The complexities of measuring a farm carbon footprint
Calculating the carbon footprint of a farm is a complex problem
Calculating the carbon footprint of a farm is a complex problem.
There are various units of measurement that we could use on farm – emissions per kg of output, emissions per calorie of output, emissions per farm, emissions per hectare. They all have different purposes, and their impact depends on why a footprint is being completed and how that data is used.
There are two broad approaches taken for emission assessments – product level and farm level. The Greenhouse Gas Protocol provides guidance on both.
Product level carbon footprints
Product level assessments calculate emissions through a system from cradle to grave ideally, although often taken to the farm gate. These would be the footprint of a tonne of grain, per kg liveweight beef or per litre of milk. It is possible to look at emissions per hectare to understand the combination of emissions intensity (emission per tonne) and absolute emissions (total emissions from the land used to produce the product).
When calculating these emissions, focus only on those activities that relate to the production of that particular output. For example, with grain, focus on the field that produces the grain (excluding activities on the surrounding farm – producing other crops, livestock or managing woodland). With the production of beef, follow the animal from conception (i.e. its parental emissions) through calving to slaughter. This is challenging where cattle are sold on and off farm at different stages of life.
Product level assessments should include:
- all raw materials used to produce the products (manufactured fertilisers, pesticides, medicines, feeds etc.)
- the emissions that occur on farm (nitrous oxide from nitrogen applications, methane from livestock, carbon dioxide from
combustion of fossil fuels) - the emissions from imported energy (electricity or heat) used specifically to make the product.
The advantage of product level carbon footprints
The advantage of product level assessment is that it creates a footprint for the whole supply chain. For example with wheat, the wheat footprint passes through the distributor (adding transport emissions), through to the miller (adding energy emissions from milling), to another distributor (more transport), to the baker (adding more ingredients and energy for baking, plus packaging), through more distribution and retail to the consumer (adding more energy and transport).
So the farm level product footprint is one brick in a chain that cumulatively adds emissions to the footprint of the product. What should and should not be included in a product footprint is set out in the GHG protocol product standards.
Farm level carbon footprinting
Farm level carbon assessments are more open to interpretation. The first step is to clearly define the boundary of farm level footprint, and this depends on the goal of the assessment. The main guidance would be GHG protocol organisational footprinting guidance – this sets out how to assess an organisation and what to include.
However, farms are really complex and may contain multiple interconnecting enterprises, including agricultural, diversification, forestry etc. Agricultural enterprises may interconnect – for example straw from one providing bedding for another, which provides organic manure to the first.
There is currently no single standard that sets out how to conduct a farm carbon footprint. Instead, there is generic guidance for organisations, plus supporting guidance on how supply chains might deal with farm level assessments in the form of:
- the Science Based targets initiative (SBTi)
- Forestry Land and Agriculture Guidance (FLAG)
- the Land Sector and Removals Guidance from GHG protocol
None of these are specifically targeted at the farmer, more the industries that are interacting with the farmer. They do however dictate what to assess as scope 1 (on farm emissions), scope 2 (emissions from imported energy) and scope 3 (embedded emissions).
The advantage of farm level carbon footprints
These farm level assessments can potentially demonstrate how the whole farm is performing across rotations or the whole production system is performing in terms of emissions and removals. It brings in greater opportunities to include removals from non-productive areas of the farm (woodlands, hedgerows etc).
Creation of a standardised metric
Having a hard and fast metric is not necessarily helpful – as different users may need footprints of different things calculated in different ways for different purposes. Instead, farmers need clearer, more specific guidance as to what a ‘farm level’ carbon footprint should include and exclude (in terms of activities on farm), and how to use a farm level assessment. This would increase understanding of what is being measured and why, and ensure that any calculation tools are aligned to a standardised boundary.
Gaps in current knowledge
It is important to realise that creating a carbon footprint in agriculture is a modelling exercise – it is taking complex biological systems and boiling them down to simple systems and assumptions. A clear example of this is the approach to modelling soil carbon.
Soils are highly diverse in their composition and structure, as well as the practices that have been used historically to manage them. They also respond slowly to changes in practice, especially regarding the accumulation of carbon. Trying to create a simplified model to quantify how these biological processes accumulate or lose carbon will either require significant amounts of data, or include massive assumptions that result in high levels of uncertainty in the results. We generally have good understandings of what practices will lead to reductions in emissions or increases in sequestration. The ability to accurately quantify is much more challenging.
A way to identify opportunities
Calculation of carbon metrics is not as an absolute measure of emissions. Rather, it is a process of identifying opportunities for reducing emissions and estimating the potential scale of reduction possible from the adoption of new practices or technologies.
The industry needs to recognise that, because everything is modelled, there is no ‘correct’ value. Science will evolve in the quantification of emissions. However, the guidance around the practices to implement and the opportunities for emission reduction or increase removals are well understood, and unlikely to be significantly affected by updates to measurement approaches.
ADAS Managing Director of Climate Change and Sustainability Sarah Wynn authored this piece in response to the publication of the Defra commissioned report on Harmonisation of Carbon Accounting Tools for Agriculture.