Biofuels have lately been indicated as a promising source of cheap and sustainable energy. In this paper we argue that some important ethical and environmental issues have also to be addressed: (1) the conflict between biofuels production and global food security, particularly in developing countries, and (2) the limits of the Human Appropriation of ecosystem services and Net Primary Productivity. We warn that large scale conversion of crops, grasslands, natural and semi-natural ecosystem, (such as the conversion of grasslands to cellulosic (...) ethanol production, or plantation of sugar cane and palm oil), may have detrimental social and ecological consequences. Social effects may concern: (1) food security, especially in developing countries, leading to an increase of the price of staple food, (2) transnational corporations and big landowners establishing larger and larger landholdings in conflict with indigenous areas and the subsistence of small farmers. Ecological effects may concern: (1) competition with grazing wild and domesticated animals (e.g., millions of grazing livestock in USA prairies), (2) an excessive appropriation of Net Primary Production from ecosystems, (3) threatening biodiversity preservation and soil fertility. We claim that is it well known how ecological and social issues are strictly interwoven and that large scale biofuels production, by putting high pressure on both fronts, may trigger dangerous feedbacks, also considering the critical fact that 9 billion people are expected to inhabit the planet by 2050. There is a need to conduct serious and deep analysis on the environmental and social impact of large scale biofuels production before important energy policies are launched at global level. Biofuels will not represent an energetic panacea and their role in the overall energy consumption will remain marginal in our present highly energivorous society, while their effect on food security and environment preservation may have detrimental results. We should also have the courage to face two key issues: (1) we cannot keep increasing resources consumption at present pace, and have to change our life style accordingly, and (2) we have to deal with population growth; we cannot expect to have 9–10 billions people inhabiting the earth by 2050, without this representing a major impact on its support system. (shrink)