The aim of using wood as a source of energy is to reduce carbon dioxide emissions from energy production and to increase the proportion of renewable sources. The quantity of wood biomass harvested from Finnish forests for energy production has increased to five million cubic metres in the 2000s, and according to the Government's bioenergy policy, will be increased further to 13.5 million cubic metres by 2020.
Wood can replace fossil fuels and reduce emissions from them, but the harvesting of wood biomass from forests simultaneously weakens their carbon sink capacity.
Carbon sink changes are insufficiently accounted for in many calculations used in climate policy, which can easily lead to the climate benefits achieved through forest energy being overstated.
The weaker carbon sink capacity of forests diminishes emission reductions
According to the study, the increase in forest energy production will lower the annual carbon sink capacity of Finnish forests by 6.2 million tonnes of CO2 by 2020. Tree biomass will remain as carbon sink but the soil will transform from carbon sink to carbon source and its carbon reserves will begin to dwindle.
The forest energy produced can replace an estimated 10.7 million tonnes of carbon dioxide emissions from coal, 8.7 million tonnes from heating oil or 7.6 million tonnes from natural gas. Taking into account both emissions and changes to the carbon sink, Finland's net emissions to the atmosphere will decrease by 1.4 - 4.5 million carbon dioxide tonnes, depending on the fossil fuel replaced. Hence the difference between fossil fuel emission reductions achieved through forest energy, and actual net reductions in emissions, is significant.
- Forest energy is not as low in emissions as is generally assumed. Harvesting of wood from forests reduces the quantity of atmospheric carbon accumulated in forests, even though growing forests do take up carbon from the atmosphere. Logging residue, such as branches, wood from first thinnings and tree stumps, would store coal for a long time if left to rot in the forest. The climate benefit achieved by carbon storage is similar to that of, for instance, long lasting products made of wood, explains Leading Researcher Jari Liski of the Finnish Environment Institute.
Forest energy emissions reduce with time
Emissions due to the reduction of carbon reserves in forests are highest when the use of forest energy commences or the quantity used increases. As a result, a changeover to forest energy is not a particularly quick way to reduce emissions from Finland's energy production. If the aim is to reduce emissions quickly to a level sufficient to tackle climate change (for instance to the warming by two degrees as outlined at the Cancun climate conference) energy production emissions must be reduced in other, faster ways in addition to a shift to forest energy.
If tree biomass, such as branches and wood from first thinnings, that forms the most short-lived carbon storage in forests and rots the fastest, is used for energy production, forest energy emissions would remain significantly lower as production continues. Emissions from tree stumps used as sources of energy would remain high for decades, however, because if left in the forest, they would have decayed slowly and stored carbon for a long time. If the energy use of tree stumps is increased in line with the Government's bioenergy policy, by 2020 it will result in emissions as high as those from producing the same amount of energy using oil in Finland. Then, emissions from the energy use of branches will be up to 50 per cent lower.
Hence, emissions from forest energy can be substantially reduced by targeting production at those parts of trees with more advantageous climate impacts, such as branches and wood from first thinnings. If, however, high production targets for bioenergy are set, the use of less advantageous tree stumps may be necessary in order to achieve them. This will undermine the overall impact of forest energy on climate change.
Climate policy calculation formulae overestimate the climate benefits of forest energy
Many calculation formulae for emissions, used in climate policy, do not take sufficient account of the impact of forest energy on the carbon sink of forests, while reductions in fossil fuel emissions achievable through the use of renewable wood are accounted for in full. For instance, Finland's emissions calculated on the basis of the Kyoto Protocol do not include any adjustment for changes in the carbon sink of forests caused by the use of wood as an energy source. The European Union's calculation formulae for biofuels only take account of changes in carbon sinks where the production of biomass transforms forest into another form of land use. By contrast with these calculation formulae, the annual greenhouse gas inventory conducted under the UN Climate Convention, which is not applicable to obligatory emission restrictions, takes full account of forest energy impacts on the carbon sink of forests. This inventory can be compared to other calculation formulae.
Because changes in the capacity of forests to act as carbon sinks is not adequately accounted for, many climate policy calculation formulae overestimate actual emission reductions and climate benefits achievable through forest energy. As a result, the emission figures used in climate policy for forest energy are not always comparable with the emission levels used in climate research.