Greenhouse Gas Emissions from European Croplands

Agriculture is a significant source of the three main biogenic greenhouse gases (GHGs), carbon dioxide, nitrous oxide and methane. Within the EU-15, croplands are a significant source of both carbon dioxide (78 Mt C y-1) and nitrous oxide (~60 Mt
C-equivalents y-1). Since agricultural management is responsible for much of this flux, there is potential within the EU-15 to reduce this flux or to sequester soil carbon. Many factors drive GHG emissions from agriculture, a signifcant number of which are socio-political.

There are a number of methods available for accounting for GHGs but the most widely used are the IPCC 1996 revised guidelines. These provide default emission factors, but allow for country- / region -specific values for factors if available. Other, more sophisticated methods can also be used if available. Meta-analyses of data in Europe could help to provide better emission factors for use in Europe and in the future, dynamic emission factors (that respond to, for example, climate, soils, crop, fertiliser
etc.) might replace the static default emission factors currently used. Well-evaluated process-based models, linked to a series of benchmark sites, may play a role in GHG accounting in the future. Verification of GHG emission estimates will be difficult.

Greenhouse gas emissions in 1990 and 2000 for EU-15 are estimated to be as follows:
nitrous oxide-1990: 60 Mt C-equivalents y-1, nitrous oxide-2000: 57 Mt C-equivalents y-1, methane-1990: 54 Mt C-equivalents y-1, methane-2000: 50 Mt C-equivalents y-1, carbon dioxide-1990s: 78 Mt C y-1. By comparing country submissions to the United
Nations Framework Convention on Climate Change (UNFCCC) with estimates from IPCC defaults and other sources, discrepancies at the national level within the EU can be seen, though total EU-15 figures are similar across methods.

GHG mitigation options for croplands are examined. Per-area carbon sequestration rates are used to estimate mitigation potentials by comparing types and areas of landmanagement, in 1990 and 2000 and projected to 2010 for EU-15. For four country level case studies data are available: UK, Sweden, Belgium and Finland. In these countries, because cropland area is decreasing, and there are no current incentives in place to encourage soil carbon sequestration, we found that carbon sequestration has been small or negative in the EU-15 and all case study countries, except Belgium between 1990 and 2000. For all countries except Belgium, carbon sequestration is predicted to be negligible or negative to 2010, based on extrapolated trends. The only trend in agriculture that may be enhancing carbon stocks on croplands at present is organic farming, and that is highly uncertain. Previous studies have focused on the potential for carbon sequestration and have shown quite significant potential. This study, which examines the sequestration likely to occur by 2010, suggests that this potential will not be realised. Without incentives for carbon sequestration in the future, cropland carbon sequestration under Article 3.4 of the Kyoto Protocol will not
be an option in EU-15.

For reducing emissions of nitrous oxide (and methane) there are a number of options that offer significant GHG mitigation, most of which rely upon better fertiliser (mineral and organic) use and water management. The livestock and manure management
sectors offer greater mitigation potential for methane. There may be trade-offs between different greenhouse gases, especially between carbon dioxide and nitrous oxide, so it is important to assess potential mitigation options for their impact upon all greenhouse gases.

Future priorities include the need for a better understanding at the process level (especially in cropland soils), data / inventory collation and meta-analysis, further development of future scenarios of agricultural land-use and management, the development
of new technologies and methodologies for measuring soil carbon and greenhouse gas emissions simultaneously, process studies (both modelling and experimental) to couple the carbon and nitrogen cycles and a more complete biogeochemical / physical / socio-economic assessment of GHG mitigation options in agriculture.

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updated by Yvonne Hofmann,