The simplified life cycle of biofuels starts by the source material (e.g. biomass) absorbing CO2 from the atmosphere, and emitting the absorbed carbon when being burnt as fuel, which is then available for biofuel crops for absorption. According to this simplified life cycle, biofuels should have a net zero effect on CO2 levels. However, the picture is more complex and not all biofuels are the same:
- Some biodiesel is produced from cattle fat (tallow). The carbon footprint from cattle farming emissions is significant. Although the argument can be made that cattle is mainly farmed for meat production, there is a considerable amount that is allocated to the by-products for biofuels based on their relative market value.
- Fertilisers and pesticides required for production of biofuels add to the impacts of the latter. Biofuels from crops such as canola oil and corn therefore have comparable life cycle carbon emissions compared with conventional fuels.
When considering the full life cycle of biofuels, the lowest environmental impacts are from waste products where the initial use is not dedicated to biofuel production. An example of this is used cooking oil being diverted from waste to use as a fuel source.
It can then be concluded that biofuels from waste products are better fuel choices, while those from crops grown specifically for fuel purposes can have much higher environmental impacts.
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