Project P3: Clarifying the greenhouse gas emissions (carbon footprint) associated with different growing media – is examining how to build on scoping work funded by Defra on how to define and measure the carbon footprint of different growing media.

Project description

Defra has funded initial exploratory research on this topic which raised more questions than it answered. These were particularly in relation to the methodology which can be used to determine the carbon footprint of organic materials that changes bulk density during their lifetimes, are a mixture of virgin materials, bi-products and waste materials, and are not the final end product (which would be the plant grown). Further research is required to produce more robust data, however, before any new research can be commissioned the Task Force first needs to address and agree methodological points and boundary issues for this research.

Project Lead: Judith Stuart (Defra)

Dependencies: P1 – if greenhouse gas emissions are not identified, in the first instance, as part of the problem then this work is not required. Although this project will also contribute to determining if greenhouse gases are, ultimately, part of the issue of concern.

Deadline: This is a longer term project.

Progress/Update

At a project group meeting in January 2012, it was proposed that whilst the carbon footprint of growing media was retained as part of the narrative the work going forward should focus on tracking the footprint trend of growing media (relative change) rather than coming up with absolute numbers for the carbon footprint of different materials and products.

It was judged that the level of variability inherent in the system (variable bulk densities, carbon contents, greenhouse gas emissions from different methods of producing materials) made generic approaches to carbon footprinting less useful. However, the greatest weakness in the approach to carbon footprinting was on the agreement of boundaries and underlying assumptions (about the materials and different stages in the life cycle). It would not be possible to undertake carbon footprinting without the use of assumptions as it was not possible to model every situation. Once agreement was reached on the assumptions it would be possible to do research to refine the emissions in the footprint. However, whilst any single group could come up with an agreed set of assumptions (although this would not be simple), the assumptions of one group would be open to challenge by others who were not party to that agreement. Therefore, any other group could produce a different carbon footprint for the same materials and products, which would be equally valid within the assumptions they used.

It had been hoped that carbon footprinting would remove the emotion from the debate, with numbers being easier to discuss. But as all numbers would still be open to challenge and the methodology complex (and costly) it was questioned whether this was the correct approach to take at all. We could put a lot of effort and resource into this without actually getting anywhere useful and without enough clarity to use carbon footprinting in differentiating between growing media on the basis of greenhouse gas emissions and to guide work on reducing the carbon footprint of growing media. Moreover, carbon footprinting was actually clouding the issue and making it a very emotive issue. It had the potential to get in the way of what we were trying to achieve.

Everyone agreed that it was hard to see how we could go forward without acknowledging greenhouse gas emissions. However, due to the significant uncertainty in the definition of boundaries and assumptions, it was not possible to come to a definitive position on the carbon footprint of different material.

Although the proposal to not take forward work on carbon footprinting of growing media was counter-intuitive it was generally endorsed by the Task Force at its 1 March 2012 meeting. However, an assessment of the climate change impacts of growing media (e.g. impact on carbon sinks) is required and it was proposed that a simple measure of this was included in the sustainability assessment being developed under project P4.

Unrelated to the work of the Task Force the European Peat and Growing Media Association (EPAGMA) has recently published research on a ‘Comparative life cycle assessment of horticultural growing media based on peat and other growing media constituents’. This is available on the EPAGMA website.