VetSalus Briefing: Some basic facts about methane
With the high media profile being generated by COP-26 it is not too surprising to find methane back in the headlines again. What is maybe surprising to anyone looking for a logical science based approach, is the frequency with which the words dairy industry and methane appear in the same sentence. This VetSalus bulletin will reinforce a few basic scientific facts about methane. Over the coming weeks we will also produce some in-depth articles on COP-26 topics.
Here are a few facts about methane and its impact upon climate change:
- Methane is a potent greenhouse gas. Its effects on global warming are estimated to be around 25x more potent when compared to carbon dioxide, using the most commonly applied benchmark GWP 100 CO2e (Global warming potential over 100 years - carbon dioxide equivalent) (1) In contrast, nitrous oxide (N2O) has about 289x global warming impact compared to CO2.
- Methane is short-lived in the atmosphere, lasting only about 12 years compared to the hundreds of years for carbon dioxide (2).
- Methane, because of its relative potency and short term nature, undoubtedly provides an opportunity to impact positively on climate change, in the immediate future.
- Methane can be generated from a number of sources, including (3):
- Biogenic: from the breakdown of complex carbon containing compounds by bacteria and other micro-organisms. This occurs in the ruminant digestive process, indeed to some degree in all digestive processes, as well as part of the natural decomposition of all organic matter e.g. rotting wood
- Pyrogenic: primarily from the burning of wood
- Thermogenic: primarily from the burning of fossil fuels but leaks from oil and gas pipelines and fracking can be included here
- In an environment where photosynthesis is ongoing, and this would include all farms where herbivores eat grass, biogenic and pyrogenic methane is part of a closed cycle involving methane, carbon dioxide and more complex organic compounds. No increase in methane levels results from the progression of this cycle.
- Methane levels have not significantly increased over the last twenty five years (4).
- Agriculture contributes approximately 18% of total greenhouse gas emissions. This includes all sources from agriculture, including arable, forestry, rice cultivation and other land based activities.
- Livestock farming contributes around 6% of total greenhouse gas emissions, but this is not all methane. Carbon dioxide and nitrous oxide, the latter a very potent greenhouse gas, are also generated by agricultural activity.(See graphic below (5)).
- Differing production systems (e.g. pasture based, housed) will make different contributions to atmospheric methane emissions.
- The standard method of measuring the global warming potential of greenhouse gases is by using GWP 100 CO2e. (global warming potential over 100 years carbon dioxide equivalents; methane has a 100 year GWP Co2e of 25. i.e 1 tonne of methane released in the atmosphere has as much global warming potential as 25 tonnes of CO2 (6).
- But methane does not last 100 years in the atmosphere; the average methane molecule lasts 12 years (7). This has led to the development of an alternative methodology for comparing global warming potential , called GWP* (8).
- One recent estimate from the Food and Agricultural organisation of the United Nations assesses the contribution of milk and other dairy products as 2.7% of anthropogenic greenhouse gas emissions (9). This includes nitrous oxide and carbon dioxide contributions.
The above information can be readily checked and referenced online.
At VetSalus we recognise that methane is a potent greenhouse gas and our organisation is committed to leading and enabling vets to contribute to the reduction of all greenhouse gases, particularly when providing professional services in a farming environment. We also firmly encourage the understanding and application of a science based approach. The above facts clearly indicate that the primary focus must remain the reduction of greenhouse gas generation from fossil fuel sources, particularly in major industrial countries.
More information on the subject can be found in the news section of our website.
- Lynch, J., Cain, M., Pierrehumbert, R. & Allen, M. 2020. Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants. Environ. Res. Lett. 15 (2020) 044023