Jeff Sachs says that if world population doesn't stabilize relatively soon, we're headed for trouble:
Transgressing Planetary Boundaries, by Jeff Sachs, Scientific American: We are eating ourselves out of house and home. ... The green revolution that made grain production soar gave humanity some breathing space, but the continuing rise in population and demand for meat production is exhausting that buffer. ...
Food production accounts for a third of all greenhouse gas emissions... Through the clearing of forestland, food production is also responsible for much of the loss of biodiversity. Chemical fertilizers cause massive depositions of nitrogen and phosphorus, which now destroy estuaries in hundreds of river systems and threaten ocean chemistry. Roughly 70 percent of worldwide water use goes to food production, which is implicated in groundwater depletion and ecologically destructive freshwater consumption from California to the Indo-Gangetic Plain to Central Asia to northern China.
The green revolution, in short, has not negated the dangerous side effects of a burgeoning human population, which are bound to increase as the population exceeds seven billion around 2012 and continues to grow as forecast toward nine billion by 2046. ...
It is not enough to produce more food; we must also simultaneously stabilize the global population and reduce the ecological consequences of food production—a triple challenge. A rapid voluntary reduction in fertility rates in the poor countries, brought about by more access to family planning, higher child survival and education for girls, could stabilize the population at around eight billion by 2050.
Payments to poor communities to resist deforestation could save species habitats. No-till farming and other methods can preserve soils and biodiversity. More efficient fertilizer use can reduce the transport of excessive nitrogen and phosphorus. Better irrigation and seed varieties can conserve water and reduce other ecological pressures. And a diet shifted away from eating beef would conserve ecosystems while improving human health.
Those changes will require a tremendous public-private effort that is yet to be mobilized. ... The window of opportunity to achieve sustainable development is closing.