At COP26 in Glasgow it was announced that more than one hundred countries have signed up to a global methane pledge, agreeing to cut emissions by 30% by the end of the decade.

Commenting from COP26, NFU Scotland’s Climate Change Policy Manager Kate Hopper said: “Scottish farmers, crofters, and growers are already on their net zero journey and have a key role in further reducing emissions to meet climate change goals of net zero greenhouse gas emissions by 2045.

“The Scottish beef industry has a greenhouse gas footprint that is half of the world average and has reduced methane emissions by 18 percent 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 3,000 megatonnes of carbon and Nitrous Oxide emissions from fertilisers, soil cultivation and manure management have fallen by 15 percent as farmers have moved to more organic methods.

“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.  More importantly, the way we include methane in our emission calculations must change.

“In Scotland, agriculture is responsible for 7.5 MtCO 2e of GHG emissions, of which methane accounts for 4.4 MtCO 2e. Methane is a greenhouse gas of concern as it is 28 times more potent in its warming potential than CO2. The potency of greenhouse gases is compared using a metric called Global Warming Potential 100 (GWP100) which compares the impact of a GHG over a 100-year period.

“However, GWP100 is outdated and does not consider the natural methane cycle. 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. 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. Methane does cause warming, but it is a flow gas and 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. 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 3 to 4 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. 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.”