Write a summary of the article Biofuels for Transportation and Industry.

Energy from biomass-materials derived from living or recently living organisms, such as plant materials or animal waste-is potentially the most challenging part of the Ecofys scenario. Bioenergy comes from a large variety of sources and is used in many different ways. Wood and charcoal have traditionally provided the main source of fuel for cooking and heating for hundreds of millions of people in the developing world. More recently, biofuels have begun to replace some petrol and diesel in vehicles.

In principle, biomass is a renewable resource-it is possible to grow new plants to replace the ones we use. Greenhouse gas emissions are lower than from fossil fuels, provided there is enough regrowth to absorb the carbon dioxide released, and good management practices are applied. Bioenergy also has potential to provide sustainable livelihoods for millions of people, particularly in Africa, Asia and Latin America. However, if produced unsustainably its environmental and social impacts can be devastating. We need comprehensive policies and mandatory certification to ensure bioenergy is produced to the highest standards.

Although the Ecofys scenario favours other renewable resources wherever possible, there are some applications where bioenergy is the only suitable replacement for fossil fuels. Aviation, shipping and long-haul trucking require liquid fuels with a high energy density; they cannot, with current technology and fuelling infrastructure, be electrified or powered by hydrogen. Some industrial processes, such as steel manufacturing, require fuels not only for their energy content, but as feedstocks with specific material properties. By 2050, 60 per cent of industrial fuels and heat will come from biomass. 13 percent of building heat will come from biomass and some biomass will still be needed in the electricity mix (about 13 per cent), for balancing purposes with other renewable energy technologies.

We can derive a significant proportion of the bioenergy needs in the Ecofys scenario from products that would otherwise go to waste. These include some plant residues from agriculture and food processing; sawdust and residues from forestry and wood processing; manure; and municipal waste. Using these resources up to a sustainable level has other environmental benefits, such as cutting methane and nitrogen emissions and water pollution from animal slurry, and reducing the need for landfill. In developing countries, more than 30 million households have their own biogas digesters for cooking and lighting. Some residues and waste products are already used, for example as soil conditioners; the Ecofys scenario accounts for these.

The second major source of biomass comes from forests. According to the Ecofys scenario, we will need more than 4.5 billion cubic metres of wood products for energy purposes by 2050 coming from harvesting and processing residues, wood waste and "complementary fellings"-the difference between the amount of wood we use and the maximum amount that we could sustainably harvest in forests that are already used commercially. This is preferable to taking wood from virgin forests and disturbing important habitats, although more intensive forestry is bound to affect biodiversity. In addition, some of the biomass traditionally used for heating and cooking in the developing world, which will largely be replaced by renewable energy sources such as solar energy, can also be used for more efficient bioenergy uses. All the same, meeting demand sustainably will be a huge challenge.

Bioenergy crops provide a possible source of liquid fuel-either vegetable oils from plants such as rapeseed, or in the form of ethanol derived from crops high in sugar, starch or cellulose. The Ecofys scenario suggests we will need around 250 million hectares of bioenergy crops-equal to about one-sixth of total global cropland-to meet projected demand. This has the potential to cause deforestation, food and water shortages, and other social and environmental impacts, so must be considered with utmost care.

With an expected 2 billion more mouths to feed by 2050, it is vital that increased biofuel cultivation does not use land and water that is needed to grow food for people or to sustain biodiversity. This is no easy challenge. While Ecofys has applied a series of safeguards in its analysis, land and water implications of bioenergy feedstock production will need further research, especially at the landscape level.

A possible long-term alternative source of high-density fuel included in this scenario is algae. Algae can be grown in vats of saltwater or wastewater on land not suitable for agriculture. Large-scale cultivation of algae for biofuel is currently in development. In the Ecofys scenario, algae begins to appear as a viable energy source around 2030, and only a fraction of its potential is included by 2050.

The apparent need for large amount of land for bioenergy is the aspect of the Ecofys scenario that produces the hardest challenges and raises the hardest questions.