Greenhouse impact of fossil, forest residues and jatropha diesel: A static and dynamic assessment

Biofuels have been recognised as one option for mitigating climate change. However, in order to show the sustainability of biomass-based fuels, an assessment of the savings in Greenhouse Gas (GHG) emissions compared to fossil fuels needs to be clearly shown. There are two ways to measure the greenhouse impact of an activity. It can be done statically or dynamically, by using Global Warming Potential (GWP) or Radiative Forcing (RF) respectively. This article compares these two methods for assessing the greenhouse impact and introduces two more rarely discussed and lesser-known raw materials for biodiesel production, forest residues in Finland and jatropha in India, as well as their greenhouse impact compared to fossil fuel from a life cycle perspective. The analyses made with GWP and RF show some differences. Using a time horizon of 100 and 300 years, the magnitude of the greenhouse impact of jatropha biodiesel assessed with GWP and RF differs by only a few percent. When the greenhouse impact of forest residue-based Fischer-Tropsch (FT) diesel was assessed, the difference between the GWP and RF assessment was larger, up to 10%. This is also a reflection of the more accurate calculation possibility of the greenhouse impact with RF in which the exponential and time dependent decay of forest residues can be taken into account. Compared to fossil diesel, the greenhouse impact of jatropha and forest residue-based biodiesel was approximately one-third less, irrespective of the assessment method. This, however, may not be enough to fulfil the requirements of the European Union (EU) on the sustainability of biofuels.