A report dealing with the greenhouse gases associated with peat and peat alternatives (e.g. coir, wood fibre, bark, green compost) was published last week by Defra (download a copy here).
This project sought to measure and compare the greenhouse gas emissions (basically the carbon footprint) associated with different growing media materials. Predictably the answers found varied depending on the methods used to measure them. The main difference in the methods used hinges around whether or not you take account of how ‘renewable’ the growing media material is. Peat is generally argued to be non-renewable, akin to a fossil fuel, so its ‘end of life’ adds carbon dioxide to the atmosphere. By comparison, other materials like green compost, bark, wood fibre and coir are renewable and their ‘end of life’ can be considered carbon neutral.
Using a Life Cycle Analyses approach (this includes all emissions that contribute to global warming and as such doesn’t penalize or give credits on the basis of ‘renewability’ of the product), the Defra report shows that coir, UK peat and Irish peat actually have a smaller carbon footprint than green compost and bark. When ‘weight’ is used in the calculations (as opposed to ‘volume’), coir, UK peat and Irish peat also have a smaller carbon footprint than wood fibre.
However, using an ‘offset’ approach (where renewability of the product is taken into account), the report shows the opposite to be the case – peat (irrespective of where it is sourced from) predictably has a higher carbon footprint than bark, wood fibre, green compost and coir.
It would be easy to say the report reaches no meaningful conclusions, but actually the results are useful, and meaningful conclusions can be drawn. This project was challenged by limited and variable original data, the problems of using weight or volume as unit of measurement, and the different methods you can use to measure carbon footprints. However the results still provide a useful indication of the greenhouse gases associated with peat and other growing media materials. It has long been an NFU hobby horse that no peat alternative should impose a greater environmental burden than peat use itself. In terms of carbon footprint, the Life Cycle Analysis used in this report has found that some peat is more sustainable than some peat alternatives.
The most meaningful conclusion of this project is that, because of the difficulties outlined above, the evidence-base is not robust enough to justify using CO2 emissions as a reason to drive reduced peat use. Considering this, and that Defra have had these results in-hand since February 2009, how is it that a Defra Minister launched an ‘Act on CO2’ campaign in March of this year that aimed to wean gardeners off peat by 2020 on the basis that they ‘can lower their CO2 emissions immediately by using peat-free compost’?
This project had restrictive objectives and scope, which from the start limited what it was able to achieve. When this project was first proposed the NFU questioned the value of the work if it did not actually compare end-products of comparable performance. Is it good enough to be able to say material A has a lower carbon footprint than material B, when the reality is that you can’t successfully grow anything in material A without adding loads of inputs that each bring additional carbon footprints into the equation?
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