Methane emissions from livestock higher than thought – except in Europe

The internationally recognised way of measuring the contribution of livestock to climate-altering methane emissions is according to guidelines published in 2006 by the International Panel on Climate Change (IPCC). However, this method is “based on literature reflecting earlier decades” and “no longer reflects the state of livestock,” Julie Wolf of the US Department of Agriculture, Ghassem R. Asrar of the University of Maryland’s Joint Global Change Institute and Tristram O. West of the US Department of Energy explained in the academic journal, Carbon Balance and Management.

Changes in farming practices including feeding, manure management and breeding, which in turn influence milk and meat productivity and animal body mass, all influence emissions of the greenhouse gas. The authors of the study used the most recent data on these factors to update existing estimates of methane (CH₄) emitted by livestock.

North American emissions highest

Using 2011 as a reference year for the entire planet, “this quantity is 11% greater than obtained using the IPCC 2006 emission factors, encompassing an 8.4% increase in enteric fermentation CH₄ and a 36.7% increase in manure management CH₄, with notable variability among regions and sources”.

The new calculation found livestock methane emissions from the US and Canada to be 24.2% higher, and the highest of any region in the world. However, there was no significant difference in revised figures for Europe, or for east and south-east Asia. Emissions from other regions of the world were found to be 10% to 15% higher than under the IPCC calculation.

Western Europe

On a per head basis, the study found that the rumens of western European lactating cows emit 11.6% more methane than previously thought. While the region remains among the highest emitters of methane per cow, the revised estimates found that east Asian cows were.now more greenhouse gas-intensive than European ones.

Meanwhile, each beef or non-lactating dairy animal in western Europe turned out to emit 18.4% less methane from enteric fermentation than previously thought. This places them among the most carbon-efficient in the world.

The study also revised down emission estimates for all cattle in eastern Europe.

These estimates are calculated per head of cattle, the unit multiplied by livestock numbers to obtain national emission figures. They do not reflect milk or beef yield, which would be required to measure the carbon intensity of dairy or meat output.

Feedlots and lagoons

The scientists point to a number of evolving practices in regions where emissions are revised up, including increasing the rearing of cattle in feedlots and management of manure in long-term lagoons rather than spreading it on land. These would reinforce the Irish Government and farming organisations’ arguments that grass-based cattle farming releases less methane into the atmosphere.

The study also showed western Europe to be the only region in the world where methane emissions from pig slurry were lower than in IPCC estimates.

The study was published as the Citizen’s Assembly began discussing how Ireland can become a leader in tackling climate change at the weekend. The first two days of debates on the topic focused on general presentations on the issue and energy policy, with further discussions and recommendations scheduled on 4 and 5 November.

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