Planetary Boundaries Science
A complete framework for understanding how we can maintain the safe operating space for humanity.
Planetary Boundary Status
Six of the nine Boundaries are now operating beyond safe limits, two more than in 2015. The state of our Earth system has continued to deteriorate since the last assessment in 2023.
Planetary Boundary process inside Earth's safe operating space
Planetary Boundary process outside Earth's safe operating space
Safe Conditions
Boundary Transgressed
Increasing Risk
High Risk
Boundary Transgressed
What are Planetary Boundaries?
Planetary Boundaries are the scientifically established limits within which humanity can safely operate, maintaining the Earth’s environmental stability, resilience and life-support functions. The Boundaries are the safe limits for human pressure on the nine critical processes which together maintain a stable and resilient Earth. Each process is measured using one or more variables, effectively quantifying the damage that human actions are doing to the Earth.
Human activity is the main reason these Earth processes cross their boundaries. We are now risking causing irreversible damage to our planet, and fundamentally threatening our societies and economies.
Planetary Boundaries are interdependent, meaning that if we cross one Boundary, we will affect others, or even cause them to cross out of the safe operating space. We cannot consider Planetary Boundaries in isolation in any decision making on sustainability. Only by respecting all nine boundaries can we maintain the safe operating space for human civilization.
Early Warning Signs
Planetary Boundaries (PBs) are essential safeguards for the stability, resilience, and life-support functions of the Earth system. Transgressing these boundaries endangers at least one of these functions. Additionally, transgressing or even approaching a PB can lead to significant and often unpredictable environmental impacts.
There are several well-known symptoms of crossing Planetary Boundaries, including:
Extreme Weather
More frequent and severe droughts and heatwaves, along with increased instances of extreme precipitation and flooding.
Extreme Events
Compound drought-wildfire events now affect more than one third of global vegetated areas. Global coral bleaching events are increasing.
Water scarcity
Driven by multiple factors particularly over-use in irrigation and land use changes, it is a growing barrier to socio-economic progress and a threat to livelihoods.
Changes in Vegetation Productivity
Extreme weather, insect infestations, wildfires and excessive use of fertilizers all harm plant health, and impact food production.
Increase in Waste
The accumulation of human-made substances such as plastics is continually increasing.
Declining global carbon sinks
Human activities and climate change are rapidly degrading the carbon sequestration capacity of terrestrial ecosystems.
Profound Consequences
Breaching the Planetary Boundaries is already having profound consequences for humanity.
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Over the past two decades, climate change has been linked to 7,348 major disasters, resulting in 1.23 million deaths and $2.97 trillion in economic losses
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2.2 billion people lack safely managed drinking water, and 3.5 billion lack adequate sanitation, contributing to 1.4 million deaths annually.
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In 2023, 600 million people were already living outside the optimal human climate niche. Even in conservative models, it is predicted that by 2090, more than 2 billion people will be exposed to unprecedented heat. This underscores the urgent need to address these issues for the sake of both planetary health and human survival.
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Global Map of Countries that Declared Drought Emergencies in 2022-2023.
During 2022-2023, widespread drought conditions affected various regions, including North America, Europe, Asia, and Africa, and were often accompanied by major wildfires. This underscores the severe impact of prolonged dry conditions on different parts of the world.
Why do we cross Planetary Boundaries?
Human activity is the biggest contributor to our breaching of Planetary Boundaries. The most notable activities include:
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Burning fossil fuels causing increased greenhouse gas emissions
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Large-scale animal farming leading to increased greenhouse gas emissions and biodiversity loss
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Deforestation for animal and crop farming and urban expansion
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Increased water use for industry and urban expansion
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Pollution from synthetic chemicals such as plastics and radioactive materials
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Introduction of invasive species
The Great Acceleration
The last 200 years of human activity has forced the Earth system outside the safe operating space, driving changes at an unprecedented rate, and not just in global temperatures. This is called the Great Acceleration.
These graphs illustrate the dramatic socio-economic and Earth system trends in recent decades. The left-hand (red) side highlights the exponential rise in human activities, including population growth, real GDP, and energy use. The right-hand side reveals the corresponding impact on Earth system indicators such as carbon dioxide levels, surface temperature, and ocean acidification.
What is a safe operating space?
An Earth system state that enables humanity to develop and thrive for generations to come. It encompasses environmental conditions similar to those of the Holocene epoch, which began around 11,700 years ago. During this time, humans developed agriculture and modern civilizations. The Safe Operating Space ensures that crucial Earth system processes remain within boundaries that support global stability, resilience and life-support functions.
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Humanity's Journey on Earth
Over the past 3 million years, the Earth’s temperature has fluctuated within a narrow "corridor of life": between +2°C at the warmest, down to around -5°C during the deep Ice Age. But then, the conditions stabilized and became more predictable. For over 10,000 years, humanity lived with an average temperature of 14°C ± 0.5°C, which enabled our modern world to develop. By crossing several Planetary Boundaries, including the one for Climate Change, this period has ended. We are on track for 2-3°C of warming, and are entering a new and dangerous terrain in which a still-growing world population must thrive.
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We risk losing so much resilience in the Earth system that we trigger a planetary shift, causing an unstoppable drift from the Holocene state we are familiar with, towards a Hot House Earth state.
An alarming diagnosis for planetary health
We have a planetary health crisis, and science is clear: the patient, our home planet Earth, is in critical condition. The prognosis is dire as we continue to push past the Planetary Boundaries and deepen and accelerate the planetary crisis, threatening human health and wellbeing, economic prosperity, social stability, and equity.
A patient in a critical condition needs regular monitoring. The Planetary Health Check fulfills this role by monitoring all nine Planetary Boundaries and providing decision makers in public and private sectors with improved data, to accelerate and scale the transformations towards a safe and just landing for humanity within the planetary boundaries.
The "blood sample test" of overall Planetary Health on top, showing that Earth is on Red Alert, with a negative trend deeper into the high-risk zone. This Planetary diagnosis is based on the nine PB parameters, shown along the same "blood sample scheme" ranging from green (Safe operating space), yellow (danger zone set by the uncertainty range in science) and transitioning into a red embers scale of rising risk (dark red equals high risk zone).
Planetary Boundaries and Tipping Points
Planetary Boundaries are a global indicator of our safe operating space for humanity. Tipping points are points of critical danger to the Earth system.
One of the primary reasons for setting Planetary Boundaries is to avoid crossing tipping points - dangerous thresholds in specific natural systems such as the polar ice caps, or ocean currents. Crossing tipping points results in irreversible changes in these systems that would have catastrophic outcomes for billions of people.
Interconnectedness and a Whole Earth Approach
Just like for the Planet itself, interconnectedness is fundamental to the Planetary Boundaries framework. Changes in one Boundary (whether positive or negative) affect other boundaries. This is both a risk and an opportunity when it comes to finding solutions. It is crucial that Planetary Boundary assessments and decision making follow a Whole Earth approach.
Changes in one Boundary (whether positive or negative) affect other boundaries. This is both a risk and an opportunity as positive changes can also have knock-on effects.
As human activity is the biggest driver of change in Planetary Boundaries, it is crucial that we follow a Whole Earth approach to decision making in all areas of our societies and economies.
Research is ongoing to delve deeper into the complex net of “drivers of transgression” for each Boundary, and the complex net of interconnections between Boundaries.
The Complex Net of Planetary Boundary Processes
To illustrate some parts of this causal network, two simplified, but representative examples are below.
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Biogeochemical Flows: How Nitrogen and Phosphorus Fertilizer Diminish the Oceans’ Biodiversity & Fuel Climate Change
Nitrogen and phosphorus fertilizers are widely used to enhance crop yields, but their excessive use causes these nutrients to leach into freshwater and ultimately marine systems. This leads to algal and cyanobacterial blooms which depletes the oxygen in the water. This causes fish and other species to die in large numbers, affecting Biodiversity, and the decay of the dead biomass releases CO2, further fueling Climate change and Ocean Acidification.
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Land System Change: How Deforestation Creates a Vicious Cycle of Forest Loss, Fueling Freshwater Overuse, Biodiversity Loss & Climate Change
Deforestation due to agriculture or urban expansion causes loss of biodiversity, disrupts water flows from soil to air, and the transfer of particles that are part of cloud formation, ultimately affecting rain patterns. A decrease in cloud cover drives increased temperatures, and increased exposure to wind causes drying soils, erosion and a higher likelihood of wildfires. Reduction in rainfall also drives increased use of Freshwater for irrigation. Finally, destruction of forests reduces the Earth’s carbon sinks, further accelerating Climate Change.