Driven mainly by population and economic growth, total world food consumption is expected to increase over 50% by 2030 and may double by 2050 (Bruinsma, 2003; Barker et al., 2007). Most of the increase in food production in the next decades is expected to occur through further intensification of current cropping systems rather than through opening of new land into agricultural production (Gregory et al., 2002). Intensification of cropping systems has been a highly successful strategy for increasing food production. The best example is the well-known success of the Green Revolution, where the adoption of modern varieties, irrigation, fertilizers and agrochemicals resulted in dramatic increases in food production. However, this strategy also resulted in unexpected environmental consequences, one of them being the emissions of greenhouse gases (GHGs) into the atmosphere (Matson et al., 1998). Therefore, future strategies that promote further intensification of agriculture should aim at the development of sustainable cropping systems that not only consider increasing food production but that also look at minimizing environmental impact.

The concentration of GHGs (CO2, CH4 and N2O and halocarbons) has increased since the pre-industrial revolution years due to human activities. The atmospheric

© CAB International 2010. Climate Change and Crop Production (ed. M.P. Reynolds)

concentration of CO2 has increased from 280 ppm in 1750 to 3279 in 2005, and N2O has increased from 270 ppb to 319 ppb during the same time period, while CH4 abundance in 2005 of about 1774 ppb is more than double its pre-industrial value of 750 ppb (Solomon et al., 2007). These gases absorb light in the infrared regions and thus trap thermal radiation, which in turn results in global warming. The global warming potential (GWP) is a useful metric for comparing the potential climate impact of the emissions of different GHGs by expressing CH4 and N2O in CO2 equivalents. The GWP of N2O is 298 times, while CH4 is 25 times that of CO2 in a 100-year time horizon (Forster, 2007; Solomon et al., 2007).

At present, 40% of the Earth's land surface is managed for cropland and pasture (Foley et al., 2005). The most important cropping systems globally, in terms of meeting future food demand, are those based on the staple crops, rice, wheat and maize. Rice and maize are each grown on more than 155 million ha (FAOSTAT, 2009). In addition, rice is the staple food of the largest number of people on Earth. The geographic distribution of rice production gives particular significance to Asia where 90% of the world's rice is produced and consumed (Fig. 9.1). Maize is produced mainly in the Americas, followed by Asia and then Africa (Fig. 9.2). Maize is important as a staple crop (mainly in developing countries) but it is also important as animal feed and, increasingly, as biofuel. Wheat is the most widely grown crop, covering more than 215 million ha around the world, with Asia covering close to 50% of the world wheat area (FAOSTAT, 2009; Fig. 9.3).

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