year- below which the risk of destabilization of the amount, distribution, and net balance of energy long Holocene epoch is the only state of the ES ES is likely to remain low a safe operating at Earth's surface; the biosphere regulates ma- terial and energy flows in the ES and increases its resilience to abrupt and gradual change. Anthropogenic perturbation levels of four of the ES processes/features (climate change, bio- sphere integrity, biogeochemical flows, and land- system change) exceed the proposed PB (see the figure).

5 CONCLUSIONS: PBs are scientifically based levels of human perturbation of the ES beyond which ES functioning may be substantially altered. Transgression of the PBs thus creates substantial risk of destabilizing the Holocene state of the ES in which modern societies have evolved. The PB framework does not dictate how societies should develop. These are po- litical decisions that must include considera- tion of the human dimensions, including equity, not incorporated in the PB framework. Never- theless, by identifying a safe operating space for humanity on Earth, the PB framework can make a valuable contribution to decision- makers in charting desirable courses for socie- Current status of the control variables for seven of the Planetary boundaries.

6 The green zone tal development.. is the safe operating space, the yellow represents the zone of uncertainty (increasing risk), and the red is a high-risk zone. The Planetary boundary itself lies at the intersection of the green and yellow zones. The control variables have been normalized for the zone of uncertainty; the center of the figure therefore does not represent values of 0 for the control variables. The control variable shown for climate change is atmospheric CO2 concentration. Processes for which global-level boundaries The list of author affiliations is available in the full article online. *Corresponding author. E-mail: cannot yet be quantified are represented by gray wedges; these are atmospheric aerosol loading, Cite this article as W.

7 Steffen et al., Science 347, 1259855. novel entities, and the functional role of biosphere integrity. (2015). DOI: 736 13 FEBRUARY 2015 VOL 347 ISSUE 6223 SCIENCE. R ES E A RC H. risk that anthropogenic activities could inadver- RESEARCH ARTICLE tently drive the Earth system to a much less hos- pitable state. Nine processes, each of which is clearly being SUSTAINABILITY modified by human actions, were originally sug- gested to form the basis of the PB framework (1). Planetary boundaries: Guiding Although these processes are fundamental to Earth-system functioning, there are many other ways that Earth-system functioning could be de- human development on a scribed, including potentially valuable metrics for quantifying the human imprint on it.

8 These changing planet alternative approaches [ , (4)] often represent ways to explore and quantify interactions among the boundaries. They can provide a valuable com- Will Steffen,1,2* Katherine Richardson,3 Johan Rockstr m,1 Sarah E. Cornell,1 plement to the original approach (1) and further Ingo Fetzer,1 Elena M. Bennett,4 Reinette Biggs,1,5 Stephen R. Carpenter,6 enrich the broader PB concept as it continues to Wim de Vries,7,8 Cynthia A. de Wit,9 Carl Folke,1,10 Dieter Gerten,11 Jens Heinke,11,12,13 evolve. Georgina M. Mace,14 Linn M. Persson,15 Veerabhadran Ramanathan,16,17. The Planetary boundary Belinda Reyers,1,18 Sverker S rlin19. framework: Thresholds, feedbacks, resilience, uncertainties The Planetary boundaries framework defines a safe operating space for humanity based Downloaded from on October 12, 2019.

9 On the intrinsic biophysical processes that regulate the stability of the Earth system. A Planetary boundary as originally defined (1) is Here, we revise and update the Planetary boundary framework, with a focus on the not equivalent to a global threshold or tipping underpinning biophysical science, based on targeted input from expert research point. As Fig. 1 shows, even when a global- or communities and on more general scientific advances over the past 5 years. Several of the continental/ocean basin level threshold in an boundaries now have a two-tier approach, reflecting the importance of cross-scale Earth-system process is likely to exist [ , (20, 21)], interactions and the regional-level heterogeneity of the processes that underpin the the proposed Planetary boundary is not placed boundaries.

10 Two core boundaries climate change and biosphere integrity have been at the position of the biophysical threshold but identified, each of which has the potential on its own to drive the Earth system into a new rather upstream of it , well before reaching state should they be substantially and persistently transgressed. the threshold. This buffer between the boundary (the end of the safe operating space, the green T. zone in Fig. 1) and the threshold not only ac- he Planetary boundary (PB) approach (1, 2) could be emitted to and extracted from the en- counts for uncertainty in the precise position of aims to define a safe operating space for vironment ( , chemicals that pollute airsheds the threshold with respect to the control variable human societies to develop and thrive, based or waterways) and on how much the environment on our evolving understanding of the func- could be changed by direct human modification 1.