Biofuels are often regarded as carbon neutral due to the balance between the carbon they emit when burned and the carbon absorbed by the feedstock during its growth.

Biofuels are produced from biomass, which refers to organic material sourced from living or recently living organisms, predominantly plants. These plants play a crucial role in the carbon cycle by absorbing carbon dioxide ($\text{CO}_2$) from the atmosphere through the process of photosynthesis. During photosynthesis, plants convert sunlight into energy, incorporating the absorbed carbon into their structures. When these plants are harvested and transformed into biofuels, the carbon stored within them is released back into the atmosphere upon combustion. This cyclical process of carbon absorption and release is the basis for considering biofuels as carbon neutral.

However, it is essential to recognize that this does not imply biofuels have no environmental impact. The cultivation, harvesting, and conversion of plants into biofuels can require significant energy inputs, often sourced from fossil fuels, which may lead to net carbon emissions. For instance, if a forest is cleared to cultivate biofuel crops, the carbon stored in the forest is released, and it can take years for the newly planted crops to sequester an equivalent amount of carbon.

Additionally, the use of fertilizers and pesticides in the cultivation of biofuel crops can contribute to the release of other greenhouse gases, such as nitrous oxide ($\text{N}_2\text{O}$), which is a far more potent greenhouse gas than carbon dioxide ($\text{CO}_2$).

Consequently, while the theoretical basis for the carbon neutrality of biofuels is sound, the actual carbon neutrality of a specific biofuel can vary significantly. Factors influencing this include the type of feedstock used, the agricultural practices employed, and the energy inputs required for processing and transportation.

In summary, biofuels are deemed carbon neutral because they absorb as much carbon during their growth as they emit upon combustion. Nonetheless, the overall environmental impact of biofuels is influenced by a variety of factors.