While the general consensus is clear that corn ethanol isn't as great as once proclaimed, biodiesel has somewhat escaped the criticism swarm (palm plantation biodiesel being the big exception). That may change now that a new study from the Woods Institute for the Environment has found that crop-based biofuels, any of them, will likely speed up global warming rates. The study found that, overall, biofuels pump "far more carbon dioxide into the atmosphere than they could possibly save as a replacement for fossil fuels," according to the AFP. The study authors looked at 20 years' worth (1980-2000) of satellite photos of tropical areas and discovered that half of the biofuel cropland came from virgin rainforests. The imbalance of this deforestation means that it'll take somewhere between 40 and 120 years to pay back the "carbon debt." Algae and cellulosic biofuel sources can not get here soon enough.