Why "global change"?

The core takes a global, systems view: people, climate and resources change together, and the power to cause and to cope with change is unevenly spread across places.

• Population: how many people, where, and how age structures are shifting.
• Climate: the causes of change and the very different vulnerability and resilience of places.
• Resources: rising per-capita demand for water, food and energy, and the security of supply.

Command focus: Paper 2 rewards data skills plus a balanced, located, evaluative argument.

Distribution, density & megacities

People are spread very unevenly. Density = people ÷ area. Increasingly, population concentrates in megacities (over 10 million) through urbanisation. Distribution is shaped by:

• Physical factors — relief, climate, water and soils.
• Human factors — jobs, cities, transport, history and policy.

Scale: a country that looks "sparse" nationally can still contain an extremely dense megacity — always specify the scale you mean.

Where do people cluster?

Births, deaths & natural increase

A population changes through births, deaths and migration. The natural increase rate (from births and deaths only) is:

Because steady percentage growth compounds, we estimate doubling time with the rule of 70:

Your turn — natural increase

Your turn — doubling time

Ageing structures & dependency

The Demographic Transition Model shows birth and death rates falling as a country develops. Many high-income countries now face an ageing structure. A key measure is the dependency ratio:

Ageing challenge: a large 65+ share raises the dependency ratio and strains pensions and healthcare — pro-natalist policy and later retirement are common responses.

Your turn — dependency ratio

Migration & population policy

Migration redistributes people, driven by push factors (poverty, conflict, hazards) and pull factors (jobs, safety, services). Governments steer change with policy:

• Anti-natalist — reduce birth rates (family-planning programmes).
• Pro-natalist — raise birth rates in ageing societies.
• Migration policy — points systems, work visas, integration or restriction.

Possibilities & power: the "gender and change" strand stresses that empowering women — through education and work — is one of the strongest drivers of falling fertility.

Which core unit?

Tap a term, then tap the Global Change unit it belongs to.

Global climate — causes & vulnerability

The enhanced greenhouse effect from rising CO₂, methane and other gases is warming the planet, shifting rainfall, raising sea level and intensifying some extremes.

Vulnerability is how exposed and sensitive a place is, and how little it can cope. It depends on physical exposure and on wealth, governance and infrastructure.

Climate justice: the places that have emitted the least are often the most vulnerable — a core question of power.

Same hazard, different outcome

Adaptation vs mitigation

Resilience is the capacity to absorb and recover from change. Two response strategies — know the difference:

• Mitigation — tackling the cause: cutting greenhouse-gas emissions (renewables, carbon pricing, reforestation).
• Adaptation — living with the consequences: sea walls, drought-resistant crops, early-warning systems.

Possibilities: realistic futures combine both — mitigation slows the change, adaptation manages what can no longer be avoided.

Adapt or mitigate?

Global resource consumption

As populations grow and become wealthier, per-capita demand for water, food and energy rises. We track change with index numbers, which rescale data so a base year = 100:

The ecological footprint compares demand on nature with the Earth's biocapacity; living beyond biocapacity is an "ecological overshoot".

Your turn — index number

Match the term to its meaning

Tap a description on the left, then its matching term on the right.

Resource security & the nexus

Resource security means reliable, affordable access to enough water, food and energy. These three are linked — the water–food–energy nexus — so stress in one cascades into the others. Water stress, for example, is measured as the share of available water withdrawn:

Power & possibilities: the "circular economy" and the neo-Malthusian vs Boserup (technological optimism) debate are exactly what an "evaluate" question rewards.

Reading the nexus

The big ideas to know

You've covered the key ideas across the three units of the Global Change core. Press Finish to see your score.