Food Security

The world population has risen from about 3 billion in 1960 to nearly 8 billion today, and the United Nations expects it to approach 10 billion by about 2050.

Better medicine, vaccination and clean water mean that fewer people die young and more people live longer, so numbers rise even when families get smaller.

The area of farmland cannot grow without destroying forests and other habitats, so each hectare of land has to feed more and more people.

Population is rising fastest in some of the poorest regions, where food production is already hardest to improve.

In wealthier countries many people eat more meat, milk and cheese than they once did, and the same change is now happening in fast-growing economies.

When we eat an animal, we are one trophic level further along the food chain, and much of the energy in the animal's feed is lost as heat and in waste. Producing meat therefore needs far more land and crops than eating the plants directly.

A large share of the world's cereals and soya is grown to feed livestock instead of people, so a diet rich in meat takes food and land from other people.

Wealthier people also expect a wide choice of foods all year round, which relies on transport and on growing crops in other countries.

Insects such as locusts and fall armyworm eat leaves and stems and can destroy a whole crop in days, which is why a swarm of desert locusts is so dangerous for local food supplies.

Fungi, bacteria and viruses cause plant diseases such as wheat rust, which lower the yield or kill the plants altogether.

Global trade and travel carry pests and pathogens to new countries where the crops have no resistance, and a warming climate lets them survive in places that were once too cold.

Pests and pathogens evolve. Strains that survive a pesticide or fungicide reproduce, so a chemical that worked for years may stop working.

Rising temperatures, droughts and floods damage crops and shorten the growing season. A single drought can ruin a harvest, and crops that grew well in one region may not grow there in future.

Heavy rain, ploughing and clearing trees wash topsoil away, and growing the same crop for years removes minerals, so the soil becomes less fertile.

Irrigation takes water from rivers and from underground, and in dry regions the supply is running low.

Sea water floods low-lying farmland and makes the soil salty, so crops cannot be grown there.

Sustainable means meeting people's needs now without stopping future generations from meeting theirs. Taking too much water, wearing out the soil or catching too many fish are all unsustainable.

These are the things a farmer has to buy or provide, such as seed, fertiliser, pesticide, animal feed, fuel, machinery and water. Each costs money.

If fertiliser, fuel or feed becomes more expensive, farmers can afford less of it, so yields fall and food prices rise. Poorer farmers are hit hardest and may be unable to buy enough to grow a good crop.

Fertiliser washed into rivers can cause eutrophication, and pesticides can kill harmless insects and reduce biodiversity, so intensive farming can harm the ecosystems that farming depends on.

Say whether it rises or falls, quote two values with their units and years, and say whether it is steady or speeding up.

Work out the change, divide by the starting value and multiply by 100. For example, a rise from 3.0 to 7.8 billion is a 160% increase.

Divide the total food produced by the population. If this falls, food production is not keeping up with population growth.

Totals can hide differences between countries, and a correlation between two sets of data does not by itself prove that one causes the other.