The world produces plenty of food – over 5,000 calories a day per person. Nevertheless, the sustainability of our food supply is one of the central problems facing the world. As countries become wealthier an increasing fraction of the world’s agricultural output is fed to animals, which typically turn eight calories of food into only one calorie of meat. Can the world’s total food supply expand fast enough to accommodate the increasing percentage of calories going to feed animals? A new paper suggests that a 2050 world that has global agricultural productivity as good as the US today, but also copies the US’s dietary patterns, would need nearly double the global land area devoted to arable crops in 2050. This is impossible to achieve without large scale further destruction of vital forests.[1] Over the past four decades, a growing fraction of world food supply has been diverted to meat animals. Nevertheless, the typical person has access to about 2,750 calories today, up from 2,250 forty years ago. This increase has occurred as a result combination of four interlinked factors.

1) The amount of land used for growing food has increased by about 35%. This increase has, of course, partly come from the destruction of forests, pushing many gigatonnes of carbon into the atmosphere.

2) Yields per hectare have risen, and are still rising, at between 1 and 2% per year.

3) The population has grown sharply

4) Lastly, diets have changed, implying a need to produce more primary calories in the form of crops for use by animals.

The paper has a very interesting and elegant way of expressing the impact of each of these forces. It estimates the impact on agricultural land area of each factor, showing how the extra cropland was used. Total land area devoted to arable crops rose by nearly 270 million hectares from 840 to about 1,110 million hectares.

Force at work	Impact on global arable land area

Increase in population	+682 million hectares
Increase in animal products in human diet	+239 million hectares
Improved agricultural technology, including irrigation	-654 million hectares
Net land extra land area devoted to arable crops	+267 million hectares

We know that global population is likely to increase sharply between now and 2050. The paper assumes that the number rises by about 2bn to around 9bn. (Many people will regard this as improbable, seeing a figure of around 10bn as more likely.) If the rest of world ends up with US style dietary habits, expressed in terms of animal products consumption and overall calorie intake, but also is as good as the US is today at producing food, then 9bn people of 2050 will need almost double today’s arable land area. If the global patterns are of Western European dietary and agricultural productivity, then the increase is about 70%.

The FAO says that arable land area can be increased by 5% from today’s levels without further loss of forest. The implication is therefore that the world is set on a collision course as rising prosperity meets insufficient land area to meet demand for animal products. The price of food will continue to rise sharply, probably pushing large numbers back into malnutrition. Or the world continues to cut down its forests, increasing carbon losses and also affecting local and regional rainfall patterns. Both routes are terrifying.

[1] Global changes in diets and the consequences for land requirements for food. Thomas Kastner et al, Proceedings of the National Academy of Sciences, April 2012