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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Scientists at the European commission have cast doubt on whether biofuels could ever be produced sustainably in significant quantities, dealing a blow to the aviation industry, which sees such fuel as a key way to reduce its emissions.

The researchers argue that the greenhouse gases emitted in making biofuel may well negate most of the carbon dioxide savings made by replacing fossil fuels. Of particular concern is the uncertainty over emissions of the potent greenhouse gas nitrous oxide.

Heinz Ossenbrink, of the EC’s Institute of Energy (IoE), said research carried out by EU-funded scientists increasingly pointed to a long-term problem for large-scale biofuels use, namely the emissions of nitrous oxide. This is about 270 times more potent than carbon dioxide as a greenhouse gas and is released through use of fertilizers to grow biofuel crops. “Some of the older studies don’t take that into account,” he said. “We have now come to less positive values for biofuels.”

The UN’s Intergovernmental Panel on Climate Change does consider the production of nitrous oxide when deciding on the sustainibility of particular biofuels, but errors in its calculations are known to be large. “That’s because there’s such a huge local variation – [emissions] could double from one end of the field to the other and hundreds of times between the fields in the same country and thousands of times around the world,” said Robert Edwards, of the renewable energies unit at the IoE.

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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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Corinna Byrne , co-ordinator of the Carbon Cycles and Sinks Network, examined the policies needed to get Irish land to absorb CO2 rather than release it. Besides discussing how the large amounts of carbon locked up in peatlands can be safeguarded, she reviewed the role that biochar could play in reducing nitrous oxide and methane emissions and building up the fertility and carbon content of the soil.

Corinna Byrne – Carbon Cycles and Sinks from Feasta on Vimeo.

Recorded on day three of The New Emergency Conference: Managing Risk and Building Resilience in a Resource Constrained World. Held on 10-12 June 2009, All Hallows College, Drumcondra, Dublin 9, Ireland

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG),  more powerful GHG.  Applications of organic and mineral on agricultural soil are one of the main anthropogenic sources. These fertilisers also produce nitric oxide (NO) which damages the ozone layer. Previous studies on the effects of applying natural organic and mineral fertilisers on N2O and NO emissions have produced contradictory findings.

Emissions are influenced by conditions such as soil type, crop, temperature and water levels in the soil.

Research, conducted under the EU NitroEurope project, investigated the effect of both types of fertiliser on a non-irrigated crop under Mediterranean conditions. The research observed brief rises of N2O emissions in autumn when the first rainfall events occur and the dry soil becomes wet. An emission factor was calculated which related N2O emissions to the amount of barley produced. This indicated that digested pig slurry is the most efficient fertiliser for this type of Mediterranean agrosystem if the aim is to reduce N2O emissions without reducing crop yield. In comparison, composted residues mixed with sewage sludge and urea both had high emissions factors, i.e. it would not be possible to reduce N2O emissions without also reducing crop yield. 

 Source:

1. Meijide, A., García-Torres, L., Arce, A. et al. (2009). Nitrogen oxide emissions affected by organic fertilization in a non-irrigated Mediterranean barley field. Agriculture, Ecosystems and Environment. 132: 106-115.