Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockstrom and colleagues.

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A safe operating space for humanity

Plastics have outgrown most man-made materials and have long been under environmental scrutiny. However, robust global information, particularly about their end-of-life fate, is lacking. By identifying and synthesizing dispersed data on production, use, and end-of-life management of polymer resins, synthetic fibers, and additives, we present the first global analysis of all mass-produced plastics ever manufactured. We estimate that 8300 million metric tons (Mt) as of virgin plastics have been produced to date. As of 2015, approximately 6300 Mt of plastic waste had been generated, around 9% of which had been recycled, 12% was incinerated, and 79% was accumulated in landfills or the natural environment. If current production and waste management trends continue, roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050.

Production, use, and fate of all plastics ever made

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

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Planetary boundaries: Guiding human development on a changing planet

Protecting the world’s freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world’s population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.

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Global threats to human water security and river biodiversity

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.

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Planetary boundaries: Exploring the safe operating space for humanity

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Planting Power: The Afforestation of the Commons and State Formation in Portugal

T Pacific and its islands have long held allure for romantics and scientists alike. The ocean’s great size and galaxies of islands make it as appealing to botanists and biogeographers as to beachcombers. It also has seductive charms for those interested in environmental history, in the changing mutual influence of human communities and the earth, air, water, and life forms that sustain them. In the last three years, two books have appeared that emphasize the relevance of the environmental history of Easter Island to that of planet earth.1 But Easter Island, like most Pacific islands—indeed, most islands anywhere—has had a particularly tumultuous environmental history. Evolution and history have conspired to give island peoples especially unstable environments. The island world of the Pacific shows the transforming power of intrusive species, including Homo sapiens, and of their efforts to secure niches for themselves. In human terms that effort includes economic activity, which is particularly capable of

Of Rats and Men: A Synoptic Environmental History of the Island Pacific*

Natives and Exotics: World War II and environment in the South Pacific. By Judith A. Bennett. Honolulu: University of Hawai‘i Press, 2009. xxvi+439 pp., maps, illus, notes, bibliog., index. ISBN 97...

Natives and Exotics

In Collapse: How Societies Choose to Fail or Succeed, Jared Diamond claims that several societies in times past collapsed in part for environmental reasons and that these cases bear lessons for today. By and large, Diamond has got his history right. But the application of lessons derived from these historical cases to today's environmental problems will leave many readers unconvinced. Scaling up from diminutive, isolated, and low-technology examples such as precontact Easter Island or the Greenland Norse to the contemporary world is fraught with conceptual difficulties, not all of which Diamond can dispel. Diamond's arguments, whether one finds them convincing or not, raise some timely questions. Are we indeed at serious risk of environmental collapse? And how do some current trends—the rise of China, the coming transition to a new energy regime, and the slowing of population growth—affect the chances of environmental collapse?

John Robert McNeill

Papers

Planting Power: The Afforestation of the Commons and State Formation in Portugal

Of Rats and Men: A Synoptic Environmental History of the Island Pacific*

Natives and Exotics

Diamond in the Rough: Is There a Genuine Environmental Threat to Security? A Review Essay

Wetlands as the intersection of soils, water and indigenous human society in the Americas.