xxii Sustainable Agriculture and Food
all these relationships will remain linear in the future, and that gains will continue
at the previous rates (Tilman, 1999). This would assume a continuing supply of
these factors and inputs, and that the environmental costs of their use will be
small. There is also growing evidence to suggest that this approach to agricultural
growth has reached critical environmental limits, and that the aggregate costs in
terms of lost or forgone benefits from environmental services are too great for the
world to bear (Ruttan, 1999; MEA, 2005). The costs of these environmental prob-
lems are often called externalities, as they do not appear in any formal accounting
systems. Yet many agricultural systems themselves are now suffering because key
natural assets that they require to be plentiful are being undermined or dimin-
ished.
Agricultural systems in all parts of the world will have to make many improve-
ments. In some, the challenge is to increase food production to solve immediate
problems of hunger. In others, the focus will be more on adjustments that main-
tain food production whilst increasing the flow of environmental goods and serv-
ices. World population is set to continue to increase until about 2040–2050, and
then is likely to stabilize or fall because of changes in fertility patterns. The high
fertility projection by the UN (2005) is unlikely to arise, as shifts towards lower
fertility have already occurred in many countries worldwide, and so there are very
real prospects of world population eventually falling over the one to two centuries
Source: FAO (2005)
Figure 2c Relationship between world agricultural land area and world plant food
production (1961–2002)