Methane and Global Warming Potential

Making sense of the science (with a few opinions thrown in for good measure)

The recent 26th UN Climate Change Conference of the Parties, or COP26 for short, has bought climate change back to the front page of the news as the need for countries to accelerate their efforts to keep global warming to 1.5 degrees was driven home.

What has this got to do with cows?

Ruminant agriculture is right in the firing line. You can’t have missed the headlines linking the consumption of red meat or dairy products to global warming:

‘Eat less meat to avoid dangerous global warming, scientists say’ (1)

“'Cows Are the New Coal.' How the Cattle Industry Is Ignoring the Bottom Line When It Comes to Methane Emissions” (2).

To understand where this view is coming from and why it is not entirely fair you need a bit of background.

Greenhouse Gases (GHGs)

GHGs prevent the energy the earth receives from the sun from leaving the atmosphere causing the earth to warm up. This effect is what allows us to survive by warming the planet to an acceptable level. Without it the earth would be -18 degrees C. However, the accumulation of GHGs due to human activity is causing the earth to steadily heat up further, making human existence less and less sustainable.

The earth’s surface temperature has risen by 1.18 degrees celcius since the late 19th century largely because of the activity of man. The majority of the warming occurring in the last 40 years (3).

The most abundant GHGs are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). These gases vary in how much of the sun’s energy they trap and for how long. Methane has been estimated to cause around 18% of global warming (16). 70% of the methane produced is from anthropogenic sources, 1/3 of this is due to enteric fermentation and release animal waste (15).

To enable the effects of these gases to be compared easily a measure called Global Warming Potential (GWP) was developed, comparing the warming potential of a tonne of each gas to a tonne of CO2.For the comparison CO2 is given a nominal value of 1.The potential warming effect of these gases over a 100-year period, or GWP100, was the metric used in the Kyoto protocol of 1997 which mandated that industrialized nations cut their emissions.

GWP100 assigns CH4 a figure of 28 and N2O, 265.

This is effectively saying that a tonne of methane released into the atmosphere, will warm the earth 28 times more than a tonne of CO2.

GWP has remained the chosen metric in international climate change policy until the present day, 24 years later.

There have been ongoing disagreements about the appropriateness of using a single metric, especially when applied to ruminant agriculture. The Intergovernmental Panel on Climate Change (IPCC) report of 1990 stated that ‘it must be stressed that there is no universally accepted methodology for combining all the relevant factors into a single global warming potential for greenhouse gas emissions. In fact, there may be no single approach which will represent all the needs of policy’ (4).

Part of the issue with adopting a universal metric which tries to directly compare all the GHGs is the different lengths of time they remain unchanged in the atmosphere. Some, such as methane, are short-lived climate pollutants (SLCP) lasting around 10-12 years and others, such as CO2 and N2O are long lived (LLCP), lasting hundreds or even thousands of years. So, although methane is highly potent in the short term, it will be broken down releasing CO2 and water after approximately 10 years.

Cows and Methane

Ruminants have the incredible ability of turning fibre from plants, indigestible to man, into high quality protein. Unfortunately one of the side-effects of this is the production of methane. This is formed by some of the microbes which populate the rumen (and to a far lesser extent the lower GI tract) known as methanogens, Methane is released from the animal mainly through burping and to a lesser extent through farting. The production of methane by methanogens helps the other bugs in the rumen which break down carbohydrates in grass and other feeds, to function optimally. They do this by removing hydrogen from the rumen environment and turning it into methane. The production of methane, as well as being directly damaging to the environment, also represents inefficiency of digestion as a loss of gross energy from the diet of between 6 to 10%. If this energy could be used by the animal to produce meat or milk there would be a double reduction in emission intensity by reducing methane release and by increasing the feed efficiency, reducing carbon inputs.

The amount of methane produced varies depending on what a ruminant eats. Factors such as dry matter intake, neutral detergent fibre (NDF), acid detergent fibre (ADF), forage proportion and lignin content of the diet all help to predict how much methane the cow will produce (5).

Biogenic Carbon Cycle

Methane produced by cows is termed biogenic methane. This forms part of the biogenic carbon cycle: Carbon is captured from CO2 in the air by plants through the process of photosynthesis. This is stored in the plant as carbohydrates. When the plant is eaten, these carbohydrates are broken down in the rumen and methane is released into the air. This methane is converted back into carbon dioxide in the atmosphere, a process taking 10-12 years. CO2 is then captured by plants forming a balanced cycle of release and removal of carbon from the atmosphere. Methane from fossil fuel, on the other hand, is carbon that has been stored for millions of years in the ground, effectively taking it out of circulation. It is released into the atmosphere during the extraction, handling and burning of fossil fuels. Unfortunately, once converted into CO2 in the atmosphere, it doesn’t form part of a balanced cycle, the mass rate of release far outweighing how fast the carbon is fixed back into organic matter. If we can bring about change to reduce biogenic methane production so that ‘the emission rate falls below the sink rate, atmospheric concentration [of CO2] … will fall which means the warming will be reduced from the current level’ (6). It has been estimated that a reduction in global methane emissions by about 4% per year would lead to stabilisation of methane levels in the atmosphere (7) causing no further increase in global warming. Compare this to the release of CO2 into the atmosphere from eg. transport. If the level of emissions is reduced but not stopped altogether, it will still exert an additional warming effect for hundreds of years into the future.

I believe that the way cows are demonised by the media in relation to global warming is a little misleading. Biogenic methane does play a role in climate change and if it continues to rise it will cause significant warming over the short term. However, modest reductions in total methane production would lead to a net reduction of methane in the atmosphere which could even have a net cooling effect on the planet. This is not a get out of jail free card for ruminant agriculture. A growing world population is driving an increasing requirement for high quality protein. A large portion of this will come from animal products. It is imperative that this increased output can be achieved at the same time as implementing strategies to reduce the intensity of emissions for animal products so that there is no net increase in emissions.

Other GHG Sources

It should also be remembered that it is not just about methane. CO2 and N2O are released directly and indirectly in livestock production systems. This occurs through, for example, the use of fertilisers and the breakdown of dung, in the case of N2O, or fossil fuel use in tractors and transport.

The emissions from a typical Australian, pasture based dairy farm come from enteric methane (55%), methane from waaste manure (10%), N2O from manure (10%), N2O from fertilisers (5%), CO2 from energy consumption (10%) and from pre-farm emissions generated in the production of grain and fertiliser (10%) (8).

Industry Response

Meat and Livestock Australia (MLA) has set the target for the red meat and livestock industry to reach net zero greenhouse gas emissions by 2030. The Australian dairy industry has agreed to a 30% reduction in emissions intensity by 2030. Net zero GHG emissions means that, using CO2 equivalents, the sum of emissions minus storage and sequestration of GHGs will equal zero regardless of the level of production of red meat. So, if you want to run more beef units then the goalposts will still be the same, there is no increased allowance for increased production. This would become harder as options to sequester carbon on farm may become become exhausted.

A reduction in emission intensity, in the dairy context, is a reduction in the net amount of emissions per kg of fat and protein corrected milk (FPCM). So, if the industry increases total milk output, then so long as the net carbon (production minus sequestration) for each kg of milk produced reaches the target then the net GHG emissions of the industry as a whole could potentially increase.

As with the MLA pledge, the target will become harder to meet with increased production as carbon storage opportunities on farm become less available and chances to further reduce emissions at an animal level, through increased efficiency or for example, the use of methane reducing feed supplements are exhausted.

It should also be noted that if carbon credits have been sold for carbon stored in the soil then this shouldn't also be counted again against the emissions intensity of milk or beef. Sold credits could therefore limit future opportunities to increase production or even to meet existing targets at the farm's current level of production, without falling foul of contracts.

Global Context

In 2010, estimates were made of the emission intensity per kg of FPCM at farm gate for the different regions of the world. The figures ranged from from 1.3 to 7.5 kg CO2-eq. [±26 percent] with the average global emissions from milk production, processing and transport estimated to be 2.4 CO2-eq. per kg of FPCM at farm gate (9). The 2015 figure for milk produced in Australia was 1.03Kg CO2 eqv. (10) which compares very favourably to the rest of the world, falling under 50% of the 2010 world average. The average global emission intensity per kg beef (carcase weight) has been calculated as 46.2 kg CO2 eqv. taking into account land use change but not soil carbon sinks. When split into regions, the per kg figure ranges from 14 kg CO2 eqv. in Eastern Europe right up to to 76 kg CO2 eqv. in South Asia. The figure for Oceania comes in around 25 kg CO2 eqv. (12). It should be noted that beef produced from dairy animals has been calculated to have almost 4 times lower emissions than that produced from specialist beef herds due to the sharing of emissions with milk production. There is no comparable average figure available for Australia however an extrapolation of a data set from farms in eastern Australia gives a figure similar to the 25 kg CO2 eqv./kg for Oceania as a whole (13). This puts Australia at the better end of the scale. Effective use of carbon storage in the soil could reduce this figure considerably. With the right conditions rates can range from 0.05 to 0.8t C/ha/year though typically don’t usually exceed 0.3t C/ha/year in Australian grazing systems (14).

Summary

The long-term sustainability of ruminant agriculture is the most pressing issue for the industry. Climate change is just one aspect of sustainability but getting it wrong offers the greatest threat not only to farmers but to the population of the planet as a whole. If it is not something you personally consider important then you can be assured that it is of importance to your customers. The production of low carbon food offers a huge opportunity for Australia. The world will need more and more high-quality protein to feed it’s growing population. This will need to come from low carbon sources if global temperature rise is to be kept in check. I strongly believe that livestock farmers will be big part of the solution to climate change and food security.

Sourcing meat from a country a long way away seems counterintuitive when it comes to environmental impact, yet only <5% of the total GHG emissions of lamb and beef supplied from Australia comes from international transportation (13). There are many reasons to buy local, such as supporting the local economy, but when it comes to the global problem of GHGs, the emphasis should be on buying the product with the lowest total warming potential, wherever it is from.

Management of grazing land to maximise its carbon storage potential as well as a reduction in methane emissions, to form an equilibrium with degradation in the atmosphere, will help to curb global temperature rise. Reducing methane output further could even have

a cooling effect on the planet. I would like to see the fossil fuel industry achieve that!

If Australian farmers can produce low carbon food where others can’t AND back it up with the right credentials, they will be able to capitalise on this market and acheive a premium to boot.

References

1. Harvey. F. (2016, Mar 22). Eat less meat to avoid dangerous global warming, scientists say. The Guardian 2. Baker.A.(2021, December 2). ‘Cows Are The New Coal.’ How the Cattle Industry Is Ignoring the Bottom Line When It Comes to Methane Emissions. Time 3. Shaftel, H., Jackson, R., Callery, S., & Bailey, D. (2018). Global climate change: Vital signs of the planet. NASA’s Jet Propuls. Lab. Calif. Inst. Technol. https://climate. nasa. gov/causes/. Accessed, 2022. 4. Change, I. P. O. C. (1990). Climate change: The IPCC scientific assessment. Mass, Cambridge. 5. J.L. Ellis, E. Kebreab, N.E. Odongo, B.W. McBride, E.K. Okine, J. France, Prediction of Methane Production from Dairy and Beef Cattle, Journal of Dairy Science, Volume 90, Issue 7, 2007, Pages 3456-3466. 6. Cady, R. (2020). A Literature Review of GWP*: A Proposed Method for Estimating Global Warming Potential (GWP*) of Short-Lived Climate Pollutants Like Methane. 7. Jardine, C. N., Boardman, B., Osman, A., Vowles, J., & Palmer, J. (2004). Methane uk. The environmental change institute. 8. Dairy Australia (2015) Greenhouse Gases on Dairy Farms: Where do emissions come from? 9. FAO. Animal Production and Health Division Greenhouse Gas Emissions from the Dairy Sector: A Life Cycle Assessment 10. Dairy Australia (2020) Climate Change Strategy: 2020-2025 11. Poore, J., & Nemecek, T. (2019). Reducing food's environmental impacts through producers and consumers (vol 363, eaaw9908, 2019). Science, 363(6430), 939-939. 12. Opio, C., Gerber, P., Mottet, A., Falcucci, A., Tempio, G., MacLeod, M., ... & Steinfeld, H. (2013). Greenhouse gas emissions from ruminant supply chains–A global life cycle assessment. Food and agriculture organization of the United Nations. 13. Wiedemann, S., McGahan, E., Murphy, C., Yan, M. J., Henry, B., Thoma, G., & Ledgard, S. (2015). Environmental impacts and resource use of Australian beef and lamb exported to the USA determined using life cycle assessment. Journal of Cleaner Production, 94, 67-75. 14. MLA (2021) V.SCS.0016: Carbon accounting technical manual carbon-accounting-technical-manual.pdf (mla.com.au)

15. Moss, Angela R., Jean-Pierre Jouany, and John Newbold. "Methane production by ruminants: its contribution to global warming." Annales de zootechnie. Vol. 49. No. 3. EDP Sciences, 2000.

16. Badr, O., Probert, S. D., & O'callaghan, P. W. (1991). Atmospheric methane: Its contribution to global warming. Applied energy, 40(4), 273-313.