The global warming impact of methane emissions from Irish livestock is being vastly overestimated under the current accounting system used by the Environmental Protection Agency (EPA).

The Irish Farmers Journal has carried out a detailed analysis of the warming impact of Irish methane emissions using the GWP* metric developed by world-renowned climate scientist Prof Myles Allen from Oxford University.

This analysis shows the warming impact of methane from Irish livestock is only a fraction of what has been suggested, and that lower methane levels from Irish livestock have actually contributed to global cooling over much of the last decade.

The Irish Farmers Journal analysis shows that methane emissions in Ireland for 2018, almost all of which come from agriculture, stood at just 0.5m tonnes of CO2 equivalent.

[...] the global warming impact of methane produced by Irish livestock was just 0.5m tonnes of CO2 equivalent and not the 13m tonnes of CO2 equivalent implied by the EPA figures

This figure is almost 25 times lower than the figure currently used by the EPA for the global warming impact of methane from Irish livestock.

Using the GWP100 accounting system for methane, which assumes that 1t of methane is equal to 25t of CO2, the latest EPA report states that methane emissions in Ireland stood at 13m tonnes of CO2 equivalent, which is a vastly higher number than that calculated using the GWP* metric. In simple terms, this means that the global warming impact of methane produced by Irish livestock was just 0.5m tonnes of CO2 equivalent and not the 13m tonnes of CO2 equivalent implied by the EPA figures.

The disparity in methane emissions between both accounting systems is even more pronounced when we look at figures for the last decade (see Figure 1).

In 2017, the EPA reported that Irish methane emissions again stood at just under 13m tonnes of CO2 equivalent.

However, under the GWP* metric, Irish methane emissions in 2017 were just over 1.1m tonnes – which is 12 times lower than the EPA’s figure.

And if we look at methane emissions figures for the first half of the last decade, the GWP* metric shows that lower methane emissions from Irish livestock actually contributed significantly to global cooling from 2010 to 2014. During that period, Irish cattle numbers were significantly lower when compared to 20 years previously.

Global cooling

From 2010 to 2014, Irish livestock farmers actually helped remove over 9m tonnes of CO2 equivalent from the atmosphere because there were lower methane emissions in those years relative to the 1990s (see Figure 2).

In 2011 alone, Irish livestock helped remove over 3.1m tonnes of CO2 equivalent from the atmosphere, because the national herd was producing less methane relative to 20 years previously. However, using the GWP100 metric, the EPA estimated that Irish methane emissions for 2011 were 11.3m tonnes.

Our traditional accounting system undervalues the impact of changing rates of methane

The analysis carried out by the Irish Farmers Journal shows that the current GWP100 method recommended by the IPCC and being used by the EPA and other regulatory bodies to calculate the global warming impact of methane delivers very different outcomes and is not accurate according to Prof Myles Allen. As can be seen, the disparities in both sets of figures for methane are enormous.

The figures calculated in this analysis using the GWP* methodology have been verified by multiple climate scientists, including Prof Myles Allen and his team at Oxford University.

“Our traditional accounting system undervalues the impact of changing rates of methane. For example, if someone sets up a new fracking operation that results in new methane being released into the atmosphere and they are being undercharged for the warming impact of that new methane,” says Prof Allen.

“Conversely, if you take a source of methane emissions that is steady, like a herd of cows that has been around for a century or more then the impact of those cows is being overstated.

“It’s like a double own goal. Under the current equivalent system, that herd of cows is only causing 25% of the global warming that is implied by the CO2 equivalent emissions,” he added.

Implications for Irish farming

The implications of using the more accurate GWP* metric to calculate the warming impact of methane emissions are profound for Irish agriculture.

Under this metric, the total emissions from Irish agriculture in 2018, including emissions from soils, slurry and other sources, stand at less than 9.6m tonnes, which is more than half the level reported by the EPA last year (20.5m tonnes).

Agriculture’s share of the total emissions for 2018 drops to 19%

The GWP* metric also means that Irish agriculture is no longer the sector with the largest emissions profile in the Irish economy. Instead, transport contributes the largest amount of emissions in Ireland, accounting for 25% of total emissions. Agriculture’s share of the total emissions for 2018 drops to 19%.

Again, the disparities are significant. Under the EPA’s current accounting inventory, agriculture accounts for 34% of all emissions in Ireland.

Cooling effect

Looking back at 2011 when lower methane levels were delivering a cooling effect, agriculture accounted for just 9% of Ireland’s total emissions as emissions from farming stood at just 4m tonnes using the GWP* accounting metric.

It should be noted that while Prof Allen has developed the GWP* metric to be a much more accurate accounting system for the global warming impact of methane, it is not a get out of jail free card for Irish agriculture.

Instead, the metric highlights the hugely positive impact agriculture can have on the planet with lower methane emissions.

This means Ireland will have to monitor cattle numbers going forward, as GWP* does not allow for unlimited expansion in dairy cow numbers.

Given that Irish cattle numbers began to decline from 2001 onwards (see Figure 2), the GWP* metric will reflect that when calculating methane emissions figures in the years ahead.

In simple terms, as long as Ireland’s cattle herd keeps in line with, or below, the level it was 20 years ago, then the warming impact of methane produced by Irish livestock is actually quite low.

the GWP* metric also shows the significant cooling impact lower methane emissions can have

However, if Irish cattle numbers start to rise higher than where they were 20 years ago then the methane produced by those extra cattle will have a significant global warming impact and this will be reflected in the numbers calculated under the GWP* metric.

Additionally, the GWP* metric also shows the significant cooling impact lower methane emissions can have and amplifies the potential benefits a methane-reducing feed additive for cows could have on our climate.

Prof Myles Allen argues that the value of reducing methane could place a new capital value of €5,000 per head for a farmer reducing cattle numbers

As stated already, the lower methane levels in Ireland in 2011 helped remove almost 4m tonnes of CO2 equivalent from the atmosphere.

This creates potential for ambitious carbon trading schemes and means that farmers who reduce their total cattle numbers on the farm or introduce methane-reducing feed supplements could receive significant compensation.

Prof Myles Allen argues that the value of reducing methane could place a new capital value of €5,000 per head for a farmer reducing cattle numbers.

Additionally, if we include the carbon sequestration potential of grasslands, hedgerows and trees on Irish farms, which has been conservatively estimated at up to 9m tonnes of CO2 per annum, then the net impact of Irish agriculture in terms of carbon emissions is very modest.

Professor Myles Allen from Oxford University wants the European Commission to change how it calculates methane emissions to the GWP* metric he developed. \ Simon Hadley

Given the importance of agriculture to the rural economy in Ireland, it is essential that Irish Government policy is changed to allow the EPA to adopt the GWP* metric as the method for calculating the global warming impact of methane. The IPCC also needs to adapt its methodology for calculating GHG emissions to include the GWP* metric.

Not only will adopting GWP* allow for a far more accurate measurement of the impact of livestock on global warming, says Prof Allen, but it will also create a fair playing field for Irish farmers to meet the climate targets set by the Irish Government and the EU up to 2030 and beyond.

What are GWP* and GWP100?

In order to make it easier for policymakers to understand climate science, the Inter-governmental Panel on Climate Change (IPCC) has set global warming potential (GWP) values for all greenhouse gases. These figures are all relative to carbon dioxide (CO2), which is the main gas associated with man-made climate change.

The GWP100 metric is used to compare the global warming impact of different greenhouse gases over a 100-year period – hence GWP100.

Methane is a highly potent greenhouse gas and has a warming impact about 25 times that of CO2. Under the GWP100 metric, this assumes 1t of methane is deemed to cause as much warming as 25t of CO2 over 100 years. However, comparing the two gases in this way has caused problems because C02 and methane behave very differently in the atmosphere.

While methane has a much stronger warming impact, its lifetime in the atmosphere is much shorter than C02, which stays around for centuries. Instead, methane is destroyed after about 12 years.

In simple terms, GWP* is a far more accurate metric to measure the global warming impact of methane

Because of this significant difference in the lifecycles of C02 and methane, Prof Myles Allen and his team at Oxford University developed the GWP* metric to better reflect the global warming impact of methane and its shorter lifespan.

In simple terms, GWP* is a far more accurate metric to measure the global warming impact of methane, according to Professor Allen, because it measures the new methane being produced by livestock or fossil fuel companies today but it also takes into account the methane created 20 years ago that is now leaving the atmosphere.

Once the methane levels of today are in line with or below the level they were 20 years ago, the GWP* metric will accurately show a much lower impact for these methane emissions. However, if methane emissions today are higher than where they were 20 years ago, the GWP* metric will also more accurately reflect the major warming impact this will have on the climate.

Is GWP* being used by regulators?

At present, regulators are not using the GWP* metric to account for methane emissions.

However, Professor Myles Allen made a submission to the European Commission in August, urging it to begin using the GWP* metric as a more accurate measure of the impact of methane.

In Ireland, the EPA is the body charged with compiling data on Ireland’s climate emissions each year.

The EPA is currently using the GWP100 metric recommended by the IPCC to calculate methane emissions in Ireland.