In her thesis work at VTT Technical Research Centre of Finland, Johanna Kirkinen has studied the impacts on climate change of various biomass-based fuels used in Finland. The impact of forest residues proved to be the least important.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, according to Johanna Kirkinen.In her thesis work, Kirkinen studied the greenhouse impacts of the following fuel chains: forest residues, reed canary grass, coal, natural gas, and peat. Forest residues has the smallest climate impact, but they still heat the atmosphere by 20–40 times compared to the amount of energy they produce. 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.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, according to Johanna Kirkinen.