More than a third of Earth鈥檚 ice-free land area is now being used for farming. Europe, south Asia and the eastern US have the greatest proportion of arable land, while South America, China, the western US and tropical Africa have the largest proportion of pasture (see Map).
Navin Ramankutty from McGill University in Montreal, Canada, and colleagues compared agricultural inventories from all countries with satellite land-cover data for the same areas, and wrote a computer program to recognise pasture and crop land.
Examining satellite data from 2000, they estimate that 28 million square kilometres (22 per cent) of ice-free land surface is covered in pasture and 15 million square km (12 per cent) is used to grow crops. Their 10 km-resolution maps provide the most detailed and accurate figures to date (Global Biogeochemical Cycles, ).
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The real figure is likely to be higher still. 鈥淲e have likely missed a large extent of very small farms with subsistence agriculture,鈥� says Ramankutty. What鈥檚 more, the method overlooks pasture underneath trees and struggles with forest crops such as palm oil.
Nonetheless, observations are helping with assessments of the impact of agriculture on the environment. Farmland is expanding in Latin America and south-east Asia due to the demand for soya and palm oil, and shrinking in Europe and China. 鈥淥n balance, the percentage of agricultural land looks set to increase. Biofuels especially may add to the pressure,鈥� says Ramankutty.
