In 2018, emissions from Ireland’s agriculture sector rose 1.9% to 20.6m tonnes of CO2 equivalent (eq). Of this, enteric fermentation, or methane produced by cattle and sheep, accounts for more than half (56%) of all agri emissions, or just over 11.5m tonnes of CO2 eq.

However, new research emerged last year from Oxford University in the UK which challenges the approach used by the Intergovernmental Panel on Climate Change (IPCC) to calculate methane emissions.

Up to now, the IPCC has set global warming potential (GWP) values for all greenhouse gases. These figures are all relative to carbon dioxide (CO2), the main gas associated with man-made climate change.

Although it’s a short-lived gas (circa 12 years before it breaks down), methane is highly potent and about 28 times more damaging to the earth’s atmosphere than CO2. This means 1t of methane is deemed to cause as much warming as 28t of CO2.

However, the 2018 report published by Oxford-led academics suggests that methane is misrepresented in the IPCC’s climate calculations. The report states that, because of its short life-span, the concentration of methane in the earth’s atmosphere should be calculated differently to CO2, which can remain in the earth’s atmosphere for centuries.

In simple terms, the Oxford report found that, unlike CO2, methane increases global warming only if its emissions increase. If they remain stable, there are no further global warming effects. If methane emissions reduce, this has a cooling effect on the planet. In contrast, if CO2 emissions remain stable each year, they are still adding to global warming because of the cumulative effect of CO2 gathering in the atmosphere (see graph).

The Oxford report called for a new metric called GWP* to be used in calculating methane emissions to allow for more informed and fairer government policies on climate change, particularly in relation to targets for agriculture.

“The conventional Global Warming Potential (GWP) can be misleading when applied to methane emissions, particularly when these are being reduced. A revised usage of GWP, denoted GWP*, which uses the same metric values interpreted in a new way, provides a more accurate indication of the impact of short-lived pollutants on global temperature,” the Oxford report stated.

Accurately measuring methane is very important for agriculture, particularly for livestock farmers. If livestock numbers are the same as a decade ago and methane emissions are the same every year, then farmers are not contributing to global warming because the methane being produced by cattle and sheep this year is simply replacing the methane first produced a decade ago. Effectively the amount of methane in the atmosphere holds steady.

And if methane emissions begin to reduce it will have a significant cooling impact on the atmosphere.

However, if methane emissions are rising they will have a substantial warming effect, equivalent to large emissions of CO2.

In a global sense, agriculture accounts for 24% of all methane emissions, while extraction of fossil fuels such as oil and gas accounts for 20% of global methane.