[Editor’s Note: There’s a nasty dig at organic agriculture in this article that makes no sense, and there is no thought given to the fact that regional and local sustainable agriculture could help with some of the issues the article addresses, but there are still a lot of interesting facts here.]

By 2050, the world will host nine billion people-and that’s if population growth slows in much of the developing world. Today, at least one billion people are chronically malnourished or starving. Simply to maintain that sad state of affairs would require the clearing (read: deforestation) of 900 million additional hectares of land, according to Pedro Sanchez, director of the Tropical Agriculture and Rural Environment Program at The Earth Institute at Columbia University.

The bad news beyond the impacts on people, plants and animals of that kind of deforestation: There isn’t that much land available. At most, we might be able to add 100 million hectares to the 4.3 billion already under cultivation worldwide.

“Agriculture is the main driver of most ecological problems on the planet,” said economist Jeffrey Sachs, Scientific American columnist and Earth Institute director. “We are literally eating away the other species on the planet.”

Sachs made his remarks yesterday at a symposium hosted by the institute on how to improve agriculture to address the mounting challenge of feeding the world while combating climate change and stopping the wholesale loss of biodiversity, among other interrelated issues.

Agriculture-thanks to deforestation, nitrous oxide from fields, methane from cattle and rice paddies-is responsible for one third of global greenhouse gas emissions from human activity, making emissions from transporting food, known as “food miles,” a “rounding error,” said ecologist Jonathan Foley, director of the Institute on the Environment (IonE) at the University of Minnesota. Pasture has become the dominant ecosystem on the planet, he added, and humans directly employ some 40 percent of the surface of the planet. “Very little of that is urban.”

In addition, agriculture accounts for at least 85 percent of human water consumption-a growing concern as aquifers diminish and hydrology changes in the face of climate change. And, by Sanchez’s rough calculation, humans now use some 171 million tons of nitrogen as fertilizer every year, much of which ends up polluting lakes, rivers, streams and even the ocean. “Fifty-four percent of that is fertilizer-the Haber-Bosch process; 11 percent is atmospheric deposition-the plus side of pollution; 18 percent is in situ fixation,” or nitrogen-fixing cover crops, like legumes, Sanchez said.