Resources, stocks and flows
A natural resource is anything from nature that people use. Resources are developed in stages: first they are found (exploration), then taken out (extraction), then processed and used. Each stage needs money, technology and people.
- Non-renewable (stocks): coal, oil, gas, metal ores. They formed over millions of years. Every tonne used is gone.
- Renewable (flows): water, forests, fish, soil, wind, sun. They refill, but only at a certain speed. If we use them faster than that speed, they also run out.
Sustainability
Sustainable use meets today's needs without reducing what future people can use. It has three sides: environment, economy and society.
Ecological footprint
Your ecological footprint is the area of land and water needed to grow your food, give you materials and absorb your waste. Measured in global hectares (gha). The world average is about 2.6 gha per person, but Earth can only supply about 1.6 gha each. Rich countries have much bigger footprints than poor ones.
The tragedy of the commons and overuse
A common is a resource shared by many and owned by none: the open ocean, a village grazing ground, the air, an underground aquifer. Each user thinks: "If I take a bit more, I gain the whole extra amount, and the loss is shared by everyone." When all users think this way, the common collapses. This is the tragedy of the commons.
Overfishing
About a third of the world's fish stocks are now fished faster than they can recover. Effects: fish get smaller, food chains break, coastal jobs vanish, and bycatch (unwanted animals caught by mistake) kills dolphins, turtles and sharks. Bottom trawling scrapes the seabed.
Fixes
- Quotas: a limit on catch, often set near the maximum sustainable yield (the largest catch that can be taken every year without shrinking the stock).
- Closed seasons and marine protected areas.
- Permits, fees, or community rules made by the users themselves.
Water security and irrigation
Water security means enough safe water for people, farms, industry and nature, now and in future. Threats: growing population, pollution, overpumped groundwater, climate change and shared rivers that cross many countries.
Irrigation methods
| Method | How it works | Water reaching crop |
|---|---|---|
| Flood | Fill the whole field | ≈ 50% |
| Furrow | Water runs in channels between rows | ≈ 65% |
| Sprinkler | Sprays water like rain | ≈ 75% |
| Drip | Pipes drip water at each plant's roots | ≈ 90% |
Too much irrigation can cause waterlogging and salinisation (salt left behind in the soil when water evaporates).
Other ways to increase water security
Rainwater harvesting, check dams, fixing leaks, recycling waste water, desalination (removing salt from seawater; uses a lot of energy), and large transfer schemes or dams (useful, but they can flood land and move people).
Urban runoff
Roofs and roads are hard surfaces, so rain rushes off carrying oil and rubbish, and causes floods. Fixes: permeable pavements, rain gardens, green roofs, and keeping wetlands.
Energy security
Energy security means a reliable, affordable supply of energy. About 80% of the world's energy still comes from oil, coal and gas. Risks include running out, price shocks, wars or politics blocking supply, and climate change from burning fossil fuels.
- Energy mix: the share of each source a country uses. A wider mix is safer.
- Import dependence: India imports about 85% of its oil, so world prices affect it strongly.
- Solutions: renewables (solar, wind, hydro), nuclear power, efficiency (getting the same work from less energy), strategic fuel reserves and better power grids.
Land use: farming, forests and mining
Forestry
Clearcutting removes every tree in an area. It is cheap, but causes soil erosion, flooding, loss of habitat and more CO2. Sustainable forestry uses selective cutting, replanting, and protecting old forest and river banks.
Pest control
Chemical pesticides kill pests fast, but pests become resistant, and poisons harm bees, fish and people. Integrated pest management (IPM) uses many methods: crop rotation, natural predators (like ladybirds that eat aphids), traps, resistant crop varieties, and chemicals only as a last step.
Meat production
Feedlots (many animals kept close together and fed grain) produce cheap meat but use lots of water and grain and create waste and disease risk. Free-range grazing uses more land and can cause overgrazing if there are too many animals. Eating less meat lowers the footprint.
Sustainable agriculture
Crop rotation, intercropping, contour ploughing and terraces on slopes, no-till farming, compost and green manure, and windbreaks.
Aquaculture
Fish farming takes pressure off wild fish and produces food efficiently, but can pollute water, spread disease to wild fish, and destroy mangroves to build ponds.
Mining
Mining gives metals and fuels, but strip mining removes whole landscapes, mine waste can poison rivers (acid mine drainage), and dust harms health. Laws require reclamation: refilling, replanting and cleaning the land afterwards.
Resource futures and case studies
Will we run out? Views differ:
- Pessimists (following Malthus) say population will outgrow resources.
- Optimists (following Boserup) say pressure pushes people to invent new methods.
Future pathways include a circular economy (reuse and recycle everything), new technology, fair trade agreements, and international rules for shared rivers and seas.
Short case studies
- Aral Sea (Central Asia): rivers diverted for cotton irrigation shrank the lake by about 90%.
- Grand Banks cod (Canada): overfishing collapsed the stock in 1992; a fishing ban followed.
- Indian groundwater: free electricity for pumps led to overuse; drip schemes and village water budgets are now spreading.
Try it
In the 3D free-play step, start with 5 boats and add boats one at a time. Write the yearly catch for each number. Plot a graph of boats (x) against catch (y). Where is the top of the curve? That is the maximum sustainable yield. At home: measure how much water your family uses in one day (count buckets), and list two ways to cut it by 10%.
Key formulas and definitions
- Resource security: enough supply, reliably, at an affordable price
- Renewable resource: refills naturally at a limited rate
- Non-renewable resource: a fixed stock that runs down when used
- Tragedy of the commons: shared resource ruined because each user takes a little extra
- Maximum sustainable yield (MSY): the largest catch that can be taken each year without shrinking the stock
- Ecological footprint: land and water area needed to support a person, in global hectares
- Salinisation: salt building up in soil after irrigation water evaporates
- Integrated pest management: using many pest controls, with chemicals last
Worked examples
1. A farm needs 4,500 litres of water to reach its crop each day. How much water must be supplied by flood irrigation (50% reaches the crop) and by drip irrigation (90%)?
Flood: 4,500 ÷ 0.5 = 9,000 L. Drip: 4,500 ÷ 0.9 = 5,000 L. Drip saves 4,000 L a day.
2. A fish stock grows by 12 tonnes per year at its present size. What happens if boats catch 20 tonnes per year?
Each year the stock falls by 20 − 12 = 8 tonnes. As it shrinks, it grows even less, so the decline speeds up and can end in collapse.
3. Explain why a village grazing field can be overgrazed even though every family is sensible.
Each family gains the full benefit of adding one more cow, but the damage to the grass is shared by everyone. So each family adds animals, and together they ruin the field. This is the tragedy of the commons.
4. World average footprint ≈ 2.6 gha per person; Earth can supply ≈ 1.6 gha per person. How many Earths would we need?
2.6 ÷ 1.6 ≈ 1.6 Earths. We are using resources about 60% faster than they renew.
Common mistakes
- Thinking renewable means unlimited. Fish, forests and groundwater run out if used faster than they refill.
- Believing more boats always means more fish. Past the maximum sustainable yield, more effort gives a smaller catch.
- Saying aquaculture is always good for the environment. It can pollute water and destroy mangroves if badly managed.
- Treating energy security only as running out of fuel. Price shocks, imports and politics matter just as much.