When considering this, it is important to mention that there is no template greenhouse gas balance (GHG balance sheet) available. Depending on the harvesting and land use scenario, different GHG emissions occur. The calculation of greenhouse gas emissions in relation to land-use changes is very complex and is therefore illustrated in different scenarios. In the partnership with Hamburg, a variety of values and scenarios are discussed, and the best strategy is developed. In abstract terms, it is about the optimal management of the carbon sink "bush landscape" for the benefit of the people and ecosystems in Namibia.
In principle, the energetic use of biomass releases as much CO2 as was previously fixed by the growth of the plant. However, emissions from harvesting, processing and transport must be added.
Reducing or amplifying effects of GHG emissions are effected by changing land use.
A CO2 emission of 72 kgCO2/t or 14 kgCO2/MWh are to be expected for mechanical harvesting and processing into wood pellets with large machines.
The following values are set for transport:
Expected Scenario
This results in CO2 emissions of around 86 kg CO2/t biomass on average over the entire transport from the biomass park in Namibia to Hamburg. Based on the calorific value of wood pellets from Namibia (here 5 MWh/t), a transport-related CO2 load of 18 kgCO2/MWh results. By way of comparison, according to the Ökoinstitut e.V. 20061, emissions of heating oil for extraction and transport from OECD or Russia range from 15 to 28 kgCO2/MWh. The CO2 emissions caused in Namibia might even be lower due to lower down times and good capacity utilisation (biomass industrial parks).
For the overall balance shown below, these figures were converted to emissions per hectare and year. A once-off harvest of 9.6 t of wood pellets in 20 years was assumed. This calculation results 0.28 tCO2/ha for harvesting, 0.44 tCO2/ha for processing and 1.03 tCO2/ha for transport.
It can be assumed that after the bush thinning, the numbers of livestock in the pasture will increase. Since ruminants emit methane, possible additional greenhouse gas emissions of 3.5 tCO2/ha were calculated and also added.
The greenhouse gases of the multifunctional land use discussed in this partnership and described in the section "Potentials of bush wood" reflect values that fluctuate between sink growth (new binding of CO2) and slight release.
It has been observed that in the system of multifunctional land use (stripe system) bush thinning leads to a direct growth of grass on the same area. It also seems reasonable to give room for renewed but controlled bush growth after the thinning of the shoots, despite the first or more years of harvesting the saplings after thinning. It is assumed that after about 5-6 years, the renatured grass savannah will once again provide space for bush growth. This model is FSC certified, see "National Forest Stewardship Standard of Namibia“2).
In the sustainable system of multifunctional land use, however, care is taken to ensure that bushes regrow on a restored area only if another area has been bush thinned.
Over a cycle of 20 years, the carbon released by the energetic use of the bush biomass is partially re-captured again by the regeneration of the bushes (approximately 0.52 tCO2/ha/a; or 10.4 tCO2/ha/20a).
In addition, the regrowing grass biomass binds carbon dioxide of around 0.52 tCO2/ha/a (10.2 tCO2/ha/20a).
The soil beneath the grass is usually richer in humus than the barren soil below a bush covered surface (cp. Li et al 2016)3. this has a positive effect on soil organic carbon (SOC). For this purpose, 0.33 tCO2/ha/a (6.6 tCO2/ha/20a) will be credited (cp. Seebauer et al 2019).
The total binding capacity is therefore 27.2 t CO2 per hectare over 20 years.
The following graphic shows this (GHG) scenario based on a "Life Cycle Analyses" (LCA) approach. The figures are based on the results of existing studies and concrete calculations, with the ongoing scientific discourse on values drawing an upcoming positive picture.
In summary emissions in the described model are minus 1.27 tCO2/ha or minus 0.026 tCO2/MWh. In direct comparison with natural gas, which has a CO2 footprint of around 0.250 tCO2/MWh, the use of bush wood would reduce greenhouse gas emissions by 111%.
If the project is implemented, regular monitoring and evaluation of the greenhouse gas balance will of course be provided for.
References:
Liebich, A.: Höhe der Treibhausgasemissionen (entlang der gesamten Prozesskette) von importiertem flüssigen Erdgas im Vergleich mit anderen Energieträgern. IFEU, Präsentation, 24.10.2019
Seebauer, M., Pinkwart, A., Schwarz, B., Hartz, C.:POLICY BRIEF. Greenhouse Gas Assessment of Bush Control and Biomass Utilization in Namibia, UNIQUE. Date unknown
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1 http://iinas.org/tl_files/iinas/downloads/GEMIS/2006_vorketten_iwo.pdf
2 https://africa.fsc.org/
3 Li, He, Haihua Shen, Leiyi Chen, Taoyu Liu, Huifeng Hu, Xia Zhao, Luhong Zhou, Pujin Zhang & Jingyun Fang, 2016, Effects of shrub encroachment on soil organic carbon in global grasslands, Metastudy in www.nature.com/scientific reports/ , Scientific Reports | 6:28974 | DOI: 10.1038/srep28974