What food security means

1. Food security is reliable access at all times to enough safe, nutritious and affordable food for a whole population.
2. Four conditions have to be met together: the food must be available, people must be able to access it, they must be able to afford it, and the supply must be stable from one year to the next.
3. Food insecurity is the state in which one or more of those conditions fails, so people cannot rely on getting the food they need.
4. A country does not have to grow all of its own food to be food secure, because food can be imported, but it does need a supply it can depend on.
5. The United Kingdom produces a little over half of the food it eats and imports the rest, so a disruption to trade affects its food security as much as a poor harvest at home does.
6. Food security is judged at several scales, from a single household, to a country, to the whole world, and a country with a good average supply can still contain households that are food insecure.

A growing human population

1. The human population is rising, so the total mass of food that has to be produced each year rises with it.
2. The rise comes mainly from a falling death rate, as medicine, clean water and sanitation improve, while the birth rate stays high in many countries.
3. The area of land suitable for farming is not rising at the same rate, so the amount of food produced per hectare, the yield, has to rise instead.
4. Clearing more land to farm is possible but removes habitats, so it trades food production against the wildlife and soil that farming itself depends on.
5. More people also need more fresh water, and irrigation competes with drinking water and with water for industry.

Changing diets in wealthier populations

1. As average incomes rise, people eat less cereal and more meat, fish and dairy produce.
2. Producing food from animals is far less efficient than producing it from plants, because only a small fraction of the energy in the feed a farm animal eats ends up in the meat or milk that people eat.
3. The rest of that energy is lost in respiration, in movement, as heat, and in material that is not eaten, so several kilograms of plant material are needed for every kilogram of meat produced.
4. Land used to grow animal feed is therefore land that is not growing food for people directly, and a shift towards meat raises the total area of farmland a population needs.
5. Livestock also need large volumes of water, both to drink and to grow their feed, which adds to the demand on water supplies.
6. Wealthier populations expect foods out of season as well, so crops are flown or shipped in from other climates, which raises the fuel cost of the food supply.

New pests and pathogens

1. A pest is an organism that feeds on or damages a crop or a farm animal, and a pathogen is a microorganism that causes disease in one.
2. Both lower yield, because a damaged or diseased plant photosynthesises less and puts less of its biomass into the parts that are harvested.
3. International trade and travel move pests and pathogens between continents, so a species arrives in a region where local varieties have no resistance to it and no natural predator controls it.
4. Fields planted with a single variety are especially vulnerable, because every plant in the field carries the same alleles and so has the same susceptibility.
5. Insect pests cause damage twice over, by eating the crop and by carrying plant viruses from one plant to the next as they feed.
6. Disease in livestock can force whole herds or flocks to be culled, which removes that food supply for several years while numbers are rebuilt.
7. Warmer winters allow insect pests to survive from one season to the next, so their populations start each spring from a larger number.

Environmental change

1. Rising average temperatures shift the regions in which a crop grows well, so land that reliably produced a crop may stop doing so while land further north becomes usable.
2. Drought lowers the water available to a crop, the stomata close to conserve water, carbon dioxide can no longer diffuse into the leaf, and the rate of photosynthesis falls.
3. Flooding fills the air spaces in soil with water, so root cells cannot obtain enough oxygen for aerobic respiration and the roots die.
4. Extreme weather at the wrong point in the growing season is particularly damaging, because a storm at flowering or at harvest can destroy a crop that was growing well.
5. Salt water flooding coastal farmland lowers the water potential of the soil solution, so roots cannot take up water by osmosis and the land becomes unusable.
6. Environmental change also moves pests and pathogens into new areas, which is why its effects on food security are larger than the direct effect on plant growth alone.

Cost and sustainability of farming inputs

1. Yield is the amount of useful product harvested from a given area of crop or from a given number of animals, and raising it is how farmers meet rising demand from a fixed area of land.
2. Raising yield depends on inputs, which include fertilisers, pesticides, fuel, irrigation water, animal feed, seed and machinery.
3. Manufacturing nitrogen fertiliser uses a large amount of energy, so its price rises and falls with the price of fuel, and fuel is also needed for every tractor, pump and lorry on the farm.
4. When input costs rise faster than the price a farmer is paid, the farmer applies less fertiliser or plants a smaller area, and the amount of food produced falls.
5. Sustainability means meeting the needs of people today without preventing future generations from meeting their own needs.
6. Irrigating from underground water taken out faster than rainfall replaces it is not sustainable, because the supply eventually fails.
7. Ploughing bare soil and growing the same crop repeatedly without returning organic matter causes soil erosion and a loss of soil fertility, so yields fall in later years.
8. A method that raises yield this season while destroying the soil, water or pollinating insects that next season depends on lowers food security in the long term.