Revised figures for the carbon footprint of growing wheat and oilseed rape for biofuel
Scientists at Aarhus University have updated the figures for the impact on the climate of growing wheat and oilseed rape for biofuels.
Ethanol and biodiesel produced from agricultural crops are considered as sustainable biofuels with an increasing potential to replace fossil fuels. An important driver for this development is the desire to limit the total climate impact from the transport sector.
However, the production of biofuels, based for example on growing winter wheat and winter oilseed rape, requires an input of labour and additives that have to be included in the total figure for the climate impact of biofuels.
Against this backdrop, the EU introduced the Renewable Energy Directive that sets a maximum value for the carbon footprint of the value chain if biofuels are to be included in the EU target of 10 percent renewable energy in the transport sector by 2020.
According to current regulations, the carbon footprint of biofuels must be 35 percent lower than that of fossil fuels. This value will be increased to 50 percent in 2017. In the calculation of the total climate impact of the biofuel production chain, the greenhouse gas emission during crop cultivation is an independent and important factor.
In 2009 the Danish Energy Agency asked the Ministry of Food, Agriculture and Fisheries to prepare a report on greenhouse gas emissions from the growing of crops for biofuel in Denmark. Using a Swedish report as a starting point, the work was delegated to DCA – Danish Centre for Food and Agriculture, who with the input from scientists at the Department of Agroecology, Aarhus University, met this part of Denmark's obligations within the Renewable Energy Directive of the European Commission.
In 2014 The Danish AgriFish Agency asked DCA to examine whether there were grounds for a revision of the Danish calculations. The scientists behind the report collected any new results that had emerged since 2010 and an updated 2015 report has now been accepted by the European Commission. The report can be downloaded here.
The new report shows that estimates of greenhouse gas emissions from winter wheat for the five Danish regions in 2015 ranged from 18.9 to 23.4 g CO2 equivalents per megajoule of ethanol; in 2010, the corresponding figures were from 20.1 to 24.4 g CO2 equivalents. For winter oilseed rape the range for 2015 was from 21.4 to 24.4 g CO2 equivalents per megajoule biodiesel, where in 2010 they were from 23.7 to 28.2 CO2 equivalents. This means that the Danish figures almost always are below the standard values listed in the Renewable Energy Directive of, respectively, 23 and 29 g CO2 equivalents for wheat and oilseed rape.
Background to the new estimates
Associate Professor at the Department of Agroecology, Lars Elsgaard, carried out the final calculations and he points out that in addition to using an updated methodology for calculating emissions from leached nitrogen, the report has been revised to reflect the new figures for crop yield from Statistics Denmark and the latest certified data for the carbon footprint of producing mineral N fertilizers. The environmental impact of the production of the power needed in the process has also fallen by more than 35 percent from 2010 to 2015, as documented by Energinet.dk.
The European Commission has additionally requested a special analysis of greenhouse gas emissions from organic soils. Here Aarhus University's new chart of the carbon content of organic soils has enabled a more detailed response from the Danish side. But according to Associate Professor Lars Elsgaard this does not mean that the latest calculations are definitive:
- This type of calculation is based on a large number of estimates and assumptions. As we stated already in the 2010 report, it is natural that these assumptions are assessed on a regular basis to reflect new knowledge and technological development. What is happening is that the preconditions for using crops for energy purposes are constantly evolving. What we are required to do is to document the numbers that we use in the calculations for the EU, says Lars Elsgaard, who also points to the need for better standardized calculations if inter-country comparisons of GHG emissions should make sense
Associate professor Lars Elsgaard
Department of Agroecology – Soil Fertility
Telephone: +45 87157674