First broadcast on 28 April 2021
In this episode, Tom Heap meets the researchers with a host of ideas on how to reduce methane emissions from cattle farms.
Cattle emit huge quantities of planet-warming methane. But they can be stopped! Tom Heap meets Eileen Wall from SRUC, Scotland's Rural College who introduces him to a host of cunning carbon-cutting ideas - from seaweed in the feed and gas masks for cows to barns that can convert methane into energy to power the farm.
Tom is joined by Tamsin Edwards of King's College, London to calculate just how much difference these ideas might make to our warming Earth. Are those the best answers or should we all be persuaded to cut our meat consumption?
Listen now on BBC Radio 4
We asked Society Fellows Dr Michelle Cain from Cranfield University and Professor Vincent Gauci from the University of Birmingham to offer some observations on the potential of certain measures to remove methane from the cattle-farming food chain in reducing carbon emissions. Their points take some of the themes of the programme a step further.
If you can reduce methane emissions from cows by approximately 0.3% per year every year, then the impact of their methane emissions will remain stable, i.e. your methane (CH4) emissions are causing a stable contribution to temperature, and not driving temperatures up. If you decrease your cows’ methane emissions by more than 0.3% per year, then you will be reducing the level of warming that the cattle’s methane contributes, i.e. driving temperatures down. The 0.3% is based on climate modelling by Cain et al. (2019). The cows’ nitrous oxide (N2O) emissions would still be accumulating, and driving temperatures up. You could design a scenario where methane reductions ‘offset’ N2O emissions, so you have a stable contribution to temperature from the cattle emissions. Or, you could undo some past warming if the methane emissions reductions more than offset the N2O emissions.
I personally see methane emissions as having a slice of the radiative forcing pie. Reducing this slice over time will be beneficial. Then you have the questions of how big a slice do we want methane to take up and what sources do we allow to contribute to this?
For cattle, this would have to be considered alongside N2O emissions, as well as land use. Land use arguments for climate friendly cattle are worth attention given deforestation and competition for land (which is a finite resource and can be used for fighting climate change in other ways).
Cows in the pasture (Image: PhilippT/Pixabay)
The table below outlines the current impact on ruminant emissions (mainly cattle) in carbon dioxide (CO2) equivalents.
Methane GWP (AR5) (methane global warming potential – fifth assessment report)
Tg CH4 (teragrams methane)
GT CH4 (gigatonnes methane)
GT CO2 (equiv) (gigatonnes carbon dioxide equivalent)
80% reduction in CH4 emission cited through supplementation with red seaweed
Roque, B., Venegas, M., Kinley, R., Nys, R., Duarte, T.L., Yang, X. and Kebreab, E. (2021), Red Seaweed (Asparagopsis taxiformis) supplementation reduces enteric methane by over 80 percent in beef steers. Plos One, 16(3)
Saunois, M. et al. (2020), The Global Methane Budget 2000 – 2017. Earth System Science Data, 12(3), pp. 1561 - 1623
Red seaweed has only in March of this year been shown to reduce methane emissions by 80%. This could therefore be considered an upper limit on emissions reductions since it is the largest I have come across, but it would suggest a reduction in CO2 equivalents of ~2.5 gigatonnes CO2 per year.
Ruminant emissions offer a big win. In many ways they are a cultural/societal issue. Currently it is acceptable to eat meat and milk but if it became unacceptable, for whatever reason, emissions could be near eliminated. For example, there could be a revolution in the next generation if beef protein can be grown in the laboratory. With an alternative available that tastes near identical, the ethical calculations individuals make may make slaughtered beef unacceptable. Lab grown meat will likely have its own footprint but as an industrial process this could be minimised through design.
Care should also be taken to focus interventions on cattle that are farmed on an industrial scale rather than on extensive farming on sparse grasslands in developing arid countries where the contributions to methane emissions are far smaller. In general, my understanding is that milk herds produce most methane.
There has been an effort to reduce CH4 emissions from a cow production point of view since this is seen as an inefficient use of cow metabolism - redirecting cow ruminant metabolism away from CH4 may make the cows more productive (chiefly for milk).
Cain, M., Lynch, J., Allen, M. R., Fuglestvedt, J. S., Frame, D. J., & Macey, A. H. (2019). Improved calculation of warming-equivalent emissions for short-lived climate pollutants, npj Climate and Atmospheric Science, 2(1), 29
Carrington, D. (2020), No-kill, lab-grown meat to go on sale for first time, The Guardian
Haas, Y., Wall, E., Garnsworthy, P.C., Kuhla, B., Negussie, E., Lassen, J. (2018), Where have we come with breeding for methane emissions – update from international collaborations, Proceedings of the World Congress on Genetics Applied to Livestock Production
39 ways to save the planet is a new radio series by BBC Radio 4 developed in partnership with the Society and broadcast in 2021. It showcases 39 ideas to relieve the stress that climate change is placing on the Earth. In each 15 minute episode Tom Heap and Dr Tamsin Edwards meet the people behind a fresh and fascinating idea to cut the carbon.
Over the course of 2021, the Society will be producing events and digital content to accompany the series.
Featured card image: Peter Ellis and The Nature Conservancy
Featured banner image: Killileikko/Pixabay
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