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Biofuels are not emission-free: a new method for impact assessment



In her thesis work at VTT Technical Research Centre of Finland, climate change expert Johanna Kirkinen has studied the impacts on climate change of various biomass-based and peat-based fuels used in Finland. The impact of forest residues proved to be the least important. In her thesis, Kirkinen presents a new and exceptional approach to life cycle calculations of fuels for assessing their greenhouse impacts.

Combating climate change requires a significant reduction in greenhouse gas emissions. Biomass-based fuels are considered to be a means of achieving these emission reductions. However, biofuels are not carbon-neutral or emission-free, as is often believed. They cause an effect that heats the atmosphere when the entire life cycle of the fuel’s production and use is taken into consideration. The greenhouse gas impacts and possible emission reductions of the fuels must, therefore, be proven clearly and comprehensively.

In her thesis work, Kirkinen studied the greenhouse impacts of the following fuel chains: forest residues, reed canary grass, coal, natural gas, and peat. Diesel fuels studied included the forest residues and peat-based Fischer-Tropsch diesel, Jatropha diesel, and fossil diesel. During the work on her thesis Kirkinen developed the Relative Radiative Forcing Commitment (RRFC) assessment method, which illustrates the significance of the greenhouse impacts. It shows the heating effect of greenhouse gases as a concrete ratio compared to the energy generated by the fuel chain.

Forest residues has the smallest climate impact

Over a hundred-year time span, forest residues cause the least climate impact, but they still heat the atmosphere by 20–40 times compared to the amount of energy it produces. The atmospheric heating is caused by radiative forcing, which is a result of the increased greenhouse gas concentrations, caused by greenhouse gas emissions. Reed canary grass has a slightly greater impact than forest residues (climate impact between 20 and 50). Natural gas heats the atmosphere 100–110 times and coal 170–190 times the amount of energy they produce. The use of peat has a slightly larger or smaller greenhouse impact than coal, depending on the type of peat bog it was collected from.

According to Kirkinen’s thesis, there is considerable justification in forest energy remaining clearly the most important source of renewable energy in Finland, in line with the scenarios presented in the government’s foresight report.

The role of climate impact assessment will increase

The climate impact of fuels must always be comprehensively examined, taking into consideration the entire life cycle of the fuel chain, and emissions at different stages. In her thesis, Kirkinen presents a new and exceptional approach for assessing the greenhouse impacts of fuel life cycles,taking into consideration the reduction of thermal radiation from Earth to space. The assessment method is dynamic, allowing the calculation of the greenhouse impact for each year studied. The climate impact was assessed using radiative forcing, which is especially well suited to the assessment of the greenhouse impact of biomass-based fuels, when emissions and/or sinks are considered over a time period of several decades. This is often the case, for example, with land use and resulting emissions.

If one wishes to limit global warming to 2–3 degrees, the consideration of time spans in the assessment of greenhouse impacts is emphasised, as emissions must be drastically reduced as early as during the next couple of decades. The timing of the greenhouse effect will thus be a very important factor when considering the sustainability of biofuels.

The role of assessing and reporting the greenhouse impacts of products and services will increase when moving towards a low-carbon society. Clear and definite information is required, not only for the support of effective climate change reduction strategies, but also for increasing awareness. Emissions should not be assessed merely at the end of an exhaust pipe or a smokestack, but taking into consideration the overall climate impact of production and use.


Photograph for media use: Johanna Kirkinen