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

:The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

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Soil carbon sequestration impacts on global climate change and food security.

The resilience perspective is increasingly used as an approach for understanding the dynamics of social–ecological systems. This article presents the origin of the resilience perspective and provides an overview of its development to date. With roots in one branch of ecology and the discovery of multiple basins of attraction in ecosystems in the 1960–1970s, it inspired social and environmental scientists to challenge the dominant stable equilibrium view. The resilience approach emphasizes non-linear dynamics, thresholds, uncertainty and surprise, how periods of gradual change interplay with periods of rapid change and how such dynamics interact across temporal and spatial scales. The history was dominated by empirical observations of ecosystem dynamics interpreted in mathematical models, developing into the adaptive management approach for responding to ecosystem change. Serious attempts to integrate the social dimension is currently taking place in resilience work reflected in the large numbers of sciences involved in explorative studies and new discoveries of linked social–ecological systems. Recent advances include understanding of social processes like, social learning and social memory, mental models and knowledge–system integration, visioning and scenario building, leadership, agents and actor groups, social networks, institutional and organizational inertia and change, adaptive capacity, transformability and systems of adaptive governance that allow for management of essential ecosystem services.

Resilience: the emergence of a perspective for social-ecological systems analyses

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

▪ Abstract We explore the social dimension that enables adaptive ecosystem-based management. The review concentrates on experiences of adaptive governance of social-ecological systems during periods of abrupt change (crisis) and investigates social sources of renewal and reorganization. Such governance connects individuals, organizations, agencies, and institutions at multiple organizational levels. Key persons provide leadership, trust, vision, meaning, and they help transform management organizations toward a learning environment. Adaptive governance systems often self-organize as social networks with teams and actor groups that draw on various knowledge systems and experiences for the development of a common understanding and policies. The emergence of “bridging organizations” seem to lower the costs of collaboration and conflict resolution, and enabling legislation and governmental policies can support self-organization while framing creativity for adaptive comanagement efforts. A resilient social-eco...

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Adaptive governance of social-ecological systems

The reservoir, or “box”, model is a useful starting point for studies of chemical tracers The model can be derived from the chemical transport equation for a continuous ocean and thus rests on a sound physical foundation The assumption that the tracers are well-mixed inside each reservoir is discussed and found unnecessary The model is well adapted for dealing with sets of chemical tracers which simultaneously undergo chemical reactions, isotopic fractionation, radioactive decay, and exchange with the atmosphere In this article we relate the transfer coefficients of the reservoir model to the advective and diffusive coefficients of the space-averaged chemical transport equation for a continuous ocean, and we develop general methods for applying the reservoir model to a large suite of nonconservative chemical tracers In an article which follows we apply the concepts of this article to a study of eight chemical tracers in the Pacific Ocean DOI: 101111/j2153-34901967tb01509x

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.2153-3490.1967.tb01509.x

The simultaneous use of chemical tracers in oceanic studies I. General theory of reservoir models

The previous work by Rossby and Cahn on the adjustment of a non-balanced velocity field towards geostrophic equilibrium has been generalized to incorporate the corresponding process in a stratified but incompressible fluid. It is shown that the character of the process essentially depends upon the width of the current, the velocity profile in the vertical and the vertical density gradient. As long as the vertical density gradient is small the adjustment of the mean motion of the fluid ( ) exactly corresponds to the one described by Cahn. On the other hand vertical variations of the unbalanced motion will set up internal oscillations which have considerable larger (vertical) amplitudes than is found for the adjustment of the mean motion. Furthermore, the speed of propagation of the gravity inertia waves thus generated (c K ) is considerably smaller than that of the waves generated during the adjustment of the mean motion (c 0 ). For values of the vertical density gradient as found in the oceans c K < 0.05 c 0 . In the final state of equilibrium the mean motion of the fluid will be approximately the same as before the adjustment, while a considerable smoothing of the vertical gradients of the velocity field will take place, the more the broader the original current is. DOI: 10.1111/j.2153-3490.1953.tb01068.x

The Adjustment of a Non-balanced Velocity Field towards Geostrophic Equilibrium in a Stratified Fluid

Measurements of the CO 2 content in the troposphere and lower stratosphere are presented. The seasonal variations at 5 km, 7 km, 9 km and 11 km at 60° are shown, at the last to levels both in tropospheric and stratospheric air. A comparison with previous data confirms that an annual increase of the CO 2 content of the atmosphere by 0.7 ppm occurs. Data from the Indian Ocean and the Atlantic Ocean (30° N) are presented. DOI: 10.1111/j.2153-3490.1966.tb00221.x

Space and time variations of the CO 2 content of the troposphere and lower stratosphere

Salinity, oxygen, inorganic phosphorus, organic and inorganic carbon, carbonate alkalinity, insoluble carbonate, and radiocarbon are used simultaneously as tracers to investigate oceanic circulation, chemical processes within the ocean and chemical exchange at oceanic boundaries. Estimates of the rates of these processes are made using the equation for chemical transport in the simplest approximation which recognizes spatially variable exchange at the ocean-atmosphere boundary, horizontal and vertical advective and eddy diffusive transport, and gravitational settling of insoluble chemicals within the oceans. This approximation is a cyclic model with one atmospheric and three oceanic reservoirs between which tracers exchange by first-order kinetics. Data for the Pacific Ocean are used after having been averaged over time and the regions: warm surface water, cold surface water, and deep water. Northern and southern cold surface waters are treated as alternate cases. We deduce that: 1 The mass of deep water in the Pacific Ocean divided by its rate of production is about 1100 years, a time interval in close agreement with its average radiocarbon age relative to that of cold surface water. 2 In the South Pacific Ocean, the transfer of water between the deep ocean and the surface is principally by exchange with cold surface water. A small net circulation from warm surface water to cold surface water is suggested by the model, but the rate cannot be calculated with existing information. 3 The three-reservoir model cannot, even to a first approximation, explain the circulation of the North Pacific Ocean, because it overlooks the flow of deep water into the North Pacific Ocean from the South Pacific Ocean. 4 Both oxygen and carbon dioxide are evolved from surface waters at low latitudes and absorbed at high latitudes. The rates of exchange from warm surface water to cold surface water are of the order of 10 17 mmol yr ?1 . 5 About 10% of the inorganic carbon in deep water arrives there from surface water by gravitational settling of organic carbon and insoluble carbonate. The other 90% is transported there by the water itself. 6 The use of pH measurements to assay for dissolved inorganic carbon and alkalinity seriously limits the reliability of carbon data in the present study. Small errors in pH result in large uncertainties in the deduced rates of gravitational transport of organic carbon and insoluble carbonates and in the rate of exchange of CO 2 with the atmosphere. DOI: 10.1111/j.2153-3490.1968.tb00348.x

The simultaneous use of chemical tracers in oceanic studies II. A three‐reservoir model of the North and South Pacific Oceans

Equity is of fundamental concern in the quest for international cooperation to stabilize greenhouse gas concentrations by the reduction of emissions. By modeling the carbon cycle, we estimate the global CO(2) emissions that would be required to stabilize the atmospheric concentration of CO(2) at levels ranging from 450 to 1,000 ppm. These are compared, on both an absolute and a per-capita basis, to scenarios for emissions from the developed and developing worlds generated by socio-economic models under the assumption that actions to mitigate greenhouse gas emissions are not taken. Need and equity have provided strong arguments for developing countries to request that the developed world takes the lead in controlling its emissions, while permitting the developing countries in the meantime to use primarily fossil fuels for their development. Even with major and early control of CO(2) emissions by the developed world, limiting concentration to 450 ppm implies that the developing world also would need to control its emissions within decades, given that we expect developing world emissions would otherwise double over this time. Scenarios leading to CO(2) concentrations of 550 ppm exhibit a reduction of the developed world's per-capita emission by about 50% over the next 50 years. Even for the higher stabilization levels considered, the developing world would not be able to use fossil fuels for their development in the manner that the developed world has used them.

https://www.pnas.org/content/pnas/98/9/4850.full.pdf

Bert Bolin

Papers

The simultaneous use of chemical tracers in oceanic studies I. General theory of reservoir models

The Adjustment of a Non-balanced Velocity Field towards Geostrophic Equilibrium in a Stratified Fluid

Space and time variations of the CO 2 content of the troposphere and lower stratosphere

The simultaneous use of chemical tracers in oceanic studies II. A three‐reservoir model of the North and South Pacific Oceans

On strategies for reducing greenhouse gas emissions