Rapid population growth has stressed Earth's systems by increasing demand for food, water, energy and land while accelerating waste production, pollution and biodiversity loss. In IB ESS, this is HL-only content in subtopic 8.1 Human populations.
A human population can be modelled as a system: births and immigration are inputs, while deaths and emigration are outputs. When inputs remain greater than outputs, population increases. If total consumption rises faster than ecosystems can regenerate resources or absorb waste, human activity becomes unsustainable.
| Pressure from population growth | Stress on Earth's systems |
|---|---|
| Greater food demand | Agricultural expansion causes habitat loss, soil degradation and increased fertilizer use; nutrient runoff may cause eutrophication. |
| Greater freshwater demand | Aquifers and rivers may be depleted, reducing water security and damaging aquatic ecosystems. |
| Greater energy demand | Fossil-fuel combustion increases greenhouse gas emissions, strengthening the enhanced greenhouse effect. |
| Urban expansion | Land conversion fragments habitats, increases surface runoff and creates more air and solid-waste pollution. |
| Greater resource consumption | Extraction reduces natural capital and may exceed ecological regeneration rates. |
These pressures interact through feedback. For example, deforestation provides agricultural land but reduces carbon storage, contributing to climate change; climate change can then lower crop yields and water availability. Rapid growth may therefore reduce system resilience and increase the risk of crossing tipping points.
The Aral Sea illustrates interconnected pressures: large-scale irrigation for agriculture reduced river inputs, causing severe ecosystem decline and harming fishing communities. However, the common misconception is that population growth alone causes environmental degradation. Environmental impact also depends on per-capita consumption, technology, governance and resource distribution; smaller affluent populations may have much larger ecological footprints per person.
Environmental justice is also important because marginalized groups often experience the greatest pollution, scarcity and displacement despite consuming fewer resources.
Exam technique: For an “explain” question, construct clear causal chains from population growth to resource demand and environmental consequences. For “discuss” or “evaluate,” include population size alongside consumption, technology, governance, perspectives and a named example before reaching a supported conclusion.
