page_title: Environmental impact of biodiesel
section_title: Greenhouse gas emissions
hierarchical_section_title: Environmental impact of biodiesel / Greenhouse gas emissions
caption_attribution_description: Excel Graph showing the Carbon Intensity of US Soy Biodiesel. Derived from information found in the UK crown copyright document.[1]
context_page_description: The environmental impact of biodiesel is diverse.
context_section_description: An often mentioned incentive for using biodiesel is its capacity to lower greenhouse gas emissions compared to those of fossil fuels. Whether this is true or not depends on many factors. A general critic to biodiesel is the land use change, which have potential to cause even more emissions than what would be caused by using fossil fuels alone. Yet this problem would be fixed with algal biofuel which can use land unsuitable for agriculture.
  Carbon dioxide is one of the major greenhouse gases. Although the burning of biodiesel produces carbon dioxide emissions similar to those from ordinary fossil fuels, the plant feedstock used in the production absorbs carbon dioxide from the atmosphere when it grows. Plants absorb carbon dioxide through a process known as photosynthesis which allows it to store energy from sunlight in the form of sugars and starches. After the biomass is converted into biodiesel and burned as fuel the energy and carbon is released again. Some of that energy can be used to power an engine while the carbon dioxide is released back into the atmosphere.
  When considering the total amount of greenhouse gas emissions it is therefore important to consider the whole production process and what indirect effects such production might cause. The effect on carbon dioxide emissions is highly dependent on production methods and the type of feedstock used. Calculating the carbon intensity of biofuels is a complex and inexact process, and is highly dependent on the assumptions made in the calculation. A calculation usually includes:
  Emissions from growing the feedstock (e.g. Petrochemicals used in fertilizers)
  Emissions from transporting the feedstock to the factory
  Emissions from processing the feedstock into biodiesel
  Absorption of CO2 Emissions from growing the feedstock
  Other factors can be very significant but are sometimes not considered. These include:
  Emissions from the change in land use of the area where the fuel feedstock is grown.
  Emissions from transportation of the biodiesel from the factory to its point of use
  The efficiency of the biodiesel compared with standard diesel
  The amount of Carbon Dioxide produced at the tail pipe. (Biodiesel can produce 4.7% more)
  The benefits due to the production of useful by-products, such as cattle feed or glycerine
  If land use change is not considered and assuming today's production methods, biodiesel from rapeseed and sunflower oil produce 45%-65% lower greenhouse gas emissions than petrodiesel. However, there is ongoing research to improve the efficiency of the production process. Biodiesel produced from used cooking oil or other waste fat could reduce CO₂ emissions by as much as 85%. As long as the feedstock is grown on existing cropland, land use change has little or no effect on greenhouse gas emissions. However, there is concern that increased feedstock production directly affects the rate of deforestation. Such clearcutting cause carbon stored in the forest, soil and peat layers to be released. The amount of greenhouse gas emissions from deforestation is so large that the benefits from lower emissions (caused by biodiesel use alone) would be negligible for hundreds of years. Biofuel produced from feedstock such as palm oil could therefore cause much higher carbon dioxide emissions than some types of fossil fuels.
caption: Calculation of Carbon Intensity of Soy biodiesel grown in the US and burnt in the UK, using figures calculated by the UK government for the purposes of the Renewable transport fuel obligation.[1]
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