Forest biomass is used in many countries as an abundant and easily accessible source of
renewable energy. While forest biomass has certain advantages in terms of carbon sink
capability, it cannot be considered an emission-free energy source, and the environmental
differences among various forest biomass sources have been unclear. This study uses life cycle
assessment for two purposes. The first is to quantify the environmental impacts of the energy
production of a small-scale, combined heat and power production plant utilizing different forest
biomasses. The second aim is to estimate the change in environmental impacts on district heat
production from natural gas when partially replacing it by heat from the combined heat and
power plant. The environmental impacts include global warming potential, acidification
potential, and eutrophication potential. The calculated environmental impacts of utilizing
different forest biofuels in the CHP plant in relation to produced energy are 2.2–5.1
gCO2,eq./MJenergy excluding biogenic carbon emission, 59–66 gCO2,eq./MJenergy with biogenic carbon
emission, and 133–175 mgSO2,eq./MJenergy and 18–22 mgPO34-,eq./MJenergy with pellets, showing the
highest values. The results indicate that by using forest biomass instead of natural gas in energy
production, the global climate impacts are reduced when biogenic carbon is excluded, while the
local effects are higher (acidification potential and eutrophication potential). Including biogenic
carbon reduces the calculated climate benefit since the total emissions end up being 4–7 % over
those of natural gas use. The potential benefits need to be weighed against the possible
drawbacks.