Hartmut MICHEL

Nobel Laureate in Chemistry,
Max Planck Institute of Biophysics, Frankfurt am Main, Germany

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Title: Biofuels - can they help to reduce global warming or to solve the energy crisis?

It becomes generally accepted that the global warming which we undoubtedly observe, is the result of an increased concentration of greenhouse gases like carbon dioxide and methane in the atmosphere. Within this scenario it is evident that we have to reduce the emissions of carbon dioxide in order to stop or to decrease global warming. It will be necessary to switch from energy mainly based on fossil energy to renewable energy. One big hope is the use of biofuels like bioethanol, biodiesel, sundiesel, biogas and so on. Biofuels are products derived from photosynthesis of plants. It will be shown that the overall efficiency of photosynthesis is very low: less than one percent of the energy of the sunlight is stored in the form of biomass, and there is not much hope for a substantial improvement. Biogas and biodiesel per area unit and year contain about 0.4 % of the energy of the sunlight which the area unit has received in the same time. In addition at least 50 % of the energy which is contained in biogas or biodiesel had to be invested from conventional (fossil) energy sources to produce the biogas or biodiesel. Therefore, production and usage of biogas or biodiesel is not carbon dioxide neutral.

By comparison, usage of photovoltaic cells is more efficient by a factor of 50 to 100 with respect to energy conversion, and electric engines are fourfold as efficient as combustion engines. Consequently driving a car using electric batteries, loaded by photovoltaic cells, and electric engines requires only 0.2 % of the land that would be required using biofuels and combustion engines. Growing energy plants therefore is a very inefficient way of land use. The usage of biofuels made of palm oil or soy beans from tropical countries will enhance the deforestation, lead to a loss of the tropical rain forest and increase climatic changes. In addition we shall lose biodiversity and many biological compounds which might help fighting human diseases.