IB ESS HLTopic 8 — Human PopulationsPaper 1 & 2HL only~11 min read
Population Growth and Environmental Pressure
There are about 8.2 billion of us, and the number is still climbing. But population size on its own is a poor guide to environmental damage — what matters far more is how much each person consumes. One person in a wealthy country can put more strain on the planet than a dozen people elsewhere. This page is about measuring that strain, and about a model that asks whether we can meet everyone’s needs without breaking the systems that supply them.
📚 What you need to know
Global population is around 8.2 billion and is projected to reach roughly 10 billion by about 2075, then level off or slowly fall.
Projections depend most on fertility rates, which are genuinely uncertain, so any projection is a range not a number.
Environmental stress is the strain human activity puts on ecosystems through pollution, deforestation and resource use.
Biocapacity is the ability of an area to regenerate resources and absorb waste, measured in global hectares (gha).
A biocapacity deficit occurs when the ecological footprint is larger than the biocapacity available.
Biocapacity is very unevenly spread, so some countries live within their means while others import theirs.
The doughnut economics model puts a social foundation on the inside and an ecological ceiling on the outside, with a safe and just space between.
Where the population is heading
The world reached 8 billion in 2022 and sits at roughly 8.2 billion today. Most projections have growth continuing but slowing: around 10 billion by about 2075, and then either stabilising or beginning a slow decline by around 2125.
Four things decide which path we actually take.
Fertility rates — the biggest single unknown. Fertility has fallen faster than demographers expected in much of Asia and Latin America, and small changes compound over decades.
Mortality rates — further medical advances push these down, which raises the total.
Urbanisation — city families are consistently smaller, because children cost more and contribute less income.
Government policy — direct and indirect policies can nudge fertility either way, though usually less than governments hope.
Projections normally come as three scenarios: high, medium and low fertility. The medium one is treated as most likely, but the spread between high and low by 2100 is billions of people. If a question gives you a projection, say it is a scenario, not a forecast. That single sentence often carries an evaluation mark.
Footprint against biocapacity
To compare demand and supply we use one unit: the global hectare (gha), a standard hectare of land or sea with world-average productivity.
Ecological footprint is the demand: the area needed to supply everything a person uses and to absorb their waste, especially carbon dioxide.
Biocapacity is the supply: the area actually available and how productive it is.
Globally the average footprint is about 2.6 gha per person while biocapacity is around 1.5 gha per person. That is a deficit for the planet as a whole, and it is only possible because we are drawing down stocks — cutting forests faster than they regrow, and letting carbon dioxide build up rather than be absorbed.
Notice that the deficit countries are mostly the wealthy ones. High consumption, not large population, is what pushes the red bar up.
Why biocapacity is so unevenly spread
Biocapacity depends on how much productive land and sea a country has, divided by how many people share it. Large, forested, thinly populated countries such as Brazil, Canada and Sweden have plenty. Small desert states such as the UAE, and dense industrial economies such as China, have very little relative to what they use.
A country in deficit does not stop consuming. It imports the biocapacity instead, buying timber, soy, fish, metals and fuel from elsewhere. That is why a rich country can look clean and green at home while its footprint is being paid for in someone else’s forest. Many African nations have small footprints of their own yet face heavy resource extraction to supply wealthier markets.
The inequality point examiners want. The countries with the largest footprints are usually not the ones with the fastest population growth. Blaming environmental damage on population growth alone ignores who is actually doing the consuming.
WORKED EXAMPLE
A country of 12 million people has an ecological footprint of 5.4 gha per person and a biocapacity of 2.1 gha per person. Calculate the biocapacity balance per person and for the country, and comment on the result.
Step 1: balance per person2.1 − 5.4 = −3.3 gha per personA deficit of 3.3 gha per personStep 2: scale up to the whole country3.3 × 12 000 000 = 39 600 000 ghaA national deficit of 39.6 million ghaStep 3: comment5.4 ÷ 2.1 = 2.57, so the country uses about 2.6 times what its own land and sea can renew. The gap must be met by importing resources or by depleting stocks.
Negative balance = deficit. Keep the minus sign in your working; it is the difference between a reserve and a deficit.
Doughnut economics
The doughnut model asks a simple question: can everyone have a decent life without wrecking the systems that make life possible? It draws two boundaries.
The inner boundary is the social foundation: the minimum every person needs — food, water, health, education, housing, energy, income and work, political voice, gender equality, social equity, peace and justice.
The outer boundary is the ecological ceiling, made of the planetary boundaries: climate change, biodiversity loss, ocean acidification, land conversion, freshwater use, chemical pollution, nitrogen and phosphorus loading, air pollution and ozone depletion.
Fall through the inner boundary and you have a shortfall: people whose basic needs are not met. Push past the outer boundary and you have overshoot: damage to Earth systems. The ring between them is the safe and just space for humanity.
The two boundaries are independent. Fixing overshoot by cutting consumption for people already in shortfall would simply push them further in.
The clever part of this model is that it refuses to treat poverty and environmental damage as separate problems. Most environmental models only draw the outer limit. Adding an inner one forces you to ask who the environment is being protected for.
WORKED EXAMPLE
Country X has near-universal healthcare, schooling and clean water, but a footprint of 6.8 gha per person. Country Y has a footprint of 0.9 gha per person, but a third of its people lack safe water and 20% of children leave school before age 12. Describe each country’s position on the doughnut.
Step 1: Country X against the inner boundary
Basic needs are met, so it is above the social foundation — no shortfall.
Step 2: Country X against the outer boundary
6.8 gha per person is far above what the planet can supply per person.
Country X is in overshoot but not shortfallStep 3: Country Y
A footprint of 0.9 gha is inside the ecological ceiling, so no overshoot. But unmet water and education needs put it below the social foundation.
Country Y is in shortfall but not overshootThe fix is different in each case: X must cut consumption, Y must raise living standards without copying X’s footprint.
Term
What it means
How to spot it in data
Ecological footprint
The area needed to supply one person and absorb their waste
A gha per person figure for demand
Biocapacity
The area available and how productive it is
A gha per person figure for supply
Biocapacity deficit
Footprint larger than biocapacity
Negative balance; resources imported
Biocapacity reserve
Biocapacity larger than footprint
Positive balance; often exports resources
Overshoot
Human activity beyond a planetary boundary
Outside the ecological ceiling on the doughnut
Shortfall
Basic human needs not being met
Inside the social foundation on the doughnut
💡 Exam tip
Learn the definitions of biocapacity, biocapacity deficit, social foundation and planetary boundaries. They are frequent one-mark questions.
Always say per person when quoting a footprint or biocapacity. Without it the number is meaningless.
Separate population size from consumption per person. Answers that treat them as the same thing lose the evaluation marks.
Name at least one deficit country and one reserve country. Two words each is enough.
For the doughnut, use the words shortfall and overshoot precisely. Inside is shortfall; outside is overshoot.
If you are given projection data, mention uncertainty in fertility rates. It is the single best evaluative comment available here.
⚠ Common mix-ups
Swapping footprint and biocapacity. Footprint is what we take; biocapacity is what the land can give.
Reading a deficit as “this country is poor”. Deficits are most common in wealthy, high-consumption countries.
Putting overshoot inside the doughnut. Overshoot is beyond the outer ring.
Saying the population will keep growing forever. Most projections have it levelling off this century.
Assuming a large population always means a large footprint. A country of 200 million with low consumption may have a smaller total footprint than one of 30 million with very high consumption.
Treating the doughnut as a measurement. It is a framework for thinking, not a set of measured values.
Up next: Dependency Ratios and Population Momentum — two calculations that explain why the age structure of a country matters as much as its size.
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