‘It is not new carbon that we have; it is recycled carbon’ – Dr. Mitloehner on livestock-related emissions

Livestock emissions are “completely different” than fossil fuel emissions. This is a key message laboured by Dr. Frank Mitloehner – a leading global expert on air pollution – during an interview with AgriLand on Ireland’s carbon footprint.

Although agriculture is the single largest contributor to overall emissions in Ireland (accounting for 34% of the total) Dr. Mitloehner, a professor and air quality specialist in the Department of Animal Science at the University of California in the city of Davis in the US, highlights that crucial differences exists between ruminant emissions (methane) and carbon emissions from other sectors (transport, industry, energy, etc).

Later the conversation turns to controversial proposals from environmental and some political quarters that a reduction in the national herd may be necessary to reduce Irish agriculture’s carbon footprint; on this Dr. Mitloehner has “some good news and some bad news”.

Livestock vs. fossil fuels

Firstly, Dr. Mitloehner, who has been at the forefront worldwide when it comes to assessing the environmental impact of agricultural emissions, explains in detail the specific contrast between livestock and fossil fuel emissions.

“Fossil fuel related carbon emissions (greenhouse gases) are so different from livestock related ones.

“The livestock related ones go through a cycle, while the fossil fuel related ones go through a one-way street – from the ground into the atmosphere.

“So the one third of agricultural greenhouse gases in Ireland is very different – not only in quantity, but also in quality – when compared to the two thirds of your carbon which is from fossil fuels.”


Delving deeper into this, Dr. Mitloehner, whose work has informed national and international carbon policy, says the scientific perspective on methane has changed recently.

And so, he explains “the new way” that scientists in the field view methane.

“Methane is a carbon containing compound; methane is CH4. The ‘C’ in the methane is carbon, so where does that ‘C’ come from?”

In order to answer this, the professor highlights the process of photosynthesis [the process by which plants make food].

“What do plans need to grow? They need sunshine, they need water and they need carbon dioxide [CO2].

“That CO2 is in the atmosphere, the plants take that CO2 on and they convert that into carbohydrates such as cellulose.

“In Ireland you have a lot of that; you have cellulose everywhere; you have grassland all over the place.

“Cellulose is by far your most abundant biomass in Ireland, by far. And actually, it is the most abundant biomass in the world.

“The only animals in the world that can take cellulose and make it into human usable foods of the highest quality are ruminants.

“Only ruminant animals can digest cellulose – and not just recycle it, but upcycle it nutritionally into very bio available and highly digestible protein.

“And not just protein; but also these products contain all the other essential macro and micro nutrients such as vitamin B12, iron, iodine and so on.

“So the CO2 that was in the atmosphere is converted into carbohydrates like cellulose in the plants; and sooner or later a cow, or a sheep, will eat that grass and then convert some of that carbon into methane.”

Methane’s 10-year lifespan

What happens next is also quite crucial information for farmers to note.

“That methane is then both belched out ,and comes out in animal manure.

“And then within 10 years – not 1,000 years as is the case with CO2 but within 10 years – that methane is destroyed into the atmosphere.

“Methane is destroyed in the atmosphere by an atmospheric process called ‘oxidation’.

“Then that methane – that is now in the atmosphere – is converted back into atmospheric CO2; and that CO2 is going back into plants, going back into photosynthesis to grow new carbohydrates.

“In other words this so-called ‘biogenic carbon cycle’ – from atmospheric CO2, to plant-derived carbohydrates, to enteric methane produced from cattle and sheep, to atmospheric CO2 again – is a cyclical event.

“It is not new carbon that we have; but it is recycled carbon.

“We are not producing new carbon in this cyclical situation, unless we add additional livestock.”

Herd size

Where livestock numbers are increased, methane also increases, Dr. Mitloehner clearly states.

“The good news is that if you have constant livestock numbers, then you are not adding any new additional carbon to the atmosphere; that means you are not adding any new warming to the atmosphere.

“Constant or decreasing numbers of animals means no additional warming caused by those herds.

“But if you increase animal herds, particularly ruminant herds, then you are putting new carbon into the atmosphere and that is something that is a negative.”

Stored under ground

In closing, Dr. Mitloehner again emphasises how Ireland’s agriculture sector emissions (34%) are different from the remaining two thirds of carbon emissions in the country.

“Most of the carbon from livestock in Ireland goes through the cycle that I just described, so most of that carbon is not new carbon; it is recycled carbon.

“Two thirds of the carbon in Ireland is not recycled and it is related to fossil fuel use – the use of oil, coal and gas.

“That is not recycled at all because that is carbon that was stored in the ground for millions of years.

“We extracted it over the last 60 or 70 years – over half of it is already taken out of the ground – and we are burning it and by burning it we are putting that new carbon into the atmosphere.

“And every time the sun hits it, these carbon molecules heat up and trap the heat and that is the reason why fossil fuel related carbon emissions (greenhouse gases) are so different from livestock related ones.

“The livestock related ones go through a cycle and the fossil fuel related ones go through a one-way street – from the ground into the atmosphere.”

Stay tuned for more from AgriLand‘s interview with Dr. Frank Mitloehner…