Agriculture releases methane and nitrous oxide. But what are the effects of these greenhouse gases, how are they created, and how do we prevent them?
How much does agriculture contribute to greenhouse gas emissions in Switzerland?
According to the National Greenhouse Gas Inventory, the agricultural sector is responsible for approx. 13 per cent of Switzerland’s greenhouse gas emissions (2020; FOEN 2022). These figures refer to the scope of the agricultural sector as defined by the IPCC for the National Greenhouse Gas Inventories (IPCC 2006). Setting system boundaries differently may lead to slightly different (usually higher) values.
How high is agriculture’s share of methane and nitrous oxide emissions in Switzerland?
According to the National Greenhouse Gas Inventory, agriculture is responsible for 83 per cent of methane gas emissions and 64 per cent of nitrous oxide emissions in Switzerland (FOEN 2022).
To what extent do methane and nitrous oxide contribute to climate change?
According to the National Greenhouse Gas Inventory, one kg methane has a 28 times greater global warming potential than one kg CO₂ (GWP100; IPCC 2021), averaged over a one-hundred-year period. Methane emission occurs chiefly in the dairy and livestock sector, during the digestion of fibrous feed in the rumens of ruminants (cows, cattle, sheep and goats) and the storage of farmyard manure in liquid form. The global warming potential of nitrous oxide is approx. 265 times that of CO₂ (GWP100; IPCC 2021). Nitrous oxide is produced wherever nitrogen is converted within the agricultural system – during the storage of organic fertilisers and farmyard manure in general, and in particular when nitrogenous fertilisers are applied.
How have methane and nitrous oxide emission trends developed in Switzerland?
From 1990 to 2004, methane emissions fell by 8.5 per cent (FOEN 2022). After 2004 methane emissions rose briefly, after which the trend was again reversed. In 2020, methane emissions were around 10 per cent below levels in 1990.
What caused the reductions in Swiss methane and nitrous oxide emissions?
The reductions are primarily due to genetic progress and the intensification of production, i.e. above all, an increase in the energy density of the ration (a better basic ration and higher amounts of concentrates). Consequently, livestock numbers could be reduced whilst production remained constant or even increased slightly. Nowadays, the average cow produces around 46 per cent more milk than thirty years ago (similar figures for the Federal Information Centre for Agriculture in Germany). She thus also emits more methane and excretes more nitrogen, although emissions per litre of milk have fallen by almost one-fifth.
The introduction of the Proof of Ecological Performance in the early 1990s led to a reduction in the amounts of nitrogen used (farmyard manures and commercial fertilisers), and hence to significantly lower nitrous oxide emissions. This resulted in a substantial increase in nitrogen efficiency.
Both milk-production efficiency and nitrogen efficiency are subject to biophysical limits. Although further progress is possible, it will become increasingly difficult to achieve. Accordingly, only minor advances have been made over the last 10 years.
What, besides advances in breeding, can still be done to reduce methane and nitrous oxide emissions?
Although there are few practical measures with a major reduction effect of over 20%, substantial reductions can be achieved combining several small measures (Bretscher et al., 2017). These include, for example:
- Efficient feeding,
- Feed additives,
- Healthy, productive and long-lived cows,
- Herd management,
- Low-emission storage of farmyard manures (covering, biogas plant).
The implementation of many measures on commercial Swiss farms is often a challenge. Organisational constraints, high costs and insufficient knowhow can wholly or partially prevent the theoretically possible reduction targets from being achieved in practice.
Can the optimised feeding of ruminants reduce methane and nitrous oxide emissions?
A feed ration containing plants that are naturally rich in polyphenols and tannins can reduce methane emissions. However, the necessary amounts of such plants are generally far greater than what is realistic under practical conditions.
In addition, ruminants could be fed with flaxseed or other fat-containing feedstuffs, which can curb rumen methane production. However, the fairly large quantities required to achieve a significant reduction in emissions often makes these measures unattractive for economic reasons.
Various feed additives based on essential oils and other plant extracts can also lower methane emissions. To date, however, a persistent, significant reduction in the animal has only been documented in individual cases.
A methane-reducing effect has been documented for red algae (Asparagopsis taxiformis) extracts.
Supplementary feeding of nitrate or other ‘electron sinks’ can curb methane emissions.
Methane emissions can be significantly reduced with synthetic food additives (e.g. 3-NOP).
Administering methane-inhibiting feed additives is a relatively new area, and there is still only very limited experience from practice. There are many unresolved questions in this respect, especially with regard to the long-term effect. A current compilation of applicable reduction potentials can be found in Hegarty et al. (2021).
A balanced protein/energy ratio in the ration can prevent the excretion of excess nitrogen in farmyard manures. This can contribute to higher nitrogen efficiency and lower nitrous oxide emissions.
Are there side effects to the climate-friendly feeding of ruminants?
Methane-reducing feed additives may also attack or inhibit the useful rumen microorganisms that are responsible for a ruminant’s optimal utilisation of their natural feed resources, particularly of fibre in e.g. grass and hay. This can reduce the efficiency of the animal, i.e. due to lower production, no reduction in greenhouse gases released per litre of milk or kg of meat results overall.
Are ruminants harmful to the climate?
That is too sweeping an assertion, since the emissions relevant to global warming are ultimately from fossil sources. Ruminants feeding on their natural forage base do not use such sources. All of the carbon that it absorbs in this manner is ultimately fed back into the system – viewed over sufficiently long periods of time. Hence, gas emissions with a global warming effect from production systems with ruminants are ultimately based on all measures for intensifying production in which fossil carbon is introduced (chemical fertilisers, supplemental feeds, mechanisation, etc.). Consequently, if measures for lowering an animal’s emissions are targeted at the animal itself (composition of the ration, feed supplements, energy density increase, etc.) it thus makes a contribution to limiting global warming – and the more short-term the observation, the higher the contribution, due to the high global warming potential and the more rapid decomposition of methane. Viewed dispassionately, it is a further production goal which can acquire an economic value whilst raising potential ethical issues.
The food-system services provided by ruminants should also be taken into account: they use resources that are meaningfully accessible to them alone (grassland, but by-products as well ), maintain the landscape by preventing scrub encroachment, and so forth. This happens in particular provided that the food system is still relatively in harmony with nature.
What can consumers do to help?
Different foods have very different greenhouse gas footprints (Poore and Nemecek, 2021). Greenhouse gas emissions from the production of animal-based foods, in particular from the meat of ruminants, are generally many times higher than those from plant products.
Hence, there is also scope for action by consumers, who can substantially influence their food footprint via their diet. By eating according to the food pyramid, the average diet-related greenhouse-gas footprint in Switzerland could be reduced by approximately one-half (Zimmermann et al., 2017).
Food-waste reduction would be a further major contribution to climate protection within the context of the food system.
The consumption of seasonal and local products should also be encouraged to avoid long transport routes (including storage and refrigeration) and reduce climate-unfriendly production of foods in other regions of the world.
Bundesinformationszentrum Landwirtschaft, Deutschland:
FOEN 2022: Switzerland’s Greenhouse Gas Inventory 1990–2020: National Inventory Report and reporting tables (CRF).
Submission of April 2022 under the United Nations Framework Convention on Climate Change and under the Kyoto Protocol. Federal Office for the Environment, Bern.
Hegarty, R.S., Passetti, R.A.C., Dittmer, K.M., Wang, Y., Shelton, S., Emmet-Booth, J., Wollenberg, E., McAllister, T., Leahy, S., Beauchemin, K., Gurwick, N.
An evaluation of emerging feed additives to reduce methane emissions from livestock.
2021 Edition 1. A report coordinated by Climate Change, Agriculture and Food Security (CCAFS), New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), Global Research Alliance (GRA).
IPCC 2006: 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change.
Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)
IPCC 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Last modification 27.07.2022