The general perception that livestock is a major contributor to global warming resulted mainly from the FAO publication, Livestock's Long Shadow, in 2006, which indicated that livestock is responsible for 18% of the world's greenhouse gas (GHG) emissions. This figure has since been proved to be an overestimation, since it includes deforestation and other indirect contributions. The most recent figure is in the order of 5% - 10%. Although only ruminants can convert the world's high-fibre vegetation into high-quality protein sources for human consumption, ruminant production systems are targeted as they are perceived to produce large quantities of GHG. Livestock is also accused of using large quantities of water, an allegation that is based on questionable assumptions and the perception that all sources of food production require a similar and equal quantity and quality of water. In the case of ruminants, extensive systems are usually found to have a lower per-area carbon footprint than grain-fed systems, but a higher footprint if expressed in terms of kg product. Feedlots maximize efficiency of meat production, resulting in a lower carbon footprint, whereas organic production systems consume more energy and have a bigger carbon footprint than conventional production systems. Cows on pastures produce more methane than cows on high concentrate diets. In South Africa, as in most of the countries in the sub-tropics, livestock production is the only option on about 70% of the agricultural land, since the marginal soils and rainfall do not allow for crop production and the utilization of green water. An effective way to reduce the carbon and water footprint of livestock is to decrease livestock numbers and increase production per animal, thereby improving their efficiency.