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Planetary boundaries

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Revision as of 22:27, 19 June 2011 by Gabriel Kielland (talk | contribs) (Human impact on the nitrogen cycle)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff) Not to be confused with Planetary boundary layer.

Planetary boundaries is a concept developed by a group of researchers led by Johan Rockström, director of the Stockholm Resilience Centre. The concept highlights that dangerous thresholds (or tipping points) on global earth-system processes have already been crossed or are being rapidly approached due to human activities. The research was presented in Nature in 2009.

Boundary issue Boundary indicator Status
1. Climate change CO2 in the atmosphere (see also tipping point (climatology)) limit exceeded
2. Biodiversity loss Number of species becoming extinct per million per year (Holocene extinction) limit exceeded
3a. Nitrogen cycle
3b. Phosphorus cycle		 amount of N2 per year due to man removed from the atmosphere
amount of phosphorus per year going into the oceans		 limit exceeded
almost exceeded
4. Atmospheric ozone Stratospheric ozone depletion not exceeded
5. Ocean acidification average degree of seawater saturation in aragonite almost exceeded
6. Global freshwater use consumption of water per capita almost exceeded
7. Change in land use percentage of land used in agriculture almost exceeded
8. Chemical pollution concentration of toxic substances, plastics, endocrine disruptors, heavy metals,
Radioactive contamination into the environment		 not exceeded
9. Atmospheric aerosol loading concentration of particulate in the atmosphere not exceeded

The proposed concept of “planetary boundaries” lays the groundwork for 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 define, as it were, the boundaries of the “planetary playing field” for humanity if major human-induced environmental change on a global scale is to be avoided

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- to planetary-scale systems. The 2009 study identified nine planetary boundaries and, drawing upon current scientific understanding, the researchers proposed quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W/m in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (less than 5% reduction in total atmospheric O3 from a pre-industrial level of 290 Dobson Units); biogeochemical 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 km/yr of consumptive use of runoff resources); land system change (<15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of <10 extinctions per million species). The two additional planetary boundaries for which the group had not yet been able to determine a boundary level are chemical pollution and atmospheric aerosol loading.

Debate

The concept was referred to in the European Environment Agency synthesis report "The European environment – state and outlook 2010". The report questions whether it is meaningful to calculate a global rate for processes some of which are inherently localised, the scientific justification, the possibility of choosing exact values that are non-arbitrary and the problems of reducing the complexity of interactions into single boundary values. Problems might arise with regard to balancing limits with ethical and economic issues and confusing values with targets.

Also the UNEP Yearbook 2010 repeated Rockström's message conceptually linked with Ecosystems management and Environmental Governance.

See also

References

  1. Planetary Boundaries: Specials
  2. The European environment – state and outlook 2010 Chapter 7: environmental challenges in a global context
  3. UNEP Year Book 2010

External links

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