If biofuels can be made without using huge amounts of energy then they would be carbon neutral. This means that when they are burned the amount of carbon dioxide released into the atmosphere is similar to the amount absorbed by the growing plant when it carries out photosynthesis. At present a large amount of energy, provided by fossil fuels, is required to grow the biofuel crops, transport them and process them into ethanol. When fossil fuels are burned they release huge amounts of stored carbon that have been trapped for thousands of years: releasing the stored carbon upsets the carbon cycle. At present biofuels are not carbon neutral.