If you are growing crops to be used as biofuels, then, by definition, you are not using that land for any other purpose.

That simple but profound insight is central to an important new study published by the World Resources Institute (WRI).

The study from this well-known environmental group should make policymakers worldwide think twice about instituting or expanding ambitious biofuel programs.

Researchers Tim Searchinger and Ralph Heimlich make the case that policies that lead to setting aside land for biofuels production – like our own ethanol policies in the United States – ultimately do little to curb greenhouse gas emissions.

Moreover, such policies take away land that could – and should – be used for other purposes, such as growing food.

According to the U.N.’s Food and Agricultural Organization, the calories from crops which will be needed to feed the earth’s population are expected to grow 70 percent between 2006 and 2050. Yet, Searchinger and Heimlich note, “three-quarters of the world’s land area capable of supporting vegetation is already managed or harvested to meet human food and fiber needs.”

Meeting this demand growth will be difficult to achieve if policies continue to incentivize the use of crops for biofuels and the harvesting of trees for power generation.

A further problem is that the harvesting of standing forests reduces carbon storage opportunities, resulting in more greenhouse gas emissions. (It can also have ramifications for endangered species, but that was beyond the scope of the study.)

Underlying these difficulties is the fundamental fact of physics that creating energy from biomass is woefully inefficient. The authors write:

Although photosynthesis is an effective means of producing food, wood products, and carbon stored in vegetation, it is an inefficient means of converting the energy in the sun’s rays into a form of non-food energy useable by people. …

[Biofuels’] low conversion efficiencies explain why it takes a large amount of productive land to yield a small amount of bioenergy, and why bioenergy can so greatly increase the global competition for land.

As an aside, I’ll point out that one of the features that make fossil fuels indispensable to today’s world is that they are sources of highly concentrated energy.

Those searching for alternatives to oil and natural gas often have trouble acknowledging the relative physical limitations of other sources, particularly biofuels like ethanol. But such limitations can’t simply be wished away.

Even assuming large increases in efficiency, Searchinger and Heimlich write, “the quest for bioenergy at a meaningful scale is both unrealistic and unsustainable.”

They recommend, among other things, that governments rethink biofuels policies, especially the subsidies and mandates for biofuels from crops that rely on the dedicated use of land.

They also call for a more honest accounting of GHG emissions savings tied to biofuels policies. In their eyes, biofuels advocates make a “double counting” error that inflates their supposed emissions reductions benefits. This error has been used to justify biofuels policies around the world.

The World Resources Institute should be commended for a valuable contribution to the public policy debate. There’s a lot more to the study than what I have recounted here, so download it and read for yourself.

Its findings offer more grist for the mill, so to speak, of the ongoing discussion over U.S. biofuels policies and the future of the Renewable Fuels Standard.

Let’s hope this report gets a wide hearing and sows the seeds for change around the world.