Global food demand could double by 2050, according to a new projection by David Tilman, Regents Professor of Ecology in the University of Minnesota's College of Biological Sciences, and colleagues, including Jason Hill, assistant professor in the College of Food, Agricultural and Natural Resource Sciences. Producing that amount of food could significantly increase levels of carbon dioxide and nitrogen（氮） in the environment and cause the extinction of numerous species. But this can be avoided, the paper shows, if the high-yielding technologies of rich nations are adapted to work in poor nations, and if all nations use nitrogen fertilizers more efficiently.

"Agriculture's greenhouse gas emissions could double by 2050 if current trends in global food production continue," Tilman said. "Global agriculture already accounts for a third of all greenhouse gas emissions." Much of these emissions come from land clearing, which also threatens species with extinction.

The article shows that if poor nations continue current practices, they will clear a land area larger than the United States (two and a half billion acres) by 2050. But if richer nations help poorer nations improve yields to achievable levels, that could be reduced to half a billion acres.

The research, published Nov. 21 online by the Proceedings of the National Academy of Sciences, shows that adopting nitrogen-efficient "intensive" farming can meet future global food demand with much lower environmental impacts than the "extensive" farming practiced by many poor nations, which clear land to produce more food. The potential benefits are great. In 2005, crop yields for the wealthiest nations were more than 300 percent higher than yields for the poorest nations.

"Strategically intensifying crop production in developing and least-developed nations would reduce the overall environmental harm caused by food production, as well as provide a more equitable（公平的，公正的） food supply across the globe," said Hill.

The Food and Agriculture Organization (FAO) of the United Nations recently projected a 70 percent increase in demand. According to Tilman, either projection shows that the world faces major environmental problems unless agricultural practices change.

The environmental impacts of meeting demand depend on how global agriculture expands. Clearing land for agriculture and the use of fuel and fertilizers to grow crops increases carbon and nitrogen in the environment and causes species extinctions.

In the paper, Tilman and his collaborators explore different ways of meeting demand for food and their environmental effects. In essence, the options are to increase productivity on existing agricultural land, clear more land, or do a combination of both. They consider various scenarios in which the amount of nitrogen use, land cleared, and resulting greenhouse gas emissions differ.

"Our analyses show that we can save most of the Earth's remaining ecosystems by helping the poorer nations of the world feed themselves," Tilman said.

Christian Blazer, from the University of California Santa Barbara, collaborated with Tilman and Hill on the research. Belinda Befort, University of Minnesota College of Biological Sciences, also contributed.