Beneficial biofuels

A policy forum in this week's Science outlines the types of biofuel that could actually lead to net reductions in greenhouse gas emissions and have other societal or environmental benefits. The paper argues that current methods of growing energy-intensive biofuel crops (like corn in the US) on existing agricultural land and/or clearing land for biofuel crops (like palm oil in SE Asia) are clearly unacceptable, but that not all biofuels are inherently evil.

Here's their list of the potentially beneficial biofuels, for those without a subscription to Science:

Perennial plants grown on degraded lands abandoned for agricultural use

The two keys here are: i) using land that has not been storing large amounts of carbon, so clearing the land will not release that carbon, and ii) using land is not at all part of an existing or planned future production system so that biofuel production does not have a cascading effect on food production

Crop residues

This includes residues beyond what should be left on the field to regenerate the soil.

Sustainably harvested wood and forest residues

There is a lot of leftover from forest clearing and from pulp and paper production.

Double crops and mixed cropping systems

Fall or winter biofuel crops could be grown after the harvest of the traditional summer crops ("double" crops). This would eliminate the need to clear land and release carbon in order to grow biofuel crops. Winter or off-season cover crops are good for the soil anyway. And [the paper asserts that] biofuels grown as double crops could avoid the problem of competing for land with food production. This argument is debatable; one could also argue that we could increase double cropping to decrease land needs for food production.

Municipal and industrial wastes

Solid waste could be turned into liquid fuels. This would actually be a good solution in island nations where disposal is difficult.