IB ESS SL1.3 SustainabilityPaper 1 & 2Core idea~13 min read
Frameworks for Sustainable Thinking
Indicators tell you a number. They do not tell you whether the number is bad. For that you need a framework: something that says here is the line, here is what happens if you cross it. Two of them dominate modern sustainability thinking, and they fit together neatly.
📚 What you need to know
The planetary boundaries model sets limits for nine Earth system processes, defining a safe operating space for humanity.
Crossing a boundary raises the risk of large, abrupt and possibly irreversible change — a tipping point.
Several boundaries have already been crossed, including climate change, biosphere integrity, biogeochemical flows and land-system change.
Doughnut economics (Kate Raworth) adds a social floor to that ceiling.
The social foundation is the minimum everyone needs; the ecological ceiling is what the planet can take.
The ring between them is the safe and just space for humanity.
Both are models, so all the strengths and limitations from 1.2 apply to them.
Planetary boundaries
Proposed by a team of Earth system scientists led by Johan Rockström in 2009, this framework asks a blunt question: which processes keep the Earth in the stable state that has allowed civilisation to develop, and how far can we push each one before that stability breaks?
Definition
The safe operating space is the range within which all nine Earth system processes can be pushed without an unacceptable risk of abrupt, large-scale, irreversible change.
Boundary
What it tracks
Climate change
Greenhouse gas concentration and the extra energy trapped by the atmosphere
Biosphere integrity
Rate of species extinction and loss of ecosystem function
Biogeochemical flows
Nitrogen and phosphorus added to soils and water, largely from fertiliser
Land-system change
Conversion of forest and other habitat to farmland and cities
Freshwater use
Water taken from rivers and groundwater, and changes to soil moisture
Ocean acidification
Carbon dioxide dissolving into seawater and lowering its pH
Atmospheric aerosols
Particles in the air that alter rainfall patterns and health
Ozone depletion
Thinning of the stratospheric ozone layer
Novel entities
Plastics, synthetic chemicals and other substances new to the Earth system
The bars are qualitative. What matters is which side of the dashed line each process sits on, not the exact height.
Why the model is powerful
It turns “the environment” into nine specific processes that can be measured separately.
It uses the language of thresholds and tipping points from 1.2, so it fits the systems view exactly.
It makes clear that some problems interact — crossing the climate boundary makes staying inside the biosphere integrity boundary much harder.
Where it gets criticised
The exact position of each boundary is uncertain and has been revised as science improves.
Some processes, such as aerosols, do not have one global threshold at all — they are regional.
It is a global model, so it says nothing about who is responsible or who suffers first.
It sets a ceiling but says nothing about human needs, which is exactly the gap the next framework fills.
Doughnut economics
The economist Kate Raworth took the planetary boundaries ceiling and added a floor underneath it. The result looks like a doughnut, and the shape is the argument.
Most countries today miss on both sides at once: they overshoot the ceiling and still leave people below the foundation.
Part of the doughnut
What it is
What crossing it means
Ecological ceiling
The nine planetary boundaries
Overshoot — environmental damage and risk of tipping points
Shortfall — people are denied the basics of a decent life
The ring between
The safe and just space for humanity
Everyone’s needs met within the planet’s limits
The whole point of the doughnut is that it refuses the trade-off. It does not say “protect the environment or help people”. It says any answer that fails either test is the wrong answer, and then asks what an economy designed to land in the ring would look like.
Comparing the two frameworks
Planetary boundaries
Doughnut economics
What it sets
An upper limit only
An upper limit and a lower limit
Based on
Earth system science
Planetary boundaries plus social priorities from the SDGs
Strength
Specific, measurable processes with scientific thresholds
Combines environmental and social goals in one picture
Limitation
Silent on human needs and on fairness
The social floor is a value judgement, so the position of the line is arguable
🧠
Easy way to remember it
Ceiling is above you — the planet’s limit. Foundation is below you — the human minimum. Fall through the floor and people suffer; push through the roof and the planet does.
Do not forget they are models. Everything from the models page in 1.2 applies here. Both frameworks simplify enormously, both depend on the quality of the data behind them, and both involve choices about where to draw a line. That does not make them useless — it makes them useful and provisional at the same time, which is what a good model should be.
Worked examples
WE 1
Explain the planetary boundaries model
Outline the planetary boundaries model and explain what happens when a boundary is crossed. (4 marks)
Point 1: what it is
It identifies nine Earth system processes and sets a limit for each, defining a safe operating space for humanity.
Point 2: examples
They include climate change, biosphere integrity, biogeochemical flows and land-system change.
Point 3: crossing a boundary
Crossing one raises the risk of large, abrupt and possibly irreversible change — the system may pass a tipping point.
Point 4: the current position
Several boundaries have already been crossed, and they interact, so crossing one makes others harder to stay within.
Nine limits, a safe space inside them, and rising risk outsideuse the phrase “safe operating space” and link it to tipping points from 1.2
WE 2
Explain the doughnut
Explain how the doughnut economics model combines environmental and social goals. (3 marks)
Point 1: the ceiling
The outer ring is the ecological ceiling, taken from the planetary boundaries. Going beyond it causes overshoot and environmental damage.
Point 2: the foundation
The inner ring is the social foundation: the minimum of food, water, health, education, energy and voice that everyone needs. Falling below it is shortfall.
Point 3: the space between
The ring between them is the safe and just space, where human needs are met without breaching environmental limits.
Not environment or people — both, or the answer is wrongname both rings correctly; ceiling and foundation are the terms that earn marks
WE 3
Evaluate a framework
Evaluate the usefulness of the planetary boundaries model for guiding environmental policy. (4 marks)
Strength 1
It breaks a vague problem into nine measurable processes, each with a threshold, so progress can be tracked.
Strength 2
It communicates risk clearly and is grounded in Earth system science.
Limitation 1
The exact position of each boundary is uncertain and has been revised, and some processes are regional rather than global.
Limitation 2
It is silent on human needs and on who is responsible, so it cannot guide questions of fairness on its own.
Judgement
Very useful for setting environmental limits, but needs a social framework such as the doughnut alongside it.
A good ceiling, but a ceiling is not a whole houseusing one framework to criticise the other is exactly the kind of linking examiners reward
💡 Exam tips
Learn at least five of the nine boundaries by name, and which ones have been crossed.
Use safe operating space, ecological ceiling, social foundation and safe and just space precisely.
Link boundaries to tipping points from 1.2 — it is the same idea at planetary scale.
Say who developed each model: Rockström and colleagues for boundaries, Raworth for the doughnut.
Remember both are models, so the strengths and limitations of models apply.
The doughnut is the fix for the boundaries model’s blind spot — say so.
⚠ Common mistakes
Saying crossing a boundary causes instant collapse. It raises the risk of abrupt change; it is not a switch.
Mixing up ceiling and foundation. Ceiling is environmental, foundation is social.
Thinking the doughnut replaces planetary boundaries. It contains them as its outer ring.
Treating boundary positions as exact. They carry real scientific uncertainty.
Forgetting the interactions. The boundaries affect one another.
Ignoring the shortfall side. Many countries fail the social floor and the ecological ceiling at the same time.
Up next: Rethinking Economic Models — if the doughnut shows the target, the last question is what kind of economy could actually land in it.
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