How much land can ten billion people spare for nature

Abstract

If people keep multiplying and farmers keep farming as they do now, farmers will soon need to grow their crops on twice as large an area as what they use today.1 Doubling the popu lation without changing the way we farm would expand the crop land from its present tenth of the world's land to about a fifth. More than any other factor, the success farmers have in feeding more people per hectare (ha) will govern what humanity is able to spare for Nature. I capitalize Nature here and throughout to indicate a specific definition, namely, the features and products of the earth itself, as contrasted with those of human civilization. My essay presumes a population of ten billion people because that seems to be the round number in sight. The billions may level off at ten, or they may grow further.2 In either case, we must contemplate ten billion. I presume also that humanity should spare lots of land for Nature. Proponents of the sparing of land reason about portfolio, money, and ethics. They argue that sparing land for Nature brings security by assuring a portfolio of biological diversity. They assert that Nature saves our money through her free ecosystem services.3 At bottom, however, is the ethical argument that survives quib bling over the utility of genes in a jungle or whether a marsh purifies water more cheaply than does a sewage plant. Although most religions emphasize humanity, even Genesis declares, Let the waters bring forth swarms of living creatures, and let birds fly