why are biofuels bad? @steveghan1 challenged me to a better critique than "they're dumb". so here goes:

first, why they're good: b/c the CO2 released from burning biomass was absorbed from the atmosphere during the growth of the plant, there is no net increase in atmospheic CO2

why they're bad: the rate of photosynthesis limits the power generated by biomass to ~0.6 W/m^2 of farmed land. this is much less than the 20-40 W/m^2 you get from solar power. this means that growing reasonable amounts of biomass will require enormous amounts of land.

the land requirement is problematic. we know from experience that much of the additional land will come from clearing forest. This deforestation releases carbon dioxide into the atmosphere, and it causes a host of other local environmental impacts, such as ecosystem degradation.

also, the farming methods used to grow the biomass have to be carefully considered. production of fertilizer, for example, requires large inputs of energy.

If the fertilizer used in the growth of the biomass comes from fossil fuels, it might take as much fossil fuel energy to grow the biomass as is saved by burning the biomass to produce energy.

finally, it is becoming clear that using food, such as corn, as feedstock for biomass energy stresses the food supply. In particular, the increased competition for food (or land) raises food prices, an impact disproportionately felt by the poor.