Biofuels - The Oxford Topic of Food, Politics, and Society - page 181

11%; pastureland, 27%; forestland, 32%; urban, 9%; and other 21%. Most of the “other” land
area (21%) is unsuitable for crops, pasture, and/or forests because the soil is too infertile
or shallow to support plant growth, or the climate and region are too harsh, cold, dry,
steep, stony, or wet ( FAO 2013). Most of the land suitable for crops is already in use.
Because the human population has continued to increase rapidly, there has been
an expansion of land area occupied by diverse human activities and human habita-
tion, which has dramatically reduced cropland and pastureland. Much vital cropland
and pastureland has been covered by transportation systems and urbanization. In the
United States, about 0.4 hectares (1 acre) of land per person is covered with urbaniza-
tion and roads (USCB 2008). In 1960, when the world population numbered only 3 bil-
lion, approximately 0.5 hectares (ha) was available per person for the production of a
diverse, nutritious diet of plant and animal products (Giampietro and Pimentel 1994).
Based on agricultural estimates for the United States in the 1960s, 0.5 ha includes land
for human food and animal products essential for a healthy diet (Pimentel and Pimentel
2003). China's recent explosion in development provides an example of a rapid decline
in the availability of per capita cropland (Pimentel and Wen 2004). The current available
cropland in China is only 0.08 ha per capita. This relatively small amount of cropland
provides most of the people in China with a predominantly (over 90%) vegetarian diet,
which requires less energy, land, and biomass than the typical American diet.
In addition to land, water is a vital controlling factor in crop production (Gleick 1996;
Homer-Dixon 2012). Enormous quantities of water are required for crop production.
During the growing season for corn of a little over three months, a corn crop utilizes
more than 6.5 million liters of water per hectare (Pimentel and Pimentel 2008). The pro-
duction of nine tons per hectare (t/ha) of corn requires about 7 million liters of water
(about 700,000 gallons of water per acre) (Pimentel et al. 2004). The production of rice
requires even more water, or about 11 million liters of water per hectare.
Irrigation provides much of the water for world food production. The 17% of the
cropland worldwide that is irrigated provides about 40% of total food produced each
year (FAO 2003). Unfortunately, irrigated land is declining per capita at about 10% per
decade (Pimentel and Pimentel 2008). Worldwide, about 70% of all freshwater con-
sumed is consumed by irrigation, and in the United States about 80% of the water con-
sumed is consumed by the 15% of the crops that are irrigated (Pimentel and Pimentel
2008). Global arid conditions are spreading and intensifying because of global warm-
ing (Aroca and Ruiz-Lozano 2009), and water use is increasing for activities other than
agriculture, causing irrigation to decline. A major concern is that world irrigation water
is projected to decline further because of global climate change (Cline 2007).
Energy Resources and Use
Since the industrial revolution of the 1850s, the rate of energy use from all sources has
been growing even faster than world population. For example, from 1970 to 1995, energy