Technical and policy aspects of strategies to decrease greenhouse gas emissions from agriculture

Agricultural activities greatly contribute to the global net flux of CH4, N2O and CO2 from the terrestrial biosphere into the atmosphere. For CH4 and N2O, the net contribution is in the order of 40ÐBecause of this relatively large contribution, there is an urgent need for the implementation of effective strategies to decrease the net flux of CH4, N2O and CO2 from agriculture. The objectives of this paper are to review the various measures that have been proposed so far and to discuss the constraints and challenges. A large number of suggestions for decreasing emissions of CH4, N2O and CO2 from agriculture can be found in literature. Common to most of these abatement measures is that the suggested potentials to decrease the emissions of CO2, CH4 and N2O from agriculture are large. Common to most of the measures is also the 'single gas' and 'source-oriented' approach. In most papers it has been implicitly assumed that farmers are able and willing to implement the proposed measures. So far, none of the measures has been consciously implemented and tested at farm scale. The major challenge of policy makers is to formulate effective and efficient policies and measures, using the potentials of the abatement measures proposed so far, and in an international setting with still highly uncertain cause-effect relationships. Major constraints for policy makers follow from the complexities and possible feed back and side effects of abatement measures, from the many stakeholders involved, often with contrasting views, and from the unfamiliarity of farmers with the problem of climate change. Because of the many complexities and interactions involved, policy makers should follow two tracks. Priority should be given to chain-oriented measures, i.e. measures that aim at an increased carbon, nitrogen and water use efficiencies in the whole food chain, above source-oriented measures, i.e. measures that aim at decreased emission from specific sources. Chain-oriented measures should fit in with other environmentalpolicies that aim at increasing resource use efficiency, to be effective and efficient.