摘要：Anthropogenic pressures on the Earth System have reached a scale where abrupt globalenvironmental change can no longer be excluded. We propose a new approach to global sustainability inwhich 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 ofcrossing thresholds that will trigger non-linear, abrupt environmental change within continental- toplanetary-scale systems. We have identified nine planetary boundaries and, drawing upon current scientificunderstanding, we propose quantifications for seven of them. These seven are climate change (CO2concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m-2in radiative forcing);ocean acidification (mean surface seawater saturation state with respect to aragonite ≥80% of pre-industriallevels); stratospheric ozone (<5% reduction in O3concentration from pre-industrial level of 290 DobsonUnits); biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N2to 35 Tg N yr-1)and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural backgroundweathering of P); global freshwater use (<4000 km3yr-1of consumptive use of runoff resources); landsystem change (<15% of the ice-free land surface under cropland); and the rate at which biological diversityis lost (annual rate of <10 extinctions per million species). The two additional planetary boundaries forwhich we have not yet been able to determine a boundary level are chemical pollution and atmosphericaerosol loading. We estimate that humanity has already transgressed three planetary boundaries: for climatechange, rate of biodiversity loss, and changes to the global nitrogen cycle. Planetary boundaries areinterdependent, because transgressing one may both shift the position of other boundaries or cause themto be transgressed. The social impacts of transgressing boundaries will be a function of the social–ecologicalresilience of the affected societies. Our proposed boundaries are rough, first estimates only, surrounded bylarge uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth Systemand resilience science. The proposed concept of "planetary boundaries" lays the groundwork for shiftingour approach to governance and management, away from the essentially sectoral analyses of limits togrowth aimed at minimizing negative externalities, toward the estimation of the safe space for humandevelopment. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" forhumanity if we want to be sure of avoiding major human-induced environmental change on a global scale
关键词：atmospheric aerosol loading; biogeochemical nitrogen cycle; biological diversity; chemical;pollution; climate change; Earth; global freshwater use; land system change; ocean acidification;phosphorus cycle; planetary boundaries; stratospheric ozone; sustainability
