for National Geographic News
Food production takes up almost half of the planet's land surface and threatens to consume the fertile land that still remains, scientists warn.
The global impact of farming on the environment is revealed in new maps, which show that 40 percent of the Earth's land is now given over to agriculture.
University of Wisconsin-Madison scientists compiled the maps using satellite images and crop and livestock production data from countries around the world. The team presented their picture of global land use this week at a meeting of the American Geophysical Union in San Francisco.
"The satellite data tells us where cultivation is occurring with good spatial accuracy, while the census data is able to tell us what is being grown there," said Navin Ramankutty, a land-use researcher with Wisconsin-Madison's Center for Sustainability and the Global Environment (SAGE).
The maps suggest that an area roughly the size of South America is used for crop production, while even more land7.9 to 8.9 billion acres (3.2 to 3.6 billion hectares)is being used to raise livestock.
And with the world's population growing rapidly, the pressure is on farmers to find new land to cultivate, the study team says.
"How can we continue to produce food from the land while preventing negative environmental consequences, such as deforestation, water pollution, and soil erosion?" Ramankutty said.
The researchers also used past land-use data to create maps showing how agriculture has spread over the centuries. In 1700, for example, just 7 percent of the world's land was used for farming.
Figures from the Food and Agriculture Organization of the United Nations suggest that total farmland increased by 12.4 million acres (5 million hectares) annually between 1992 and 2002.
The SAGE scientists identified specific crops that help account for this growth.
In Brazil, for example, huge areas of rain forest have been replaced by soybeans, which aren't a traditional crop in South America. Production has been fueled by demand for soy from China.
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