A brief overview of the original concept of planetary boundaries and its advancements
- Global environmental boundaries and the planetary boundaries framework
- 2015 - Building on the original concept of planetary boundaries (PBs): Guiding human development on a changing planet
- Safe and fair limits to the Earth’s system
- Planetary Constraints Revisited in 2023 (PBs 3.0): Earth exceeds six of the nine planetary constraints
The concept of planetary boundaries, first introduced in 2009, provided a framework for understanding the limits of our planet. Over the years, researchers have built on the concept, analysing the dynamic relationships between constraints and the importance of respecting them for the stability of Earth’s systems. Join us on a journey through the evolution of this key concept that shapes science and policy.
Global environmental boundaries and the planetary boundaries framework
Our planet Earth is a complex system sustained by diverse natural processes, ecosystems and life forms. Like our bodies, the Earth operates within constraints that allow life as we know it to exist – called planetary boundaries.
The concept of planetary boundaries was developed to help us understand and respect the limits that define the safe zone within which humanity can thrive, while maintaining the delicate balance of our planet’s ecosystems. They provide a framework for visualising and quantifying the thresholds that must not be crossed if we are to maintain the stability of Earth’s processes.
Understanding the concept of planetary boundaries is key to making informed decisions, taking responsible action and working together to build a sustainable and harmonious relationship with our home planet.
Before presenting the key findings of recent research, we will break down the fundamental aspects of planetary boundaries, such as: planetary processes, constraints, tipping points, and their transgressions and risks.
The concept of planetary boundaries was developed to help us understand and respect the limits that define the safe zone within which humanity can thrive, while maintaining the delicate balance of our planet’s ecosystems. They provide a framework for visualising and quantifying the thresholds that must not be crossed if we are to maintain the stability of Earth’s processes.
Understanding the concept of planetary boundaries is key to making informed decisions, taking responsible action and working together to build a sustainable and harmonious relationship with our home planet.
Before presenting the key findings of recent research, we will break down the fundamental aspects of planetary boundaries, such as: planetary processes, constraints, tipping points, and their transgressions and risks.
2015 – Building on the original concept of planetary boundaries (PBs): Guiding human development on a changing planet
The original 2009 concept of planetary boundaries: Exploring a safe space for humanity to operate
1. Processes and interactions in the Earth’s system
The Earth is a complexly interconnected and dynamic system in which different components interact and influence each other. The interactions of the Earth system include the complex relationships between the geosphere (the solid base of the Earth), the hydrosphere (bodies of water), the atmosphere (the air and gases that surround the planet), the biosphere (living organisms) and the anthroposphere (humans and their activities). Understanding these interactions is key to understanding how changes in one component can cascade down through the whole system, with far-reaching consequences.
1.1 Geosphere-biosphere interactions
The geosphere, which encompasses the physical and inorganic properties of the Earth, interacts significantly with the biosphere, the realm of living organisms. These interactions have historically influenced the state of the Earth.
1.2 Climate regulation
The Earth’s climate is a dynamic system that is regulated by a variety of factors, including solar radiation, greenhouse gases and ocean currents. Climate regulation is key to maintaining stable and liveable conditions.
1.3 Water cycle/Hydrological cycle
The continuous movement of water on, above and below the Earth’s surface involves processes such as evaporation, condensation, precipitation and runoff, which play a key role in shaping landscapes and sustaining life.
1.4 Biogeochemical cycles
Cycles such as the carbon, nitrogen and phosphorus cycles involve the movement of elements between the biosphere, geosphere, atmosphere and hydrosphere, affecting life processes and environmental conditions.
1.5 Biodiversity dynamics
This covers the diversity of life on Earth and the ecological processes that sustain it. Biodiversity dynamics involve interactions between different species and ecosystems, which contribute to the resilience and stability of ecosystems.
1.6 Solar energy input
Solar radiation is the main external source of energy for the Earth. It drives the climate, weather patterns and various processes of the Earth system. Understanding solar input is crucial for assessing environmental change.
2. Planetary boundaries
Planetary boundaries are thresholds that define a safe space for humanity to operate within the Earth system. They mark the limits that must not be crossed, otherwise human activities can cause disruptions to Earth’s key processes. These limits determine the value of parameters for climate change, biosphere integrity, land use, freshwater use, among others. Transgressing these constraints can lead to abrupt or permanent changes, posing serious risks to ecosystems and societies (Rockström et al., 2009; Steffen et al., 2015).
3. Tipping points
Tipping points are critical thresholds in the Earth system at which a small disturbance can cause large and often irreversible changes. Crossing a tipping point can trigger abrupt changes in climate patterns, ecosystems or other processes on Earth. Identifying and understanding these tipping points is key to avoiding potentially catastrophic consequences. An example is the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC), one of the key ocean current systems (Lenton et al., 2008).
4. Overruns and risks
In the field of planetary boundaries, a transgression is the crossing of a critical limit (threshold), which means that human activities have pushed the Earth’s essential systems beyond their sustainable limits (Steffen et al., 2015). These boundaries, which were originally set as precautionary measures, mark the points at which abrupt and potentially irreversible changes in ecological processes crucial for maintaining the Earth’s stability can occur (Rockström et al., 2009) (Fig. II.1.).
A conceptual framework for the Planetary boundary approach, showing the Safe operating space, the Zone of uncertainty: Increasing risk of impacts, the position of the Threshold where it is likely to exist (Process X), and the Dangerous level: High risk of serious impacts.
The original planetary constraints concept from 2009
The concept of Planetary Constraints, introduced in 2009 by Johan Rockström et al, represents a fundamental shift in our understanding of, and relationship to, the Earth’s fragile ecosystems. In their seminal paper, Planetary Constraints: *Exploring a safe space for humanity to operate, they present a framework describing nine critical processes of the Earth system that define safe limits within which humanity can operate and avoid catastrophic consequences for the environment. These processes are climate change, the introduction of new entities, stratospheric ozone depletion, aerosol loading, ocean acidification, biogeochemical fluxes, freshwater use, land use and biosphere integrity.
*Rockström et al., 2009: Planetary Boundaries: Exploring the Safe Operating Space for Humanity
2015 - Building on the original concept of Planetary Boundaries (PBs): Guiding human development on a changing planet
In 2015, Will Steffen and his team built on the concept of planetary boundaries. Their research provided a more detailed breakdown of the dynamic relationships between different constraints and introduced specific indicators to monitor them. In addition to updated data, they have also deepened the understanding of the consequences of exceeding these limits. In addition to global constraints such as climate change and biosphere integrity, researchers have highlighted the importance of regional constraints such as the South Asian monsoon, which has key impacts on agriculture and water supply in the region.
The authors noted that decisions on social development are largely political and that equity should play a central role in these decisions. The consequences of exceeding planetary limits are often unevenly distributed – vulnerable regions such as South Asia feel the impacts of climate change the most, despite having contributed the least to its occurrence. It is therefore imperative that developed countries take greater responsibility for addressing these global challenges, both financially and technically, to ensure a more equitable transition to a sustainable future.
The authors noted that decisions on social development are largely political and that equity should play a central role in these decisions. The consequences of exceeding planetary limits are often unevenly distributed – vulnerable regions such as South Asia feel the impacts of climate change the most, despite having contributed the least to its occurrence. It is therefore imperative that developed countries take greater responsibility for addressing these global challenges, both financially and technically, to ensure a more equitable transition to a sustainable future.
Safe and fair limits to the Earth system
The interconnection between the stability of the Earth and human well-being is often underestimated. In their paper “Safe and fair limits to the Earth system”, Rockström et al. refine the concept of planetary limits and introduce the principle of equity and fairness. They emphasise the inextricable link between environmental sustainability and social justice. The researchers present a set of Earth system constraints covering climate, biosphere, freshwater, nutrients and air pollution at global and sub-global scales.
Seven of the eight limits have already been exceeded, affecting 86% of the world’s population. The need for immediate action to protect Earth’s systems and people is underlined.
Seven of the eight limits have already been exceeded, affecting 86% of the world’s population. The need for immediate action to protect Earth’s systems and people is underlined.
Planetary Constraints Revisited in 2023 (PBs 3.0): Earth exceeds six of the nine planetary constraints
In September 2023, a third version of the planetary boundaries concept (PBs 3.0) was presented in the paper “Earth exceeds six of the nine planetary boundaries” (Richardson et al., 2023). An international team of scientists has further defined planetary resilience as a safe space for humanity to operate. Based on the updated framework, the group concluded that six of the nine limits have been exceeded, meaning that the Earth is outside the safe operating range. Ocean acidification is close to being exceeded, aerosol loading is regionally above the limit, and stratospheric ozone levels have improved slightly. The exceedance rate has increased for all exceedances. The proposed control variable is the proportion of net primary production that is exploited by humans, which also exceeds the limits. The total overruns represent a critical increase in risks to people and ecosystems, threatening the stability of the planet.
Six of the nine limits are exceeded. Ocean acidification is approaching the limit. The green area is the safe operating zone, yellow and red indicate increasing risk and purple indicates the high risk area. Control variables are normalised to mid-Holocene conditions. The exceedances reflect a pronounced human disturbance of the Earth system with high scientific uncertainty.
New methodologies have enabled the quantification of constraints for new entities including chemical compounds, microplastics and nuclear waste. For freshwater use, both green and blue water are taken into account – both limits are exceeded. A new approach to assessing the integrity of the biosphere reveals that this limit was already exceeded at the end of the 19th century. The use of large-scale computer models and simulations was key to this study.
New methodologies have enabled the quantification of constraints for new entities including chemical compounds, microplastics and nuclear waste. For freshwater use, both green and blue water are taken into account – both limits are exceeded. A new approach to assessing the integrity of the biosphere reveals that this limit was already exceeded at the end of the 19th century. The use of large-scale computer models and simulations was key to this study.
Two key elements are of paramount importance in the context of planetary constraints, the functional integrity of the biosphere and climate change. The functional integrity of the biosphere emphasises the integrated conservation of biodiversity and ecosystems, while climate change is central to preventing catastrophic global warming and maintaining a stable climate. Understanding and managing these fundamental constraints is key to a sustainable future.
Central planetary constraints: Climate change and biosphere integrity
Climate change and biosphere integrity
Two key elements are of paramount importance in the context of planetary constraints: the functional integrity of the biosphere and climate change. The functional integrity of the biosphere emphasises the integrated conservation of biodiversity and ecosystems, while climate change is central to preventing catastrophic global warming and maintaining a stable climate. Understanding and managing these fundamental constraints is key to a sustainable future.
Two key elements are of paramount importance in the context of planetary constraints: the functional integrity of the biosphere and climate change. The functional integrity of the biosphere emphasises the integrated conservation of biodiversity and ecosystems, while climate change is central to preventing catastrophic global warming and maintaining a stable climate. Understanding and managing these fundamental constraints is key to a sustainable future.
1. Climate change
Climate change is a core planetary constraint, key to the stability of the Earth and inextricably linked to the biosphere, the atmosphere and human activities. The main problem is anthropogenic emissions of greenhouse gases:
The aim of ensuring climate stability is to limit greenhouse gas concentrations to below 350 ppm CO₂. The key in terms of limiting the Earth system is:
Currently, the radiative forcing is 2.91 W/m² and the CO₂ concentration is 417 ppm, which exceeds safe limits. Maintaining 350 ppm would lead to lower warming and reduce risks.
- Industry,
- deforestation,
- agriculture,
- the burning of fossil fuels.
The aim of ensuring climate stability is to limit greenhouse gas concentrations to below 350 ppm CO₂. The key in terms of limiting the Earth system is:
- Reducing climate tipping points,
- preserving the biosphere and cryosphere,
- stabilising warming below 1.5 °C.
Currently, the radiative forcing is 2.91 W/m² and the CO₂ concentration is 417 ppm, which exceeds safe limits. Maintaining 350 ppm would lead to lower warming and reduce risks.
2. Biosphere integrity
The functional integrity of the biosphere, which is linked to the geosphere and regulates the state of the Earth, is key to understanding the state of the Earth’s biosphere. This integrity depends on:
Key findings include:
- Genetic diversity: the basis of the ecological complexity of the biosphere, shaped by natural selection and evolution. The current rate of species extinction exceeds 100 E/MSY.
- Planetary functioning: Estimated by proxies such as net primary production (NPP), which represents the flow of energy and matter into the biosphere.
Key findings include:
- Genetic diversity is vital for the resilience and adaptability of the biosphere. The aim is to keep species extinction rates below 10 E/MSY.
- Net primary production (NPP) is the basis for the functioning of the biosphere, measured by human appropriation of NPP (HANPP). This limit is greatly exceeded, pushing the biosphere into a high-risk zone.
3. Biogeochemical flows
Planetary constraints linked to biogeochemical fluxes include the phosphorus and nitrogen cycles, which are key for ecosystems. Human activities, in particular agriculture and industry, have had a major impact on the cycle. Excessive use of fertilisers causes pollution, algal blooms and ecosystem imbalances.
For phosphorus (P), the global limit is 11 Tg P/year from freshwater to the ocean, but current estimates (22 Tg P/year) exceed this limit. For nitrogen (N), the planetary limit is 62 Tg N per year, but current use (112 Tg N per year) exceeds this. Total anthropogenically fixed N uptake is about 190 Tg N per year, which exceeds the global N limit.
For phosphorus (P), the global limit is 11 Tg P/year from freshwater to the ocean, but current estimates (22 Tg P/year) exceed this limit. For nitrogen (N), the planetary limit is 62 Tg N per year, but current use (112 Tg N per year) exceeds this. Total anthropogenically fixed N uptake is about 190 Tg N per year, which exceeds the global N limit.
4. Freshwater change
The planetary limit for changes in the freshwater cycle covers the entire terrestrial water cycle.
Control variables measure deviations from pre-industrial conditions (1661-1860) on a global scale, with limits set at the 95th percentile of pre-industrial variability. Currently, 18% (blue water) and 16% (green water) of the world’s land area experiences wet or dry freshwater deviations, which represents a significant exceedance of the limit. These exceedances were already observed a century ago, highlighting the need for a precautionary approach (Richardson et al., 2023).
- Blue water: flowing water (surface water and groundwater)
- Green water: soil moisture in the root zone (water available to plants)
Control variables measure deviations from pre-industrial conditions (1661-1860) on a global scale, with limits set at the 95th percentile of pre-industrial variability. Currently, 18% (blue water) and 16% (green water) of the world’s land area experiences wet or dry freshwater deviations, which represents a significant exceedance of the limit. These exceedances were already observed a century ago, highlighting the need for a precautionary approach (Richardson et al., 2023).
5. Land use change
The planetary limit for land-use change focuses on major forest biomes:
The control variable measures the remaining forest area relative to the potential Holocene forest area. The latest land cover maps from 2019 show that the extent of deforestation, particularly in the Amazon tropical forest, has exceeded the planetary limit. Although estimation methods and technology are changing, the trend of decreasing global forest cover is evident.
- Tropical forests: 85% of the remaining forest area
- Temperate forests: 50% of the remaining forest area
- Boreal forests: 85 % of the remaining forest area
The control variable measures the remaining forest area relative to the potential Holocene forest area. The latest land cover maps from 2019 show that the extent of deforestation, particularly in the Amazon tropical forest, has exceeded the planetary limit. Although estimation methods and technology are changing, the trend of decreasing global forest cover is evident.
6. Ocean acidification
The control variable for this constraint is the concentration of carbonate ions in the surface layer of seawater, measured in units of Ωarag – the average saturation state of the surface ocean with aragonite. The original planetary constraint remains in place, which means that Ωarag must be at least 80% of the pre-industrial global average Ωarag of 3.44. Current estimates suggest that Ωarag is about 2.8, which is about 81% of the pre-industrial value, and puts ocean acidification at the edge of carrying capacity. The trend is worsening due to the steady increase in anthropogenic CO₂ emissions.
7. New entities and other pollutants
In the area of new entities, the planetary boundaries framework includes genuinely new anthropogenic inputs into the Earth’s system, such as:
These entities serve as geological markers of the Anthropocene. The framework’s purpose is to assess the stability and resilience of the Earth’s system, not the health of humans or ecosystems. The safe operating space includes the absence of these entities or the confirmation of their harmlessness before their introduction into the environment. The planetary boundary is 0% release of untested synthetic compounds into the Earth’s system. Despite challenges like incomplete data, the approach emphasizes the urgency of monitoring and regulating the release of new entities into the environment.
- synthetic chemicals (microplastics, endocrine disruptors, organic pollutants),
- anthropogenically mobilized radioactive substances (nuclear waste, nuclear weapons),
- genetically modified organisms.
These entities serve as geological markers of the Anthropocene. The framework’s purpose is to assess the stability and resilience of the Earth’s system, not the health of humans or ecosystems. The safe operating space includes the absence of these entities or the confirmation of their harmlessness before their introduction into the environment. The planetary boundary is 0% release of untested synthetic compounds into the Earth’s system. Despite challenges like incomplete data, the approach emphasizes the urgency of monitoring and regulating the release of new entities into the environment.
8. Anthropogenic Aerosol Load
Aerosols have various effects on the Earth’s system, including physical, biogeochemical, and biological impacts. The anthropogenic aerosol load has increased, with dust deposition globally doubling since 1750. Aerosol Optical Depth (AOD) is the control variable for aerosol load. Steffen and colleagues (2015) set a provisional regional planetary boundary for AOD, which is exceeded by South Asia.
Key findings:
A comprehensive understanding of aerosol impacts is crucial for refining the boundary value for aerosol load.
Key findings:
- Current global AOD: 0.14
- Regional differences in AOD: affect monsoons
- Proposed boundary: interhemispheric difference of 0.1, current value is 0.076
- Impacts: on precipitation and regional climate
A comprehensive understanding of aerosol impacts is crucial for refining the boundary value for aerosol load.
By promoting a global commitment to sustainability, we can work towards harmonious coexistence with our planet and ensure a resilient and thriving Earth for future generations.
Planetary boundaries
Discover various approaches to evaluating planetary boundaries and their consideration in the green transition.
The informational material includes detailed explanations of research approaches, analyses, and graphical representations.
The informational material includes detailed explanations of research approaches, analyses, and graphical representations.
