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You may think you live on a planet, but really you live on a gigantic farm, one occasionally broken up by cities, forests and the oceans. Some 40% of the world’s land surface is used for the purposes of keeping all 7 billion of us fed – albeit some of us, of course, more than others. And the vast majority of that land – about 30% of the word’s total ice-free surface – is used not to raise grains, fruits and vegetables that are directly fed to human beings, but to support the chickens, pigs and cattle that we eventually eat.

Livestock production – which includes meat, milk and eggs – contributes 40% of global agricultural gross domestic product, provides income for more than 1.3 billion people and uses one-third of the world’s fresh water. There may be no other single human activity that has a bigger impact on the planet than the raising of livestock. But as a new study out today in the journal
Proceedings of the National Academy of Sciences (PNAS) shows, there is tremendous variation in how we raise livestock around the world – and major differences in what that means for the earth and for us.

Researchers from the International Livestock Research Institute in Kenya, the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia and the International Institute for Applied Systems Analysis (IIASA) in Austria produced a comprehensive assessment of the livestock industry around the world, in developed nations where factory farming is common and in developing nations where livestock are more likely to graze on grasslands. They dug up some striking statistics that underscore just how much meat production varies from region to region.