Food security depends on supply and access

1. Food security exists when a population has reliable access to enough safe, nutritious and affordable food for a healthy diet.
2. A factor lowers food security if it reduces the amount or variety of food, interrupts supply or raises prices beyond what people can afford.
3. Biological explanations should connect the factor to crop or livestock yield and then to availability, variety, price or access.

Population growth increases demand

1. A larger human population requires more total energy, protein, vitamins, minerals and water from the food system.
2. If food production grows more slowly than the population, the amount available per person falls.
3. More farmland and irrigation may be needed, which increases competition for land and fresh water and can damage habitats or soils.
4. Shortages raise prices and make reliable access hardest for people with low incomes.

Meat and fish use more resources

1. Rising meat consumption increases animal farming, so more crops, land and water are used to feed livestock rather than people directly.
2. Energy and biomass are lost between trophic levels, so feeding crops to animals produces less human food energy than eating suitable crops directly.
3. Livestock also require housing, temperature control, medicines and waste management, which increase agricultural inputs and production costs.
4. Greater demand for fish can cause overfishing, reducing breeding populations and making future catches smaller.
5. Fish farming can increase supply, but it requires feed and careful control of disease, waste and escapees to remain sustainable.

Pests and pathogens cut yields

1. Pests eat crops, damage stored food or compete with livestock, so less usable food reaches people.
2. Plant pathogens reduce photosynthesis, growth or reproduction, while animal pathogens reduce growth, fertility and survival.
3. A new pathogen can spread quickly if crops or livestock lack resistance, especially where many genetically similar individuals are kept together.
4. Diseased animals may need to be isolated or culled, and infected crops may need to be destroyed, which reduces supply immediately.
5. Pesticides, medicines, resistant varieties and biosecurity can limit losses, but they add costs and may become less effective as resistance evolves.

Environmental change reduces harvests

1. Human greenhouse-gas emissions increase global temperatures and alter rainfall patterns, raising the risk of drought, flooding and heat stress.
2. Drought closes stomata and limits photosynthesis, while flooding reduces oxygen around roots and can kill crop plants.
3. Warmer conditions can shift the ranges of pests, pathogens and pollinators, exposing farms to new diseases or reducing pollination.
4. Sea-level rise can make coastal soils and irrigation water saltier, reducing water uptake and crop growth.
5. More frequent crop failures make supply less reliable and increase price variation.

Biofuels compete with food crops

1. Land used to grow maize, sugar cane or oilseed for biofuel cannot produce food at the same time.
2. Diverting edible crops into fuel reduces the food entering markets and can raise prices.
3. Clearing new land for fuel crops can remove habitats, release stored carbon and reduce soil quality, which threatens future food production.
4. Waste plant material can make biofuel with less direct competition for fertile farmland, but collection and processing still require energy and money.

Inputs can limit production

1. Fertilisers replace mineral ions removed in harvests, pesticides reduce losses, and fuel and machinery allow large areas to be farmed.
2. Feed, seed, water, labour, medicines, fertiliser, pesticides, energy and machinery all add to the cost of producing food.
3. If input prices rise, farmers may use less of them, which can reduce yield, or pass the cost to consumers through higher food prices.
4. Poorer farmers may be unable to buy high-quality seed, irrigation or disease control, so pests, drought or nutrient shortage cause larger losses.
5. Overusing inputs can also damage long-term production through soil degradation, water pollution, pesticide resistance and loss of pollinators.

Sustainable choices protect future supply

1. Sustainable food production maintains soil, water supplies, pollinators, wild fish stocks and genetic diversity so production can continue in future years.
2. Crop rotation, resistant varieties, efficient irrigation, careful fertiliser use and managed fishing quotas can reduce losses without exhausting the resource base.
3. A method is not sustainable if it raises today's yield by causing soil erosion, resistant pests, collapsed fish stocks or permanent habitat loss.
4. The best response to a food-security question weighs increased present supply against cost, environmental damage and the ability to keep producing food.