"Urban agriculture can be defined shortly as the growing of plants and the raising of animals within and around cities. The most striking feature of urban agriculture, which distinguishes it from rural agriculture, is that it is integrated into the urban economic and ecological system: urban agriculture is embedded in -and interacting with- the urban ecosystem. Such linkages include the use of urban residents as labourers, use of typical urban resources (like organic waste as compost and urban wastewater for irrigation), direct links with urban consumers, direct impacts on urban ecology (positive and negative), being part of the urban food system, competing for land with other urban functions, being influenced by urban policies and plans, etc. Urban agriculture is not a relict of the past that will fade away (urban agriculture increases when the city grows) nor brought to the city by rural immigrants that will lose their rural habits over time. It is an integral part of the urban system.
It was the development of agriculture some 10,000 years ago that made cities possible and it has sustained their growth over the millennia. This sustenance is becoming problematic in an era when a majority of humans are for the first time residing in urban areas—at the same time as the species is dealing with global climate change. The principal threat to the human species from this climate change is to agriculture. The UN projects a global population in 2050 of 9 billion, 70 percent of whom will live in cities. This population will require about 70 percent more food that the 2009 population. Meanwhile, expanding cities coupled with the floods and droughts expected from global climate change will reduce the store of arable land. The upshot of these changes is that our species must enhance its food production on a large scale, and do so in a sustainable fashion.
On the one hand, the potential for urban agriculture to play a substantial role in urban poverty and food insecurity reduction should not be overemphasized, as its share in income and overall agricultural production is often quite limited. On the other hand, though, its role should also not be too easily dismissed, particularly in much of Africa and in all those countries in which agriculture provides a substantial share of income for the urban poor, and for those groups of households to which it constitutes an important source of livelihoods."