The world has come full circle. A century ago our first transportation biofuels — the hay and oats fed to our horses — were replaced by gasoline. Today, ethanol from corn and biodiesel from soybeans have begun edging out gasoline and diesel.

This has been hailed as an overwhelmingly positive development that will help us reduce the threat of climate change and ease our dependence on foreign oil. In political circles, ethanol is the flavor of the day, and presidential candidates have been cycling through Iowa extolling its benefits. Lost in the ethanol-induced euphoria, however, is the fact that three of our most fundamental needs — food, energy, and a livable and sustainable environment — are now in direct conflict. Moreover, our recent analyses of the full costs and benefits of various biofuels, performed at the University of Minnesota, present a markedly different and more nuanced picture than has been heard on the campaign trail.

Some biofuels, if properly produced, do have the potential to provide climate-friendly energy, but where and how can we grow them? Our most fertile lands are already dedicated to food production. As demand for both food and energy increases, competition for fertile lands could raise food prices enough to drive the poorer third of the globe into malnourishment. The destruction of rainforests and other ecosystems to make new farmland would threaten the continued existence of countless animal and plant species and would increase the amount of climate-changing carbon dioxide in the atmosphere.

Finding and implementing solutions to the food, fuel and environment conflict is one of the greatest challenges facing humanity. But solutions will be neither adopted nor sought until we understand the interlinked problems we face.

Fossil fuel use has pushed atmospheric carbon dioxide higher than at any time during the past half-million years. The global population has increased threefold in the past century and will increase by half again, to 9 billion people, by 2050. Global food and fossil energy consumption are on trajectories to double by 2050.

Biofuels, such as ethanol made from corn, have the potential to provide us with cleaner energy. But because of how corn ethanol currently is made, only about 20 percent of each gallon is "new" energy. That is because it takes a lot of "old" fossil energy to make it: diesel to run tractors, natural gas to make fertilizer and, of course, fuel to run the refineries that convert corn to ethanol.