Agence France-Presse: The use of crop-based biofuels could speed up rather than slow down global warming by fueling the destruction of rainforests, scientists warned Saturday. Once heralded as the answer to oil, biofuels have become increasingly controversial because of their impact on food prices and the amount of energy it takes to produce them. They could also be responsible for pumping far more carbon dioxide into the atmosphere than they could possibly save as a replacement for fossil fuels, …