Introduction: http://www.sciencemag.org/cgi/content/short/327/5967/797

In just 40 years world population is expected to reach 9 billion, up from slightly less than 7 billion now. Providing secure food supplies for this many people is an unprecedented challenge. Yet, we have limited amounts of land and water to grow more food, and environmental degradation already results from intensive cropping systems that depend on large-scale application of synthetic fertilizers. We also see shifting patterns of temperature and rainfall through climate change that affect crop productivity. Providing a secure food supply for billions more people, even as about a billion live without sufficient protein, remains one of humanity's key challenges. 

In a special issue, Science Magazine examines the obstacles and opportunities ahead: A couple of articles from the special:

Abstract: "Continuing population and consumption growth will mean that the global demand for food will increase for at least another 40 years. Growing competition for land, water, and energy, in addition to the overexploitation of fisheries, will affect our ability to produce food, as will the urgent requirement to reduce the impact of the food system on the environment. The effects of climate change are a further threat. But the world can produce more food and can ensure that it is used more efficiently and equitably. A multifaceted and linked global strategy is needed to ensure sustainable and equitable food security, different components of which are explored here.."

Abstract: "Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century's demands for food, feed, fiber, and fuel while reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows."