Whether biofuel helps the climate depends on where its crops are grown
Burning biofuel releases carbon that the crops pulled out of the air only months before, which is why it is often called carbon-neutral. Yet if forests or grasslands are cleared to grow those crops, the total emissions can match fossil fuels. In other cases, biofuel use actually removes more carbon than it emits.
Biofuel is made from biomass in a short time, rather than over the ages it takes to form oil. It can come from plants or from farm, household or industrial waste, and is used mostly for transport, though also for heat and electricity. The IPCC defines biomass here as organic material that has not fossilised, so coal does not count. Definitions differ: some include solid fuels such as wood, while others reserve the word for liquid or gas fuels for vehicles.
Two kinds dominate. Bioethanol is alcohol fermented from sugary or starchy harvests like corn, cane and sweet sorghum, with trees and grasses under development as non-food sources; it can run engines neat as E100 but is usually blended into petrol to raise octane and cut emissions. Biodiesel is made from oils or fats by a process called transesterification and is likewise usually mixed into diesel, lowering soot, carbon monoxide and hydrocarbons. The United States leads in bioethanol, the EU in biodiesel, and Brazil runs many vehicles on bioethanol, including flex-fuel cars sold only there. Annual output carries about 2.2 exajoules of energy in bioethanol and 1.8 in biodiesel.
First-generation biofuels come from food crops on arable land, which fuels the food-versus-fuel argument. Advanced, or second- and third-generation, biofuels avoid that clash by using waste and energy crops, including rice straw, rice husks, wood chips and sawdust. Critics also point to deforestation and lost biodiversity tied to production, and life-cycle studies give widely varying answers depending on feedstock, method and assumptions.
Demand is forecast to rise by 56 percent between 2022 and 2027, when biofuels should supply 5.4 percent of transport fuel, including 1 percent of aviation fuel. The International Energy Agency argues they are best saved for uses that are hard to electrify, such as ships and planes, and some policies have been faulted for favouring road vehicles instead.
Source: Biofuel
