REDUCING methane emissions has been put front and centre during the first week of COP26 – but how those emissions should be measured is still a subject of disagreement.

More than 80 countries have signed up to a global methane pledge to cut emissions of the gas by 30% by the end of the decade. Implicit in this effort will be renewed attention to the methane released by livestock production.

Read more: Dairy crossbreeding can cut methane emissions

But Scottish farming leaders were quick to highlight that, in comparison with intensive systems elsewhere in the world, Scotland's livestock industry is already an exemplar of how to produce high quality – but low methane – meat and dairy products.

NFU Scotland’s climate change policy manager, Kate Hopper, said: “The Scottish beef industry has a greenhouse gas footprint that is half of the world average and has reduced methane emissions by 18 % in recent times. The carbon footprint of our milk is one-third lower than the world average. Scottish soils, which are grazed by cattle and sheep, hold a staggering 3000 megatonnes of carbon, and nitrous oxide emissions from fertilisers, soil cultivation and manure management have fallen by 15% as farmers have moved to more organic methods.

Read more: Better genetics are the key to lower livestock emissions

“While there is a lot more work to do, the Scottish public can be reassured that, with COP26 taking place in Glasgow, Scottish agriculture is making positive strides towards meeting its targets and responsibilities and that includes methane and, more importantly, the way we include methane in our emission calculations," said Ms Hopper.

As a greenhouse gas, methane is 28 times more potent in its warming potential than carbon dioxide, when compared using the currently dominant metric of Global Warming Potential 100 (GWP100) which calculates the impact of a GHG over a 100-year period.

However, Ms Hopper suggested that GWP100 was 'outdated' and does not consider the natural methane cycle.

Read more: Scottish Ag leaders raise farming's needs ahead of COP26

"Biogenic methane (which comes from cattle) is a flow gas which degrades in the atmosphere into CO2 through a natural cycle, compared to a stock gas (like CO2) which does not," she explained. "A flow gas stays stagnant because it decreases at the rate that it is emitted. The methane is recycled into atmospheric CO2, which is then used by plants, and in turn ruminants. Because methane is a flow gas, it has a half-life of 12 years compared to CO2’s half-life of 50 to 200 years.

“A new methodology to properly take this into account has been proposed by the University of Oxford and is supported by NFU Scotland," she said. "This is called ‘GWP*/GWP-we’. The new methodology provides a more accurate measure of the behaviour of methane in the atmosphere and its net contribution to global warming. This is also recognised in the latest Intergovernmental Panel on Climate Change (IPCC) report which states 'Expressing methane emissions as CO2 equivalent emissions using GWP100 overstates the effect of constant methane emissions on global surface temperature by a factor of three to four over a 20-year time horizon'.

“Using GWP*/GWP-we to assess the impact of methane emissions is the first step in understanding the full picture of the impact of ruminants and the steps needed to be taken to reduce the impact of methane in Scotland," said Ms Hopper/. "This includes the use of genetics, feed management, and efficient finishing of animals for the marketplace, alongside increased carbon sequestration and soil, crop and biodiversity management on farm.”