Planetary Boundaries Science
A complete framework for understanding how we can maintain the safe operating space for humanity.
What are Planetary Boundaries?
Planetary Boundaries are scientific benchmarks that establish the limits within which humanity can safely operate, to maintain the Earth’s environmental stability, resilience and life-support functions.
These Boundaries define the critical points beyond which human activity could cause irreversible damage to our planet, and fundamentally threaten 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 we can maintain the safe operating space for human civilization to continue.
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.
Earth's safe operating space
The high-risk zone where safe conditions from Earth's past have already been exceeded
Safe Conditions
Boundary Transgressed
Increasing Risk
High Risk
Boundary Transgressed
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, is a growing barrier to socio-economic progress and a threat to livelihoods.
Changes in Vegetation Productivity
Extreme weather, insect infestations, wildires 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
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.
Decreased crop yields due to droughts and heatwaves are straining food security, while 2.2 billion people lack safely managed drinking water, and 3.5 billion lack adequate sanitation, contributing to 1.4 million deaths annually.
Furthermore, 2 billion tons of waste are generated each year, with 45% mismanaged, leading to hazardous pollution and nearly 7 million deaths linked to air pollution.
In 2023, 600 million people were already living outside the optimal human climate niche, underscoring 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
What is a safe operating space?
A safe operating space is an Earth system state that allows humanity to develop and thrive for generations to come.
Human civilization has only existed for approximately 10,000 years of the 4.56bn years of Earth’s history (a tiny 0.0002%). It is a result of the relative stability in the Earth system after the last ice ages. We are now shifting away from this state at an alarming rate.
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Only 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 as shown in these graphs.
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Planetary Boundaries vs Tipping Points
Planetary Boundaries are intended to be a global indicator of our safe operating space.
They define the “global domain” of natural systems or processes.
They are not intended to be measures of dangerous thresholds in specific natural systems such as the polar ice caps, or ocean currents. These thresholds are better defined by tipping points science. Breaching our Planetary Boundaries can cause us to cross tipping points leading to irreversible change.
How we measure Planetary Boundaries
Each of the nine Planetary Boundary processes has specific control variables that indicate their status. For example:
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Carbon dioxide concentration is a control variable for climate change
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The proportion of remaining original forest cover measures land use change
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The extinction rate is used as a proxy for genetic diversity in assessing biosphere integrity.
Each of the nine Planetary Boundary processes has specific control variables that indicate their status. For example:
These variables are monitored using a wide variety of methods depending on the temporal and spatial scale required.
The framework enables comparisons of these variables across all Boundaries, and helps scientists pinpoint where human activities are pushing Earth's systems beyond safe limits.
Scientific research is ongoing to expand the number of control variables, and strengthen the framework.
Interconnectedness and a Whole Earth Approach
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 solution. It is crucial that PB assessments and decision making follow a Whole Earth approach.
As human activity is the biggest driver of change in Planetary Boundaries, it is crucial that we adopt a Whole Earth Approach to decision making in all areas of our societies and economies.
Top stories on planetary boundaries
The Planetary Health Check is an initiative supported by:
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