2 Approach to the evidence review
2.1 Selection of mitigation options
There is a wide variety of potential GHG MOs within the ALULUCF sector. For example, the 2015 GHG marginal abatement cost curves for agriculture (Eory et al. 2015) identified 26 potential measures for Scottish farming. For the current report to add most value it was agreed that the evidence review would focus on a selection of MOs. Following discussion with the Scottish Government and after taking into consideration the 2015 GHG marginal abatement cost curves for agriculture, independent expert advice received by the Scottish Government and a recent Department for Energy and Climate Change commissioned report (Smith et al, 2017) into wider impacts of climate change MOs, the following twelve MOs were selected.
Table 2 Mitigation options assessed
|Mitigation Option||Brief Description|
|MO1||Developing on-farm renewable energy sources||Land managed on Scottish farms often has excellent renewable energy potential, and renewables are an important part of Scotland's effort to reduce GHG emissions.|
|MO2||Increased uptake of precision farming techniques
||Precision farming includes management practices and a range of technologies enabling farmers to analyse information on soil, crop and animal quality. This can contribute to reducing energy use by machinery, and/or the GHG emission intensity of crop and livestock products.|
|MO3||Achieving and maintaining optimal soil pH level (grassland and arable land)||The Scottish Government are in the planning stages of introducing compulsory soil testing on improved agricultural land. This should give farmers the tools to understand and manage their soil and could help reduce over-application of fertiliser while simultaneously increasing farm profitability.|
|MO4||Anaerobic digesters for manure processing (community AD facilities of around 750 KW - 1 MW)||AD of manure can reduce methane ( CH 4) emissions from storage and can provide alternative energy sources, thus providing further, indirect, GHG savings.|
||Agroforestry can sequester carbon and also enable farms to provide a range of ecosystem services while having little or no negative effect on food production.|
|MO6||Incorporating more legumes in grass mixes/crop rotations
||Legumes have symbiotic relationships with bacteria allowing them to fix atmospheric nitrogen and use this in place of nitrogen provided by synthetic fertilisers. They are also supply nitrogen to crops they are mixed with (e.g. clover-grass mixtures) and to subsequent crop rotations (e.g. peas in one year and cereals in the next).|
|MO7||Optimising use of mineral nitrogen fertiliser||Optimising the use of mineral fertiliser means that the fertiliser will be used more efficiently, thus reducing application rates.|
|MO8||Low-emission storage and application of manure||This approach can reduce NH 3 (providing savings in indirect N 2O emissions) and CH 4 emissions, and can result in retaining more nutrients for target crops.|
|MO9||Improving livestock health
||Livestock diseases can lead to impacts on livestock performance. Treating and preventing diseases tend to increase productivity and lead to decreases in the emissions intensity of the meat, milk or eggs.|
|MO10||Reduced livestock product consumption
||Positive health impact of a dietary shift from meat-consumption could be the single largest co-benefit of any GHG-mitigating measure examined. Evidence indicates combined GHG and health benefits warrants further investigation of WIs.|
|MO11||Afforestation||Afforestation is potentially a major contributor to reducing the net GHG emissions by sequestering carbon in the soil and as woody biomass.|
|MO12||Peatland restoration||Peatland restoration can reduce the carbon dioxide ( CO 2) emissions associated with the degradation of soil carbon content in peatlands that have been (partially) drained.|
As agreed with the Scottish Government a different approach has been taken in reviewing the wider impacts associated with the waste sector. For this sector attention has focused on potential employment benefits from diverting tonnages from landfill to recycling, with a high level consideration of non-territorial emissions.
2.2 Wider impacts and the impact pathway
The wider impacts associated with GHG mitigation in the ALULUCF and waste sectors are many and varied. Likewise, the pathway through which these co-benefits and adverse side-effects arise can be complex. For example, a MO can have a wide range of direct effects, such as impacting on NH 3 levels or the level of nitrogen leaching. These primary effects can then translate into intermediate impacts i.e. changes in air quality and water quality respectively, which in turn can lead to impacts on human well-being (endpoint impacts), such as changes in human health.
An understanding of the different pathways through which MOs can have wider impacts is important in the development of policies. Once the pathways are identified policies can be designed to maximize the co-benefits and mitigate the adverse side-effects.
This evidence review has found that the majority of qualitative evidence focuses on the direct effects, but ultimately the monetary values of impacts are directly related with endpoint impacts. However, the relation between direct impacts and end-point impacts is not of a one-to-one identity: direct impacts contribute to multiple intermediate impacts that in turn contribute to multiple end-point impacts. Conversely, changes in various aspects of human well-being (e.g. human health or cultural well-being) depend on multiple primary impacts. Disentangling these complexities and quantitatively attributing the end-point or intermediate impacts to direct impacts is often unfeasible, but certain parts of these pathways are becoming well- described.
As direct evidence on the wider impacts or agricultural production practices is mostly available at the direct impact level, the main focus of the report was placed on these impacts. For some of these impacts some level of monetary valuation is already available. The direct impacts considered were NH 3, NO x, PM, nitrogen and phosphorous as the main agriculture-related drivers of air and water quality, ultimately impacting on agricultural production, human health and biodiversity; water use; animal health and crop health, which have downstream impact on food production; animal welfare (contributing to spiritual well-being); land cover and land use, which has wide-ranging impacts on agricultural production, biodiversity, flood regulation, human health and spiritual wellbeing; and the economic and social primary impact of income, consumer and producer surplus and employment.
Four intermediate impacts were also included in the assessment: soil quality, flood regulation, biodiversity and resource efficiency. Considering soil quality, flood regulation and biodiversity instead of the direct impacts driving them (e.g. soil carbon content, soil moisture, land cover, air and water quality) is more suitable due to the available monetary values and valuation methodologies. The biodiversity impacts are considered only at the local scale, i.e. direct impacts in local biodiversity, rather than off-site impacts mediated through changes in air quality or water quality. Resource efficiency is a highly aggregated wider impact including material use, like nitrogen, phosphorous, water, and energy use. This was added as a wider impact to help the alignment of the findings with the Scottish Government's circular economy aspirations.
Finally, three endpoint impacts were also included. Human health was explicitly considered as the food consumption demand side MO has a strong impact on it, which cannot be captured looking at impacts upstream in the pathway. The scarcity of evidence on impacts related to social and cultural wellbeing suggested an aggregate assessment at the endpoint level. Endpoint impacts are the highest level of aggregation, and as such, they include wide-ranging issues, restricting the level of detail in the assessment, but still providing some guidance on the direction of impacts.
Table 3 Wider impacts considered
|Wider impact||Type of impact|
|WI1||Air quality: NH 3||Direct|
|WI2||Air quality: NO x||Direct|
|WI3||Air quality: PM||Direct|
|WI4||Air quality: other||Direct|
|WI5||Water quality: Nitrogen leaching||Direct|
|WI6||Water quality: Phosphorous leaching||Direct|
|WI7||Water quality: other (e.g. pesticides)||Direct|
|WI9||Flood management, water use||Intermediate /Direct|
|WI10||Land cover and land use||Direct|
|WI12||Animal health and welfare||Direct|
|WI14||Household income (income effects and distribution of impact)||Direct|
|WI15||Consumer and producer surplus||Direct|
|WI16||Employment (type and number of jobs)||Direct|
|WI19||Social impacts (cohesion, social engagement)||Endpoint|
|WI20||Cultural impacts (recreation, spiritual, cultural heritage, landscape value)||Endpoint|
This study used a rapid evidence review methodology, consisting of a literature review, which included peer-reviewed publications and grey literature (reports produced by national, international and third party organisation). International literature was considered for its applicability in a Scottish context. Where direct evidence was not available expert judgement was used, stating the likely importance of the WI.
The summarised evidence attempts to cover the most important aspects of the GHG MOs, highlighting trade-offs and synergies without covering the finer details of spatial and temporal variations or the heterogeneity of biophysical constraints or agricultural management; all of which might change the magnitude or direction of the impacts. However, significant dependencies of this kind are highlighted in the report.
Some MOs cover a range of different practices on farms (e.g. renewable energy, low emission storage and application of manure, improving livestock health). Here general impacts are presented noting the key specific impacts. Similarly, the WIs are often composites of very varied impacts; for example cultural impacts include recreational, educational, spiritual and aesthetic aspects. The assessment of these WIs offers a high level overview, with highlight of specific issues (e.g. the recreational impact of afforestation is discussed in more detail).
Beyond providing a short explanation on the processes resulting in the WIs in relation to the MOs, each WI of each MO is scored at a 5-level scale (from strong positive to strong negative effect), while the evidence available was rated as weak, moderate or robust.
The MOs and the WIs are not directly comparable at an aggregated level based on the presented results, i.e. a MO with three positive effects is not necessarily more desirable than another MO with two positive effects (all other things being equal). This is at one hand because a 5-level scale can only distinguish positive and strong positive effect, meaning that there can be considerable difference between two impacts assessed equally. More importantly, the assessment only considers the physical impacts without converting these to impacts on human well-being. Additionally, as the WIs evaluated relate to different impact-levels, the interrelations between them (e.g. NH 3 emissions having an impact on human health) means that some aspects are considered more than once in the qualitative assessment. This double counting should be avoided before any aggregated quantitative analysis to be done.
Available tools for the assessment of the WIs in relation to the MOs were also reviewed, providing short description of models and tools that could (or have been) used to assess the WIs at the national level.
Email: Debbie Sagar