The Planetary Boundaries framework, developed by researchers at the Stockholm Resilience Centre, defines the environmental limits within which humanity can safely operate. This approach identifies nine Earth system processes that regulate the stability and resilience of the planet, which has remained stable throughout the Holocene (the last 12,000 years). The framework’s primary goal is to quantify the maximum human-induced changes the planet can withstand without risking large-scale, abrupt, or irreversible environmental change. Identifying these biophysical thresholds guides global sustainability efforts within Earth’s natural constraints.
Understanding the Safe Operating Space Framework
The Planetary Boundaries concept is built on the understanding that Earth operates as an integrated, complex, self-regulating system. The framework defines a “Safe Operating Space,” which represents the desirable environmental state for human civilization to thrive. This space is defined by thresholds for key Earth system processes, beyond which the risk of significant environmental change increases sharply.
The framework divides the status of each boundary into three distinct zones based on the measured level of the control variable. The “Safe Operating Space” (green zone) indicates the process is within its boundary and the risk of large-scale change is low. The “Zone of Uncertainty” (yellow zone) means the boundary has been crossed, and the risk of non-linear change begins to rise. Beyond this is the “High-Risk Zone” (red zone), where the system is pushed far past its threshold, increasing the likelihood of damaging, often irreversible, shifts in Earth’s state.
The Nine Core Earth System Boundaries
The framework identifies nine Earth system processes that are fundamental to maintaining the planet’s stability. These boundaries are quantified by specific control variables that track the extent of human influence on each process.
Climate Change
This boundary is controlled by the concentration of carbon dioxide (CO2) in the atmosphere and the resulting change in radiative forcing. The boundary is set to avoid pushing the climate system beyond a state where large-scale, potentially catastrophic changes become likely, such as the irreversible loss of major ice sheets or changes in monsoon systems.
Biosphere Integrity
This boundary addresses the integrity of ecosystems and is considered a core boundary alongside climate change. It is split into two components: genetic diversity, measured by the extinction rate of species, and functional diversity, which tracks the capacity of ecosystems to support life.
Novel Entities
This boundary encompasses the introduction and accumulation of new human-created chemical compounds, including plastics, organic pollutants, heavy metals, and radioactive materials. The boundary is crossed when the production and release of these materials exceed the global capacity for assessment, monitoring, and safe management, leading to significant ecosystem disruption.
Stratospheric Ozone Depletion
This boundary monitors the thinning of the ozone layer in the stratosphere, which protects the Earth from harmful ultraviolet radiation. The control variable is the concentration of stratospheric ozone, which is primarily affected by ozone-depleting substances like chlorofluorocarbons (CFCs).
Atmospheric Aerosol Loading
This boundary focuses on the concentration of particles suspended in the atmosphere, which affect climate, weather patterns, and human health. While the global boundary is not yet quantified, the risk is assessed regionally due to the ability of aerosols to disrupt major climate systems, such as the Asian monsoon.
Ocean Acidification
This process measures the decrease in ocean pH resulting from the absorption of excess atmospheric CO2 by the world’s oceans. Increased acidity harms marine organisms that rely on calcium carbonate to form shells and skeletons, such as corals and certain plankton.
Biogeochemical Flows (Nitrogen and Phosphorus)
This boundary tracks the human alteration of the natural cycles of nitrogen (N) and phosphorus (P), which are essential for life. The excessive use of fertilizers in agriculture has led to massive flows of reactive N and P into the environment, causing widespread water pollution, ocean dead zones, and greenhouse gas emissions.
Freshwater Use
This boundary covers the consumption of water resources, measured by two components. Blue water refers to visible water in rivers, lakes, and aquifers, while green water is the water held in soil and plants. Excessive use of both forms stresses ecosystems and impacts agriculture, with the green water component being relevant for terrestrial ecosystem health.
Land-System Change
This boundary is defined by the proportion of the planet’s ice-free land surface that has been converted from natural ecosystems, such as forests and wetlands, to human uses like cropland. Large-scale land conversion impacts biodiversity, affects carbon storage, and alters the exchange of water and energy between the land and the atmosphere.
Current Status and Transgressed Boundaries
Recent scientific assessments indicate that Earth is currently outside of the Safe Operating Space, with six of the nine planetary boundaries now considered transgressed. The transgression of these boundaries suggests an elevated risk of triggering non-linear environmental changes.
Climate Change and Biosphere Integrity were among the first boundaries identified as transgressed due to their fundamental role in regulating the Earth system. For Climate Change, the concentration of CO2 in the atmosphere is significantly above the proposed boundary of 350 parts per million (ppm). Biosphere Integrity is transgressed in both its genetic and functional components, indicated by species extinction rates far exceeding the natural background rate.
The Biogeochemical Flows boundary is also in the high-risk zone due to the massive anthropogenic release of reactive nitrogen and phosphorus into the environment. The Land-System Change boundary has been crossed, reflecting the extensive conversion of natural land, particularly forests, for agriculture and other human uses.
The boundary for Novel Entities, which includes chemical pollution and microplastics, has been quantified and is assessed as transgressed. The Freshwater Use boundary is also considered crossed for both its blue water and green water components. Only Stratospheric Ozone Depletion and Ocean Acidification, while showing negative trends, are currently assessed as being within the Safe Operating Space or Zone of Uncertainty, respectively.
Interconnectedness and Systemic Global Risk
The nine Planetary Boundaries do not function in isolation but are interconnected within the Earth system. Crossing one boundary often creates feedback loops that increase pressure on others, creating a systemic risk greater than the sum of individual risks. For example, transgressing the Climate Change boundary through greenhouse gas emissions directly contributes to transgressing the Ocean Acidification boundary.
Human actions that impact one area can have cascading effects across the system. Deforestation, which crosses the Land-System Change boundary, releases stored carbon, exacerbating Climate Change, and simultaneously destroys habitat, further crossing the Biosphere Integrity boundary. This network of interactions means that pushing one boundary past its threshold can lower the safe threshold for another, potentially driving the entire system toward an undesirable state.