Biofuel

Biofuel is a fuel produced over a short time span from biomass, rather than through the slow natural processes that form fossil fuels. It can be made from plants or from agricultural, domestic, or industrial bio-waste, and is mostly used for transportation, though it can also be used for heating and electricity. Biofuels are regarded as a renewable energy source, but their use has been subject to criticism regarding the 'food vs fuel' debate, varied assessments of sustainability, and ongoing deforestation and biodiversity loss.

Environmental impacts

When burned in an engine, biofuels generally emit fewer greenhouse gases than fossil fuels and are often considered carbon-neutral, because the carbon released was originally captured from the atmosphere by the crops used in production. However, life-cycle assessments reveal that large emissions can arise from land-use changes required to grow additional biofuel feedstocks. The climate impact of biofuels varies widely depending on the feedstock, production method, data used, and methodological choices; in some scenarios, emissions are comparable to fossil fuels, while in others, the use of biofuel can result in negative emissions.

Extent of production and use

Global demand for biofuels is predicted to increase significantly, with production expected to supply a notable share of transport fuels, including a small fraction of aviation fuel. The International Energy Agency recommends using biofuels primarily for applications that are difficult to electrify, such as shipping and aviation. The two most common types are bioethanol and biodiesel. The United States is the largest producer of bioethanol, the European Union is the largest producer of biodiesel, and Brazil produces and uses large amounts of bioethanol in vehicles, including in some flex-fuel cars exclusive to that country.

Bioethanol is an alcohol made by fermenting carbohydrates from crops like maize, sugarcane, or sweet sorghum, and is often used as a gasoline additive. Biodiesel is produced from oils or fats through transesterification and is commonly used as a diesel additive. First-generation biofuels are made from food crops grown on arable land, while advanced biofuels, also called second- or third-generation, use non-food feedstocks such as agricultural residues, waste oils, and energy crops grown on marginal land to avoid competing with food production.