Research Article

Planetary boundaries: Guiding human development on a changing planet

See allHide authors and affiliations

Science  13 Feb 2015:
Vol. 347, Issue 6223, 1259855
DOI: 10.1126/science.1259855
  • Current status of the control variables for seven of the planetary boundaries.

    The green zone 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 cannot yet be quantified are represented by gray wedges; these are atmospheric aerosol loading, novel entities, and the functional role of biosphere integrity.

  • Fig. 1 The conceptual framework for the planetary boundary approach, showing the safe operating space, the zone of uncertainty, the position of the threshold (where one is likely to exist), and the area of high risk.

    Modified from (1).

  • Fig. 2

    The subglobal distributions and current status of the control variables for (A) biogeochemical flows of P; (B) biogeochemical flows of N; (C) land-system change; and (D) freshwater use. In each panel, green areas are within the boundary (safe), yellow areas are within the zone of uncertainty (increasing risk), and red areas are beyond the zone of uncertainty (high risk). Gray areas in (A) and (B) are areas where P and N fertilizers are not applied; in (C), they are areas not covered by major forest biomes; and in (D), they are areas where river flow is very low so that environmental flows are not allocated. See Table 1 for values of the boundaries and their zones of uncertainty and (33) for more details on methods and results.

  • Fig. 3

    The current status of the control variables for seven of the nine planetary boundaries. The green zone is the safe operating space (below the boundary), yellow represents the zone of uncertainty (increasing risk), and red is the high-risk zone. The planetary boundary itself lies at the inner heavy circle. The control variables have been normalized for the zone of uncertainty (between the two heavy circles); 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 cannot yet be quantified are represented by gray wedges; these are atmospheric aerosol loading, novel entities, and the functional role of biosphere integrity. Modified from (1).

  • Table 1 The updated control variables and their current values, along with the proposed boundaries and zones of uncertainty, for all nine planetary boundaries.

    In the first column, the name for the Earth-system process used in the original PB publication (R2009, reference 1) is given for comparison.

    Earth-system
    process
    Control
    variable(s)
    Planetary boundary
    (zone of uncertainty)
    Current value of
    control variable
    Climate
    change
    (R2009:
    same)
    Atmospheric CO2
    concentration, ppm
    Energy imbalance
    at top-of-
    atmosphere, W m-2
    350 ppm CO2 (350-450 ppm)
    +1.0 W m-2 (+1.0-1.5 W m-2)
    398.5 ppm CO2
    2.3 W m-2
    (1.1-3.3 W m-2)
    Change in
    biosphere
    integrity
    (R2009:
    Rate of
    biodiversity
    loss)
    Genetic diversity:
    Extinction rate
    Functional diversity:
    Biodiversity
    Intactness Index (BII)
    Note: These are
    interim control
    variables until more
    appropriate ones are
    developed
    < 10 E/MSY (10-100 E/MSY)
    but with an aspirational goal of
    ca. 1 E/MSY (the background
    rate of extinction loss). E/MSY =
    extinctions per million species-years
    Maintain BII at 90% (90-30%)
    or above, assessed
    geographically by biomes/large
    regional areas (e.g. southern
    Africa), major marine
    ecosystems (e.g., coral reefs) or
    by large functional groups
    100-1000 E/MSY
    84%, applied to
    southern Africa
    only
    Stratospheric
    ozone
    depletion
    (R2009: same)
    Stratospheric O3
    concentration, DU
    <5% reduction from pre-
    industrial level of 290 DU
    (5%–10%), assessed by
    latitude
    Only transgressed
    over Antarctica in
    Austral spring
    (~200 DU)
    Ocean
    acidification
    (R2009:
    same)
    Carbonate ion
    concentration,
    average global
    surface ocean
    saturation state with
    respect to aragonite
    arag)
    ≥80% of the pre-industrial
    aragonite saturation state of
    mean surface ocean, including
    natural diel and seasonal
    variability (≥80%– ≥70%)
    ~84% of the
    pre-industrial
    aragonite
    saturation state
    Biogeochemical
    flows: (P and
    N cycles)
    (R2009:
    Biogeochemical
    flows: (interference
    with P and N
    cycles))
    P Global: P flow
    from freshwater
    systems into the
    ocean
    P Regional: P flow
    from fertilizers to
    erodible soils
    N Global: Industrial
    and intentional
    biological fixation
    of N
    11 Tg P yr-1 (11-100 Tg P yr-1)
    6.2 Tg yr-1 mined and applied to
    erodible (agricultural) soils
    (6.2-11.2 Tg yr-1). Boundary is a
    global average but regional
    distribution is critical for
    impacts.
    62 Tg N yr-1 (62-82 Tg N yr-1).
    Boundary acts as a global
    ‘valve’ limiting introduction of
    new reactive N to Earth System,
    but regional distribution of
    fertilizer N is critical for
    impacts.
    ~22 Tg P yr-1
    ~14 Tg P yr-1
    ~150 Tg N yr-1
    Land-system
    change
    (R2009:
    same)
    Global: Area of
    forested land as %
    of original forest
    cover
    Biome: Area of
    forested land as %
    of potential forest
    Global: 75% (75-54%) Values
    are a weighted average of the
    three individual biome
    boundaries and their uncertainty
    zones
    Biome:
    Tropical: 85% (85-60%)
    Temperate: 50% (50-30%)
    Boreal: 85% (85-60%)
    62%
    Freshwater
    use
    (R2009:
    Global
    freshwater
    use)
    Global: Maximum
    amount of
    consumptive blue
    water use (km3yr-1)
    Basin: Blue water
    withdrawal as % of
    mean monthly river
    flow
    Global: 4000 km3 yr-1
    (4000-6000 km3 yr-1)
    Basin: Maximum monthly
    withdrawal as a percentage
    of mean monthly river flow.
    For low-flow months: 25%
    (25-55%); for intermediate-
    flow months: 30% (30-60%);
    for high-flow months: 55%
    (55-85%)
    ~2600 km3 yr-1
    Atmospheric
    aerosol
    loading
    (R2009:
    same)
    Global: Aerosol
    Optical Depth
    (AOD), but much
    regional variation
    Regional: AOD as
    a seasonal average
    over a region. South
    Asian Monsoon
    used as a case study
    Regional: (South Asian
    Monsoon as a case study):
    anthropogenic total (absorbing
    and scattering) AOD over
    Indian subcontinent of 0.25
    (0.25-0.50); absorbing
    (warming) AOD less than 10%
    of total AOD
    0.30 AOD, over
    South Asian
    region
    Introduction
    of novel entities
    (R2009: Chemical
    pollution)
    No control variable
    currently defined
    No boundary currently
    identified, but see boundary
    for stratospheric ozone for an
    example of a boundary
    related to a novel entity (CFCs)

Supplementary Materials

  • Planetary boundaries: Guiding human development on a changing planet

    Will Steffen, Katherine Richardson, Johan Rockström, Sarah E. Cornell, Ingo Fetzer, Elena M. Bennett, R. Biggs, Stephen R. Carpenter, Wim de Vries, Cynthia A. de Wit, Carl Folke, Dieter Gerten, Jens Heinke, Georgina M. Mace, Linn M. Persson, Veerabhadran Ramanathan, B. Reyers, Sverker Sörlin

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Methods
    • Figs. S1 to S10
    • Tables S1 to S3
    • References

Navigate This Article