Scientists in Germany have demonstrated the viability of biofuels as a sustainable fuel source that does not compete with agriculture. In their scenario, which they assert is realistic, affordable and CO2-neutral, trees grown on degraded land throughout the world are used as a primary source of fuel, converted to a usable form using other renewable energies. Their report is published in the journal Naturwissenschaften. According to the International Energy Agency (IEA), roughly 87% of the global energy mix comes from depleting fuel sources such as oil and coal, and most of this supply (with the exception of nuclear energy) is carbon-rich. Energy reserves are expected to run out in the course of the next 75 years at the current rate of consumption, and most likely earlier considering the ever-increasing demand. Finding ways to meet the growing global energy demand while reducing carbon emissions is the focus of intense research, but the option of using biofuels as a sustainable energy source has largely been dismissed. The prospect of a 'biomass scenario' has been considered unrealistic because cultivating plants for fuel on arable land competes with the growing needs of agriculture as the world's population increases. In the new biofuels scenario, Professor Jürgen O. Metzger of the University of Oldenburg and Professor Aloys Huettermann of the University of Goettingen propose cultivating fast-growing trees planted in a mosaic pattern (rather than in huge plantations) on degraded lands (rather than on arable land) as a primary fuel source, using other renewable energy sources to convert the biomass to a usable form. This scenario is indeed realistic, the authors conclude. Furthermore, it has the potential to address the serious problems of continuing land degradation and deforestation, which contribute significantly to erosion and the pollution of coastal waters. 'Mankind has been degrading, in historical times, some billion hectares of areas originally forested and covered with vegetation,' the authors write. They show how planting trees with very low nutrient and water requirements could eventually restore the fertility of the soil, the importance of which, they say, cannot be underestimated. 'A high percentage of these degraded areas should be available and suited for afforestation,' the authors reason. 'To combat ongoing desertification and to improve the fertility of soils, it would be in the objective interest of the respective countries, of the local population, and in the general interest of mankind to afforest these degraded areas and to use the biomass continuously for the production of the necessary energy, fuel, materials, and chemicals of the respective country and, if possible, for export.' The scientists demonstrate the cost-effectiveness of their scenario and the amount of land required. They show that investments are not higher than in coal power stations and are much lower than in nuclear power plants, and estimate that up to 3.6 gigahectares of land could be made available for bioenergy production by 2050. An additional benefit, they explain, is that biomass for energy use can be cultivated in all countries and each country should be able to produce an important fraction of its primary energy supply. This keeps transportation costs low. Using biomass as an energy source, the authors assert, is carbon neutral: the CO2 created by its use is not more than the amount it needs to grow. It therefore has the potential to help slow down the build-up of CO2 in the atmosphere. Biomass is also a convenient way to store energy, halt runoff pollution in water supplies and, to some extent, control desertification. However, many challenges remain. Of central importance is the development of new technologies to convert the chemical energy stored in the biomass to electrical energy more efficiently. The same could be said for fossil fuels, they add. Growing trees for fuel is only one aspect of meeting the world's growing energy needs, according to the study, and several sustainable energy sources need to be thrown in to the mix. Also, 'energy conservation and a more efficient usage of primary energy have to be a most important part of the solution,' the study concludes. One of the major strengths of the biofuels scenario is the relatively short time it would take to see an impact. 'Afforestation can be started immediately, has an impact of [a] few years, and may be realised in some decades,' the study concludes. 'If afforestation [had] been started in 1992 [...] we could observe already today an impact which would steadily increase and [this] biomass would contribute an important percentage to the primary energy supply in 2030.'