Climate Impact from Peat Utilisation in Sweden

The climate impact from the use of peat for energy production in Sweden has been evaluated in terms of contribution to atmospheric radiative forcing. This was done by attempting to answer the question 'What will be the climate impact if one would use 1 m2 of mire for peat extraction during 20 years?'. Two different methods of after-treatment were studied: afforestation and restoration of wetland. The climate impact from a peatland - wetland scenario and a peatland - forestation - bioenergy scenario was compared to the climate impact from coal, natural gas and forest residues. Sensitivity analyses were performed to evaluate which parameters that are important to take into consideration in order to minimize the climate impact from peat utilisation. In a 'multiple generation scenario' we investigate the climate impact if 1 Mega Joule (MJ) of energy is produced every year for 300 years from peat compared to other energy sources. The main conclusions from the study are: • The accumulated radiative forcing from the peatland - forestation - bioenergy scenario over a long time perspective (300 years) is estimated to be 1.35 mJ/m2/m2 extraction area assuming a medium-high forest growth rate and medium original methane emissions from the virgin mire. This is below the corresponding values for coal 3.13 mJ/m2/m2 extraction area and natural gas, 1.71 mJ/m2/m2 extraction area, but higher than the value for forest residues, 0.42 mJ/m2/ m2 extraction area. A 'best-best-case' scenario, i.e. with high forest growth rate combined with high 'avoided' methane (CH4) emissions, will generate accumulated radiative forcing comparable to using forest residues for energy production. A 'worst-worst-case' scenario, with low growth rate and low 'avoided' CH4 emissions, will generate radiative forcing somewhere in between natural gas and coal. • The accumulated radiative forcing from the peatland - wetland scenario over a 300-year perspective is estimated to be 0.73-1.80 mJ/m2/m2 extraction area depending on the assumed carbon (C) uptake rates for the wetland and assuming a medium-high methane emissions from a restored wetland. The corresponding values for coal is 1.88 mJ/m2/m2 extraction area, for natural gas 1.06 mJ/m2/m2 extraction area and for forest residues 0.10 mJ/m2/m2 extraction area. A 'best-best-case' scenario (i.e. with high carbon dioxide (CO 2)-uptake combined with high 'avoided' CH4 emissions and low methane emissions from the restored wetland) will generate accumulated radiative forcing that decreases and reaches zero after 240 years. A 'worst-worst-case' (i.e. with low CO2-uptake combined with low 'avoided' methane emissions and high CH4 emissions from the restored wetland) will generate radiative forcing higher than coal over the entire time period. • The accumulated radiative forcing in the 'multiple generations' - scenarios over a 300-year perspective producing 1 MJ/year is estimated to be 0.089 mJ/m2 for the scenario 'Peat forestation - bioenergy', 0.097 mJ/m2 for the scenario 'Peat wetland with high CO2- uptake' and 0.140 mJ/m2 for the scenario 'Peat wetland with low CO2-uptake'. Corresponding values for coal is 0.160 mJ/m 2, for natural gas 0.083 mJ/m2 and for forest residues 0.015 mJ/m2. Using a longer time perspective than 300 years will result in lower accumulated radiative forcing from the scenario 'Peat wetland with high CO2-uptake'. This is due to the negative instantaneous forcing that occurs after 200 years for each added generation. • It is important to consider CH4 emissions from the virgin mire when choosing mires for utilization. Low original methane emissions give significantly higher total climate impact than high original emissions do. • Afforestation on areas previously used for peat extraction should be performed in a way that gives a high forest growth rate, both for the extraction area and the surrounding area. A high forest growth rate gives lower climate impact than a low forest growth rate. • There are great uncertainties related to the data used for emissions and uptake of greenhouse gases in restored wetlands. The mechanisms affecting these emissions and uptake should be studied further.