Soil organic carbon (CLIM 027) - Assessment published Nov 2012
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Climate change (Primary topic)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 027
Key policy question: What is the trend in soil organic carbon in Europe?
- Soil carbon stocks in the EU-27 are around 75 billion tonnes of carbon; around 50 % of which is located in Ireland, Finland, Sweden and the United Kingdom (because of the large area of peatlands in these countries).
- The largest emissions of CO2 from soils are due to conversion (drainage) of organic soils, and amount to 20–40 tonnes of CO2 per hectare per year. The most effective option to manage soil carbon in order to mitigate climate change is to preserve existing stocks in soils, and especially the large stocks in peat and other soils with a high content of organic carbon.
- On average, soils in Europe are most likely to be accumulating carbon. Soils under grassland and forests are a carbon sink (estimated up to 80 million tonnes of carbon per year) whereas soils under arable land are a smaller carbon source (estimated from 10–40 million tonnes of carbon per year).
- The effects of climate change on soil organic carbon and soil respiration are complex, and depend on distinct climatic and biotic drivers. However, they lack rigorous supporting datasets.
- Climate change is expected to have an impact on soil carbon in the long term, but changes in the short term will more likely be driven by land management practices and land use change
Variations in topsoil organic carbon content across Europe
Note: The map shows the percentage of organic carbon content in the surface horizon of soils in Europe. The darker regions correspond to soils with high values of organic carbon. The darkest colours, especially in Estonia, Fennoscandinavia, Ireland and the United Kingdom, denote peatlands.
- European Soil Database 2003 provided by Joint Research Centre (JRC)
- Corine Land Cover 2006 raster data provided by European Environment Agency (EEA)
Around 45 % of the mineral soils in Europe have low or very low organic carbon content (0–2 %) and 45 % have a medium content (2–6 %) [i]. Figure 1 shows that low levels are particularly evident in southern Europe where 74 % of the land is covered by soils that have less than 2 % of organic carbon in the topsoil (0–30 cm) [ii]. However, areas of low organic carbon can be found almost everywhere, including in some parts of more northern countries such as Belgium, France, Germany, Norway and the United Kingdom. More than 50 % of EU soil organic carbon stocks are to be found in peatlands [iii].
In general, most soils across Europe are likely to be accumulating carbon. Except under drainage conditions, grassland soils accumulate carbon, although there is a high uncertainty as to the rate. Croplands generally act as a carbon source, although existing estimates are varied. Forest soils generally accumulate carbon (estimates range from 17 to 39 million tonnes per year [iv]).
However, estimates of European CO2, CH4 and N2O fluxes between 2000 and 2005, using both top-down estimates based on atmospheric observations and bottom-up estimates derived from ground-based measurements, suggest that CH4 emissions from livestock and N2O emissions from arable agriculture are fully compensated by the CO2 sink provided by forests and grasslands [v].
Soil organic carbon levels are determined mainly by the balance between net primary production (NPP) from vegetation and the rate of decomposition of the organic material. While climate change is expected to have an impact on soil carbon in the long term, changes in the short term will more likely be driven by land management practices and land-use change, which can mask the evidence of climate change impact on soil carbon stocks. The effects of climate change on soil are complex and lack rigorous supporting datasets.
[i] G. Louwagie, S. H. Gay, and A. Burrell, Final report on the project ‘Sustainable Agriculture and Soil Conservation (SoCo)’ JRC Scientific and Technical Reports (Luxembourg: European Commission, Joint Research Centre, 2009).
[ii] P. Zdruli, R.J.A. Jones, and L. Montanarella, Organic Matter in the Soils of Southern Europe European Soil Bureau Technical Report. (Luxembourg: Publications Office of the European Union, 2004).
[iii] R. Schils et al., Final report on review of existing information on the interrelations between soil and climate change (Climsoil). Final Report for the European Commission’s Directorate-General for the Environment (Brussels: European Commission, 2008).
[iv] Schils et al., Final report on review of existing information on the interrelations between soil and climate change (Climsoil). Final Report for the European Commission’s Directorate-General for the Environment.
[v] E.D. Schulze et al., „Importance of methane and nitrous oxide for Europe’s terrestrial greenhouse-gas balance“, Nature Geoscience 2 (2009): 842–850, doi:10.1038/ngeo686.
European Soil Database 2003
provided by Joint Research Centre (JRC)
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