**5. Peak hydrocarbons**

The great abundance of easily accessed fossil fuels and the correspondingly low price of energy that fueled the Green Revolution were temporary phenomena. Consequently, impending maxima in production of oil and coal, and eventually natural gas, combined with the dependence of global food production on fossil fuels and novel demands for agricultural production of biofuels, pose a daunting challenge for food security.

Agriculture around the world depends to varying degrees on gasoline and diesel for mechanized farm machinery, for transportation of supplies to farm and ranch and deliveries of products to market, and for off-grid energy to power irrigation pumps. It depends critically on natural gas to create ammonia-based nitrogen fertilizers. In many areas, especially in developed countries, agriculture depends on coal-fired electricity for irrigation, food processing, preservation, and cooking (see sector for "Other Input" in developed countries in Figure 5). In addition, fossil fuel inputs also contribute to energyintensive mining of phosphorus, a critical nutrient with limited mineable resources (Elser & Bennett, 2011). The fossil oil, natural gas, and coal that power modern society, in particular contemporary global agriculture, were deposited by geological processes over millions of years. Large-scale human exploitation of coal has occurred for little more than 200 years; for oil and gas the timescale is little more than 100 years. Evidence is accumulating that production of these non-renewable resources will reach a maximum in the coming decades during which humankind must meet the challenge of food security. Peak production could come much sooner.
