The biggest probem with many of the alternatives that use biomas as the source of energy is that the more acreage needed to produce the biomas, the less undisturbed land (rainforest, etc) we will have. Consequently, many species may become endangered or even extinct. This deforestation may actually be worse than the carbon dioxide currently produced by using petroleum and coal. We are already seeing this in Brazil where the rainforests are being eaten up in order to produce more soybeans and other crops because of the amount of crops in the US being used to create biofuels.