Agriculture - WITNESS

The crop and livestock calculates the land surface required to feed humanity (and the amount of crops that can be used for energy).

It addresses the challenge of producing enough food on limited land for a large population by testing different diets and computing the necessary agricultural land area. Food categories are grouped as per the following table, with different effects of global warming for each (depending on climate damage such as drought, flooding or increased crops water needs), as well as different GHG emissions.

Red meat	White meat	Milk	Eggs	Rice and Maize	cereals	Fruit and vegetables	Fish	Other
Beef herd, dairy herd, Lamb & Mutton	Pig, poultry	Milk	Eggs	Rice, Maize	Barely, Oatmeal, Wheat and Rye	Apples, Bananas, Berries and grapes, Brassicas, Cassava, Cirtus fruit, Onions and leeks, other fruit, other pulses, other vegetables, peas, potatoes, root vegetables, tomatoes	Fish(farmed)	Sugar, cheese, coffee, chocolate, oils, soybean, wine

Once the food is produced, part of it (30% globally, assuming harvest to retail 17% and retail to consumption 13%) is not send to the population model to represent the waste that exists between production and consumption.

Model limitations (more detailed in the detailed documentation which link is provided above) include

• The model does not allow a modification of the global kcal amount of the diet. This kcal amount is set by the initial diet, and will remain the same.
• The model does not test the feasibility of the diet change. For example, convert 100% of red meat or white meat in one year is allowed in the model, even if it is probably not realistic.
• The model considers a global average diet, and does not include change depending on country or habits.
• The land use to produce food are assumed to be able to produce any type of food, with no regards of average weather or climate conditions. For example equatorial or temperate climate may have different affinity with food production.
• The CH4 emissions for livestock are voluntarily underestimated to keep global ghg estimates accurate