COP10.org

Ecology and Society
14(2): 32 - 2009
Source article here.

by Rockström, J., W. Steffen, K. Noone, Å. Persson, F. S. Chapin, III, E. Lambin, T. M. Lenton, M. Scheffer, C. Folke, H. Schellnhuber, B. Nykvist, C. A. De Wit, T. Hughes, S. van der Leeuw, H. Rodhe, S. Sörlin, P. K. Snyder, R. Costanza, U. Svedin, M. Falkenmark, L. Karlberg, R. W. Corell, V. J. Fabry, J. Hansen, B. Walker, D. Liverman, K. Richardson, P. Crutzen, and J. Foley.

ABSTRACT

Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. 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. We have identified nine planetary boundaries and, drawing upon current scientific understanding, we propose 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^-2 in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (<5% reduction in O₃ concentration from pre-industrial level of 290 Dobson Units); biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N₂ to 35 Tg N yr^-1) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P); global freshwater use (<4000 km³ yr^-1 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 we have not yet been able to determine a boundary level are chemical pollution and atmospheric aerosol loading. We estimate that humanity has already transgressed three planetary boundaries: for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle. Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed. The social impacts of transgressing boundaries will be a function of the social–ecological resilience of the affected societies. Our proposed boundaries are rough, first estimates only, surrounded by large uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth System and resilience science. The proposed concept of “planetary boundaries” lays the groundwork for shifting our 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 we want to be sure of avoiding major human-induced environmental change on a global scale.

Excerpt:

HUMANITY HAS ALREADY TRANSGRESSED AT LEAST THREE PLANETARY BOUNDARIES

We have attempted to quantify the temporal trajectory of seven of the proposed planetary boundaries from pre-industrial levels to the present (Fig. 6) (see Appendix 1, Supplementary Methods 2 for data sources and data treatment). The acceleration of the human enterprise since the 1950s, particularly the growth of fertilizer use in modern agriculture, resulted in the transgression of the boundary for the rate of human interference with the global nitrogen cycle. Aggregate data over longer time periods for the biodiversity boundary are not available, but the boundary definition proposed here is greatly exceeded (even out of scale in Fig. 6, illustrated by the shading). We are not suggesting that the current state of biodiversity has passed a boundary. We are saying that the world cannot sustain the current rate of loss of species without resulting in functional collapses. It was not until the 1980s that humanity approached the climate boundary, but the trend of higher atmospheric CO₂ concentration shows no signs of slowing down. In contrast, as a result of the signing of the Montreal Protocol, humanity succeeded in reversing the trend with regard to the stratospheric ozone boundary in the 1990s. As seen from Fig. 6, our estimates indicate that humanity is approaching, moreover at a rapid pace, the boundaries for freshwater use and land-system change. The ocean acidification boundary is at risk, although there is a lack of time-series data for the selected boundary variable, as well as information on the response of marine organisms and ecosystems to the projected CO₂ perturbation.

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