Soil organic carbon (CLIM 027) - Assessment published Sep 2008
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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: ..
- Soil in the EU contains around 71 gigatonnes of organic carbon, nearly 10 % of the carbon accumulated in the atmosphere. An increase in temperature and a reduction in moisture tend to accelerate the decomposition of organic material, leading to a decline in soil organic carbon stocks in Europe and an increase in CO2 emissions to the atmosphere. This could wipe out all the savings that other sectors of the economy are achieving to reduce anthropogenic greenhouse gas emissions.
- Losses of soil organic carbon have already been observed in measurements in various European regions over the past 25 years.
- The projected changes in the climate during the 21st century will change the contribution of soil to the CO2 cycle in most areas of the EU. Adapted land-use and management practices could be implemented to counterbalance the climate-induced decline of carbon levels in soil.
Changes in soil organic carbon content across England and Wales between 1978 and 2003
Note: The map shows the difference in soil organic carbon content
Bellamy, P. H.; Loveland, P. J.; Bradley, R. I.; Lark, R. M. and Kirk, G. J. D., 2005. Carbon losses from all soils across England and Wales 1978-2003. Nature 437: 245248.
Projected changes in soil organic carbon for cropland 1990-2080
Note: Predicted changes in soil organic carbon for croplands 1990–2080. The image on the left shows changes due to climate change only while the map on the right shows changes as a result of variations in net primary production and the advent of new technologies related to crop management (e.g. machinery, pesticides, herbicides, agronomic knowledge of farmers) and breeding (development of higher yielding varieties through improved stress resistance and/or yield potential) that result in yield increases.
Smith, P.; Smith, J.; Wattenbach, M.; Meyer, J.; Lindner, M.; Zaehle, S.; Hiederer, R.; Jones, R. J. A.; Montanarella, L.; Rounsevell, M.; Reginster, I. and Kankaanpää, S., 2006. Projected changes in mineral soil carbon of European forests, 1990-2100. Canadian Journal of Soil Science 86: 159169.
In the past, losses in organic carbon in the soil were driven mainly by conversion of land for the production of agricultural crops. A survey of Belgian croplands (210 000 soil samples taken between 1989 and 1999) indicates a mean annual loss in organic carbon of 76 gCm-2 (Sleutel et al., 2003). A large-scale inventory in Austria estimated that croplands were losing 24 gCm-2 annually (Dersch and Boehm, 1997). The general intensification of farming in the past is likely to have exceeded the effect of changes in the climate on soil organic carbon on agricultural land. Peat lands in Europe have been a significant sink for atmospheric CO2 since the last glacial maximum. Currently they are estimated to hold about 42 Gt carbon, about 60 % of all carbon stocked in European soils, and are therefore a considerable component of the European carbon budget (Byrne et al., 2004). The annual loss of carbon due to drainage of peat lands is in the range of 0 to 47 gCm-2 (Lappalainen, 1996).
The amount of organic carbon in the soil is determined mainly by the balance between net primary production (NPP) from vegetation and the rate of decomposition of the organic material. Without an increase in NPP, soil carbon for cropland may decrease by 9 to 12 t C ha-1. When taking account of changes in NPP and technological advances, the amount of organic carbon on cropland could increase by 1-7 t C ha-1 (Smith, et al., 2005). Figure 2 shows that climate change may cause loss (red) of soil organic carbon for most areas in Europe. This decline could be reversed (blue) if adaptation measures in the agricultural sector to enhance soil carbon were implemented. It should be noted that these modelled projected changes are very uncertain.
National Soils Inventory (NSI)
provided by Cranfield University (National Soil Resources Institute)
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