This is an extract from a blog on the pages of the New York Times for June 6,2012 by Justin Gillis
“Humans have already converted about 43 percent of the ice-free land surface of the planet to uses like raising crops and livestock and building cities, the scientists said. Studies on a smaller scale have suggested that when more than 50 percent of a natural landscape is lost, the ecological web can collapse. The new paper essentially asks, what are the chances that will prove true for the planet as a whole?
In interviews, scientists involved in writing the paper acknowledged that the 50 percent threshold was simply a best guess, based on extrapolating the earlier research. But they said they were deeply concerned about many of the trends on the planet and the seeming inability of the world’s political leadership to grapple with them.”