Many ozone-depleting substances (ODS) have been phased out as a result of the Montreal Protocol and are regulated by EU legislation. N₂O is emitted from natural and anthropogenic sources, the latter including as a byproduct of agricultural fertiliser use and from fossil fuel combustion. Its role in ozone depletion has been known for some years and it is similar to CFCs in that it is stable when it is near the earth’s surface but releases ozone-destroying active chemicals when transported into the stratosphere (between 10 and 50km from the surface). However, N₂O is not defined as an ODS under the Montreal Protocol and, although it is a greenhouse gas (GHG) included in the basket of gases under the Kyoto Protocol, its emissions remain unregulated.

The study was the first to calculate the ozone-depleting potential (ODP) of N₂O. Current global emissions of anthropogenic N₂O are approximately 10 million metric tonnes per year, in comparison with annual emissions of one million metric tonnes of CFCs at the peak of their production in the 1980s.

These emissions of N₂O also have a significant impact on the climate. Of all the non-CO₂ GHGs included under the Kyoto Protocol, N₂O emissions have the second most powerful impact on the climate (after methane). Ozone plays a role in breaking down methane so N2O emissions continue to increase, this will lead to increase levels of methane in the atmosphere as there is less ozone around to break it down.

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Researchers from 17 European countries cooperating in the EU-Integrated Project CarboEurope, led by Detlef Schulze, of the Max Planck Institute for Biogeochemistry in Jena, Germany have compiled the first comprehensive greenhouse gas balance of Europe.

A strong carbon sink of -305 Million tonnes of carbon per year exists in European forests and grasslands which could offset 19% of the emission from fossil fuel burning. However this is partly cancelled out by agricultural land and drainage of peat-land  which emits CO_2. The resulting net CO₂ sink of the European continent is 274 Million tonnes of carbon per year – only 15% of the emissions from fossil fuel burning.

However all European ecosystems are managed and as a by-product of land management other powerful greenhouse gases are released – for example nitrous oxide from fertilizers applied to grassland and crops, and methane from ruminants and from peat-lands. These previously neglected emissions of greenhouse gases from land-use cancel out almost the entire carbon sink, leaving the landscape offsetting only some 2% of the CO₂ emissions from households, transport and industry. 

The situation is worse when focusing on the 25 EU states. Here, although forests and grasslands can compensate for 13% of the CO₂ emitted by fossil fuel burning, emission of powerful greenhouse gases from agricultural emissions and peat mining reduces the effectiveness of the land surface sink to 111 Million tonnes of carbon per year, which is only 11% of the CO₂ emitted by fossil fuels. However, since the emissions of methane and nitrous oxide are relatively higher in the European Union the land surface emerges as a greenhouse gas source of 34 Million tonnes of carbon per year. This effectively increases the emissions from fossil fuel burning by another 3%.

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Strangely, before 1999 there was a strong relationship between change in atmospheric methane concentrations and the world ruminant populations. However, since 1999 this strong relation has disappeared. This change in relationship between the atmosphere and ruminant numbers suggests that the role of ruminants in greenhouse gases may be less significant than originally thought, with other sources and sinks playing a larger role in global methane accounting.

A joint FAO/IAEA report on this can be found here.

Researchers from University College Dublin reported that by including 2% fish oil in the diet of cattle, they achieved a reduction in the amount of methane released by the animals.

Dr Lorraine Lillis, one of the researchers, said, “The fish oil affects the methane-producing bacteria in the rumen part of the cow’s gut, leading to reduced emissions. Understanding which microbial species are particularly influenced by changes in diet and relating them to methane production could bring about a more targeted approach to reducing methane emissions in animals.”

More than a third of all methane emissions, around 900 billion tonnes every year, are produced by methanogen bacteria that live in the digestive systems of ruminants such as cattle, sheep and goats. By volume, methane is 20 times more powerful at trapping solar energy than carbon dioxide making it a potent greenhouse gas.

Approximately 50% of Irish agricultural methane emissions result from farm animals; there have been suggestions that, to help combat global warming, a cap be placed on the number of animals in animal production due to their methane production but with a reduction in methane levels through diet this may not be as necessary.

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The “cow fart”  levy (see post further down) was proposed as  the best way to ensure the “polluter pays” principle was followed in dealing with agriculture emissions and was a better alternative to reducing the seven-million-strong national herd.

The revenue could be used to pay for emission reduction efforts in other parts of the economy, or for research on cutting farm emissions.

The European Commission has  issued a press release stating there was no suggestion from the commission of introducing such a tax in Ireland.

“To suggest otherwise is to deliberately mislead the public. Let me repeat, this story is unfounded and untrue,” said Martin Territt, director of the commission’s Irish office.

Minister for Agriculture Brendan Smith finally weighed into the debate, saying: “It is not a proposal that would be considered under any circumstances by this Government.”

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A ‘cow tax’ may have to be introduced by the Irish Government to help it meet new tough targets for reducing greenhouse gas emissions laid out in the EU’s climate change strategy.

Senior officials have told Minister for Environment John Gormley that imposing a levy on all livestock is the best way to avoid having to cut the size of the national herd. Reducing the size of the national herd “could have serious impacts on economic and social life in rural areas”, according to a departmental memo released under the Freedom of Information Act.

The memo details the cost of offsetting methane produced by Irish livestock and the likely revenues produced by a levy. It proposes a levy set at €5 per tonne of CO2 emitted, which generate revenue worth €104 million for the Government. This implies a levy of €13 for each dairy cow, €7 for non diary cow, €1 for sheep, it says.

The levy could be passed on to the consumer in a similar fashion as the plastic bag levy.

However there is strong opposition to any ‘cow tax’ from the IFA, who warn that it would simply lead to carbon leakage caused by the beef and dairy industry relocating to South America.

A spokesman for Mr Gormley said the levy was “not under consideration at present”, however it is understood the Commission on Taxation is considering the sensitive issue.

The government has also been warned that Irish firms may relocate outside Europe to escape the cost of complying with European legislation requiring emissions cuts of 20 per cent by 2020.

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