Greenhouse impacts of the use of peat and wood for energy

Atmospheric concentrations of greenhouse gases may well double or increase even more during the next hundred years. The resultant disturbance in the global radiation energy balance (radiative forcing) may change almost as much. Stabilizing these concentrations at a level innocuous to the climate - the aim expressed in the Climate Convention - will take decades, perhaps more than a hundred years, to carry out. Radiative forcing caused by Finnish emissions is currently of the order of 3 mW/m2. Global radiative forcing caused by greenhouse gas emissions resulting from human activity is approximately 2.5 W/m2. This study examines the greenhouse impacts of using peat and wood for energy and the time factors involved, taking the entire energy production chain and renewal of the energy source into account. The greenhouse effects of peat and wood use are compared with those of fossil fuels. The calculations apply to test cases. Financial considerations and other sources of energy are not dealt with. Greenhouse effects are measured in terms of radiative forcing caused by using an energy resource. The calculations are made per units of primary energy. The study further proposes ways to apply the results obtained to assessing the extent to which radiative forcing caused by Finland could be reduced by the use of peat or wood fuels. The aim is to indicate the basic factors related to combating climate change in each case examined. Results depend heavily on the assumptions on which the calculations for each scenario are based. The calculations take into account emissions of CO2, CH4, N2O and possible sinks of CO2 arising from energy production. The emissions and sinks of each chain of energy production are calculated as a function of time, deducting emissions which would arise in the reference case, in which energy production is not begun. Real emissions due to production are obtained by deducting emissions in the reference case from emissions which arise during production. The difference is used as a basis for calculating radiative forcing per unit of energy produced. Changes in concentrations of atmospheric greenhouse gases and radiative forcing caused by them take place quite slowly owing to the slow removal of these gases from the atmosphere. Renewal of the bioenergy resources examined is also a slow process. Thus, the greenhouse impacts of energy production chains must be examined over a relatively extended period of time. On the basis of the results, the energy production chains examined can be roughly divided into three categories on the basis of radiative forcing caused by them within one hundred years. The smallest increase per amount of energy produced is caused by the use of wood waste, forest residues, wood from first thinning and, in the long run, wood from regeneration felling and possibly wood from coppices cultivated for energy use. The next group, which affects radiative forcing slightly more, consists of natural coppices, peat from cultivated peatlands, natural gas and oil. Coal and peat from virgin or forest-drained peatlands increase radiative forcing most. The longer the period over which impacts are examined, the greater the advantages of renewable fuels compared with fossil fuels; short-term differences are smaller. Radiative forcing arising from energy production can be reduced quite substantially by replacing energy production chains (e.g. coal) which cause high radiative forcing with chains which give rise to minimum radiative forcing per unit of energy. Of the measures examined here, an effective way of reducing Finland's radiative forcing would be to start by exploiting, to the extent possible, forest residues from harvesting and wood from first thinning instead of coal. These fuels could probably replace more than half of the energy generated with coal in Finland, causing very low radiative forcing. If we wish to replace all coal-generated energy, the next best alternatives are wood from regeneration felling, natural coppices, peat from cultivated peatland and natural gas. All in all, this would result in a reduction of approximately 1 mW/m2, one third of Finland's current radiative forcing, over a period of one hundred years.