Increasing preference for beef magnifies human impact on world's food web.

Bonhommeau et al.’s report, “Eating up the world’s food web and the human trophic level” (1), provides a valuable perspective on the role of human food consumption within the global ecosystem. However, the ranking of human beings at a similar trophic level as other animals downplays the effects that humans have on the Earth in comparison with other species. The sheer volume of food consumed by humans and our growing preference for inefficient food sources cause us to have increasingly disproportionate impacts on the global ecosystem in relation to other species, even of the same trophic level. The importance of dietary preference is exemplified by differences between China and the United States. China’s human tropic level (HTL) increased from 2.1 in 1989 to 2.2 in 2009. This increase in HTL was driven by a more than doubling of pork consumption in China over the past two decades. Over the same period, total beef consumption in China increased sixfold, from ∼1 million tons in 1989 to >6 million tons in 2009 (2). Beef is an extremely inefficient food source; the land area required to produce a kilogram is beef is >2.5 times greater than required for pork and >3 times greater than for poultry (3, 4). As such, the area of land required to meet China’s food demands is growing at a faster rate than required based on population growth and increasing HTL alone. Roughly three times as much land area was required to meet China’s demand for meat in 2009 as in 1989 [∼470,000 km in 1989 vs. 1,380,000 km in 2009; estimates based on annual consumption of beef, pork, and poultry (2) and global average land requirements for production (3)]. Over this period, China’s population increased by ∼18% and per capita meat consumption increased by 135%. Together, these two factors account for roughly 90% of the increase in required land area. An additional 71,000 km of increased land demand is because of a doubling in the relative consumption of beef (beef constituted 4% of meat consumed in 1989 and 9% in 2009). In the United States, population size increased by 22% and per capita meat consumption increased by 6% (2). These two factors alone would have resulted in a 30% increase in the area of land required for meat production. However, in contrast to China, the United States has decreased relative consumption of beef (beef accounted for 40% of meat consumed in 1989 and 33% in 2009). Consequently, the total land area required to fulfill the meat demands of the United States increased by only 21%. Despite a relatively low HTL (1), humans have a dominant role in the world’s food web, appropriating ∼10% of total net primary productivity for food production purposes alone (1, 5). This amount will almost invariably increase in the future because of growing population sizes and concurrent increases in the HTL; this pressure on the Earth’s systems can be further magnified by a rapidly growing preference for beef and other inefficient food sources.