A map of the world's tropical forests has revealed that millions of hectares of trees were cut back to make way for crops in recent years.
Created from high-resolution satellite images, the map shows the extent of deforestation in the tropics with unprecedented accuracy.
Between 2000 and 2005, at least 27.2m hectares (68m acres) of tropical forests were cleared to make way for farming. Almost half of the deforested land was in Brazil, nearly four times more than the next most deforested country, Indonesia, which accounted for 12.8% of cleared land.
Scientists led by Matthew Hansen at South Dakota State University created the map to help inform conservationists and politicians about the state of the world's forests. While figures on deforestation are already compiled by the UN Food and Agriculture Organisation, they are based on unverified estimates submitted by individual countries, and rarely describe where in a country forests are being cleared.
Recent estimates by the UN suggest that around 13m hectares of the world's forests are lost to deforestation each year, with South America alone losing more than 4m hectares a year.
"We wanted to be able to pinpoint exactly where deforestation was happening, because that gives you much more information for policy makers to act upon," said Fred Stolle at Conservation International in Washington DC.
The scientists collected images taken between 2000 and 2005 by Nasa's Modis satellite network, which photographs the surface of the Earth every one to two days in 500m-wide snapshots.
The researchers used the images to identify deforestation "hotspots" in the tropics, and then created a detailed map using a second satellite network called Landsat, which is accurate to within 30m.
According to the map, over the five-year period, Brazil lost 3.6% of its forest cover, Indonesia 3.4%, Latin America 1.2%, the rest of Asia 2.7% and Africa 0.8%. The study appears in the US journal, Proceedings of the National Academy of Sciences.
The map showed that deforestation in Indonesia was largely concentrated in just two regions, and that much of it was peatland. "The peatlands are essentially all carbon, so if you clear it and fire it, an enormous amount of carbon will be emitted into the atmosphere," said Stolle. "Without a precise map, we would not know that level of detail."
The researchers hope to produce annual updates of the map to show trends in deforestation.
The map is a conservative estimate of deforestation because it only shows where forests have been cut down and not replaced. It does not take into account selective logging, areas where forests have been replanted, or general degradation of forests.