Writing team: Patrick Avato (Germany/Italy), Rodney J. Brown (USA), Moses Kairo (Kenya)

Bioenergy has recently received considerable public atten­tion. Rising costs of fossil fuels, concerns about energy security, increased awareness of climate change, domestic agricultural interests and potentially positive effects for eco­nomic development all contribute to its appeal for policy makers and private investors. Bioenergy as defined in the IAASTD covers all forms of energy derived from biomass, e.g., plants and plant-derived materials. Bioenergy is cat­egorized as traditional or modern, depending on the history of use and technological complexity. Traditional bioenergy includes low technology uses including direct combustion of firewood, charcoal or animal manure for heat generation. Modern bioenergy is comprised of electricity, light and heat produced from solid, liquid or gasified biomass and liquid biofuels for transport. Liquid biofuels for transport can be categorized as first generation, produced from starch, sugar or oil containing agricultural crops, or next generation. Next generation (also referred to as second, third or fourth generation) biofuels are produced from a variety of biomass materials, e.g., specially grown energy crops, agricultural and forestry residues and other cellulosic material [CWANA Chapter 2; Global Chapters 3, 6; NAE Chapter 4].
As biomass feedstocks are widely available, bioenergy offers an attractive complement to fossil fuels and thus has potential to alleviate concerns of a geopolitical and en­ergy security nature. However, only a small part of glob­ally available biomass can be exploited in an economically, environmentally and socially sustainable way. Currently, about 2.3% of global primary energy is supplied by modern sources of bioenergy such as ethanol, biodiesel, or electricity and industrial process heat [Global Chapter 3].
The economics of bioenergy, and particularly the posi­tive or negative social and environmental externalities, vary strongly, depending on the source of biomass, type of con­version technology and on local circumstances and insti­tutions. Many questions in development of bioenergy will require further research. Agricultural knowledge, science, and technology (AKST) can play a critical role in improving benefits and reducing potential risks and costs but comple­mentary efforts are needed in the areas of policies, capacity building, and investment to facilitate a socially, economi­cally, and environmentally sustainable food, feed, fiber, and fuels economy. Specific options and challenges associated with the different categories are discussed in the following

section. Aspects that are crosscutting are discussed in a sepa­rate section.

Traditional Bioenergy
Millions of people in developing countries depend on tra­ditional biofuels for their most basic cooking and heating needs (e.g., wood fuels in traditional cook stoves or char­coal). Dependence on traditional bioenergy is highly cor­related with low income levels and is most prevalent in sub-Saharan Africa and South Asia due to a lack of afford­able alternatives. In some countries, the share of biomass in energy consumption can reach up to 90%. Within countries, the use of biomass is heavily skewed toward the lowest in­come groups and rural areas [CWANA Chapter 2; Global Chapter 3; SSA Chapter 2].
     Reliance on traditional bioenergy can stifle development by posing considerable environmental, health, economic and social challenges. Traditional biomass is usually asso­ciated with time consuming and unsustainable harvesting, hazardous pollution and low end-use efficiency, and in the case of manure and agricultural residues depletion of soil by removal of organic matter and nutrients. Collecting fuel is time-consuming, reducing the time that can be devoted to productive uses including farming and education. Air pol­lution from biomass combustion leads to asthma and other respiratory problems which lead to 1.5 million premature deaths per year7 [Global Chapter 3; SSA Chapter 2]. Efforts in the past at making available improved and more efficient traditional  bioenergy technologies   (e.g.,  improved cook stoves) have led to mixed results. New and improved ef­forts and approaches are therefore needed that build on and expand these efforts. Moreover, other options must be ex­plored to expand the availability and use of modern energy solutions. Such technologies differ widely from each other in terms of economic, social and environmental implications and may include fossil fuels, extensions of electricity grids, and forms of distributed energy including modern forms of bioenergy (see section on bioelectricity and bioheat).

First Generation Biofuels
First generation biofuels consist today predominantly of bioethanol and biodiesel, even though other fuels such as methanol, propanol and butanol may play a larger role in the future. Produced from agricultural crops such as maize

⁸ This number includes deaths caused by the combustion of coal in the homestead.