Limits on human growth at Higher Level: The same ideas as SL, with different real cases: smallpox, the Aral Sea, Singapore's water and the UN's projection.
Practise this as you read
- Link each technology to the limiting factor it removed.
- Weigh natural limits against people's choices.
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The brakes came off: The numbers of other species are held in check by limiting factors. Humans have removed most of theirs, so the human population has grown for over 200 years.
The points to remember
- Natural predators were removed: weapons, farming and living in towns keep people safe.
- Medicine, vaccines and clean water cut deaths from disease, so the death rate fell.
- Technology raised the food supply: fertilisers, irrigation and new crop varieties.
- Trade and transport move food and resources to where people need them.
- With fewer limits, the population grew exponentially: 1 billion in 1800, 8 billion in 2022.
Remember it as: No predators, less disease, more food: the brakes came off.
Real example: smallpox killed about 300 million people in the 20th century; vaccination eradicated it by 1980, so it no longer limits human numbers.
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More people, each using more resources, put pressure on ecosystems. Removing the natural limits has a cost.
What happens to ecosystems
- Habitat loss: forests and wetlands are cleared for farms, towns and roads.
- Overharvesting: fish, timber and wild animals are taken faster than they renew.
- Pollution and climate change from farming, industry and fossil fuels.
- Invasive species spread with trade and travel.
- Biodiversity loss: extinctions run far above the background extinction rate.
- Degradation of soil, water and fish stocks can become a new limiting factor on people.
Remember it as: More people, more pressure: habitats, harvests, pollution, climate, invasives.
Growth harms ecosystems
- Forests are cleared for farms and towns.
- Extinctions run far above the natural rate.
But the harm can be reduced
- Protected areas and breeding programmes.
- Mountain gorillas rose to over 1000 by 2018.
Weigh both sides: Growth usually reduces biodiversity, and conservation can slow the loss, but overall the loss is still rising.
Real example: the Aral Sea shrank to about a tenth of its size after its rivers were used to irrigate cotton; its fishing industry collapsed, and salty dust from the dry seabed now blows onto farmland.
Two old views disagree about whether people can keep outgrowing their limits.
Malthus
- Population grows faster than food.
- Famine, disease and war will limit it.
Boserup
- Need drives new ideas.
- Technology raises the food supply.
What technology can and cannot do
- Food: GM crops, vertical farms and fertilisers raise yields.
- Water: desalination, water treatment and reuse.
- Energy and pollution: renewable energy, catalytic converters, scrubbers and carbon capture.
- Births: contraception lets families choose to have fewer children.
- But: it is costly, poorer countries may not afford it, and it can create new problems.
Remember it as: Malthus: food runs out. Boserup: need drives new ideas.
Real example: Singapore treats used water to drinking quality, as NEWater, and desalinates seawater, so an island with little land to catch rain can support about 6 million people.
Technology can move a problem: Fertilisers raise yields, but they wash into rivers and harm the wildlife there.
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Nature's brakes or people's choices?: Future growth may be limited by natural factors returning, or by people choosing to have fewer children, as the demographic transition model predicts.
The points to remember
- Natural limiting factors could return: water shortages, poor harvests, disease and a changing climate.
- Population policies act directly: family planning, or limits on the number of children.
- Development acts indirectly: education for girls and better health care lower birth rates.
- Birth rates are already falling in most countries as they develop.
- The UN projects the world population will peak at about 10.3 billion in the 2080s.
Remember it as: Nature's brakes or people's choices?
Real example: in South Korea, women now have fewer than one child each on average, the lowest rate in the world, with no law forcing it.
How this comes up: Paper 2, Section B (c) [9]: a 'to what extent' or 'discuss' essay on human population growth and its limits.
The world's population passed 8 billion in 2022.
To what extent are natural limiting factors more likely than population policies to limit global human population growth in the future?
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