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There is a growing consensus among climate scientists that the current way of measuring methane emissions from ruminant livestock systems could be overestimating the impact of methane on global warming potential.

We explain how beef and lamb from Grassroots farms meets both reporting frameworks.

The debate has arisen due to the current units which estimate the impact of the gases over 100 years. This metric works well for Carbon Dioxide and Nitrous Oxide, as once this gas is released into the atmosphere it remains there at the same concentration until it is removed.

Methane, however, is classified as a short lived climate pollutant; as such it behaves differently to carbon dioxide and nitrous oxide.

Once methane is released it has an initial pulse where it has a significant warming impact, however after between 9 and 12 years this warming impact is reduced as the gas breaks down and is reabsorbed back into the environment.

For example, consider 1 tonne of both methane and carbon dioxide that were released 30 years ago; the carbon dioxide is still present in the atmosphere and having a warming impact, but the methane has dissipated and is having no effect.

If methane rates can be stabilised then it will not cause an increase in global temperature.

This work has been pioneered by academics and scientists at Oxford Martin School of Oxford University, including Professor Myles Allen and Dr Michelle Cain and has led to the development of a new metric for assessing methane, GWP*. A summary of their work in this area can be viewed here.

This work has very much been focussed on the issue of global livestock numbers and their impact on global temperature rise; as such there is a need to translate these global forecasts into something that is meaningful for individual farm footprints.

Currently this is being developed and as such, within Grassroots Carbon Supply Chain calculations there is the ability to understand how this shift to the new GWP* will impact each farm’s footprint.

In order to calculate GWP* it is important to be able to a more nuanced approach to farm emissions.

We separate livestock emissions into enteric emissions (arising from methane) and manure emissions (which are split between methane and nitrous oxide).

Once the split is calculated, this is then combined with farmer information on livestock numbers (whether they are growing, static or declining) to form an assessment as to whether GWP* can be applied.

If the livestock numbers are static or declining then the methane is not contributing to global temperature rise, as such, the methane emissions from livestock are removed from the calculation. As a general rule this constitutes 75% of livestock emissions.

There is recent progress on adoption of GWP* in the UK.

The AHDB and the NFU have recently spoken out about the need for the government to implement GWP* for measuring emissions from livestock. Currently the UK Net Zero legislation, carbon budgets and targets are all assessed against GWP100, however there is increasing focus on utilising a more nuanced metric for methane.

This debate is currently underway and there are discussions ensuing with Defra as to the way forward.

Beef & Lamb from Grassroots farms comes with a CO2E per kg of product for both GWP100 and GWP*.

Currently Grassroots Farming produce dual reporting of carbon footprints for their customers - showcasing the carbon footprint using traditional metrics (GWP100) and then also reporting against GWP*.


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