Agriculture bucks NI trend in GHG emissions

Despite relatively static cattle numbers for over 30 years and a halving in the amount of artificial fertiliser being spread, the greenhouse gas (GHG) emissions attributed to agriculture in NI are up 14.9% since a 1990 base year.

The only other part of the NI economy to have higher emissions is domestic transport, with more vehicles on the road, resulting in a 7.1% increase in emissions when compared to 1990.

Emissions from ‘buildings’ are down 29.1% due to the use of less carbon-intensive heating systems in properties, while the shift away from oil and coal-fired power stations has seen emissions from electricity supply down by 43.9%.

As a result, the share of total NI emissions attributed to agriculture is steadily increasing to now stand at 29%.

Unless the accounting system is amended, this share is only going to get higher, given that other sectors of the economy are easier to decarbonise.

For example, if NI motorists can be encouraged into electric cars, it will significantly reduce the figures for domestic transport.

Excluded

However, it is valid to question whether the current accounting system used is fair, especially for agriculture.

For example, the UK / NI figures exclude emissions associated with production of goods and services the UK imports from other countries.

In other words, what is published in the national inventory are territorial emissions covering those that occur within UK borders.

This accounting system suits various parts of the economy, especially those that increasingly rely on bringing in goods from overseas.

The same principle applies to imports of grain used in animal feed. As a result, intensive sectors such as pigs and poultry have a low carbon intensity in NI.

However, in general, the principle works against NI agriculture as it is a major exporter of food.

Our figures would look very different if production-based emissions applied where the food is consumed, not where it is produced.

Shown in Table 1 are the five main sources of agricultural emissions, which collectively account for over 95% of the agriculture total.

Methane, which is a potent GHG produced by cattle during the rumination process, makes up over half of NI agricultural emissions.

As a result, much of the current research focus is on feed additives that might reduce methane output.

But is this enteric methane properly accounted for in the current system, given it is part of a natural cycle? Methane released into the atmosphere is broken down into carbon dioxide, which is taken up by plants (sequestered) which are then eaten by cattle.

It is fundamentally very different to the burning of fossil fuels, yet the current accounting system gives both an equal weighting. There is a growing acceptance among the research community that a new metric (GWP*) should be used to assess the global warming potential of methane from ruminants.

Under GWP*, where a national herd is stable, the methane released today is simply replacing that released 10 to 12 years ago, so there is limited impact on the climate. But where methane emissions are rising, GWP* clearly shows this additional methane is contributing to global temperature rise.

For NI agriculture, switching over to using GWP* will only be of significant benefit if we can get methane emissions down.

Wrong direction

At present, the data suggests methane is generally going in the wrong direction. Compared to 1990, methane emissions from cattle are up over 20%. Yet, as shown in Table 2, cattle numbers in 2022 were just 3.8% higher than in 1990, so why the significant disparity? On enquiry, a DAERA spokesperson confirmed that the increased methane from ruminants is because of a switch from sucklers towards dairy since 1990.

“There has been a significant increase in dairy cow numbers of 14% (278,000 to 317,000), with non-dairy cow numbers increasing by only 2% (1,348,000 to 1,370,000). The enteric emissions associated with dairy cows are much larger than for most non-dairy cow animals,” said the spokesperson.

“In addition, an increase in dairy cow feed intake (helping to support higher milk yields) has also been a factor,” the spokesperson added.

Soils

Behind methane from cattle, the next major contributor to agricultural emissions is from the soil, although this is down 12.9% since 1990.

Included within this are emissions related to artificial fertiliser use, with nitrous oxide (a potent GHG) released when fertiliser is spread.

Over the period, NI farmers have cut fertiliser use virtually in half (469,900t to 250,400t), so why is this figure for soil emissions only down 12.9%?

According to the DAERA spokesperson, the drop in emissions from artificial fertilisers has been partially offset by increases in the amount of manure applied to soil and by the use of organic fertilisers, which were not recorded back in 1990.

Waste

Third on the list of agricultural emissions are those linked to cattle wastes, with a 13.3% share of the agricultural total.

While cattle numbers are up 3.8% since 1990, the data published by DAERA suggests emissions from cattle wastes are up by 40.9%.

“Again, the rise in dairy cows has been accompanied by an increase in overall cattle waste,” responded the DAERA spokesperson.

Fuel

That leaves ‘stationary and mobile combustion’ as the fourth largest contributor, with emissions that have increased over 60% since 1990. This category includes the likes of fuel used in equipment and to heat buildings, such as intensive poultry units.

The last category listed in Table 1 is methane from sheep, which has fallen 23.9% since 1990 on the back of a 26% reduction in numbers since then.

2022 farm emissions fall by 1.7%

Latest figures from DAERA indicate that greenhouse gas emissions from the NI agriculture sector fell 1.7% during 2022.

According to the department, the drop “was primarily due to reduced emissions from off-road machinery as a result of less favourable growing conditions for cereals and other crops”. Another “significant contributory factor” was the reduction in nitrogen fertiliser use during 2022. Across all sectors of the NI economy, emissions were down 3% in 2022 compared to the previous year.

The NI climate change act passed in 2022, requires emissions to get to net zero by 2050.