6.3  Agricultural methane

Enteric emissions from grazing ruminant are responsible for about 87% of New Zealand’s total methane emissions, and 99% of methane emissions from agriculture O’Hara et al. (2003). Most methane emissions are from sheep and beef farming and dairy.

A feasible short-term mitigation option is diet manipulation to decrease emissions. Increasing feed intake decreases the methane emission per unit of intake and increases productivity - methane represents a loss to the animal of about 6% of the gross energy in the feed. However, currently data on abatement potential, costs and viability are lacking.[15]

Current government policy exempts the agricultural sector from price measures provided adequate research is undertaken. Potentially, animal slaughter numbers could be monitored and emissions calculated using national averages. However, implementing a price-based instrument for methane emissions would result in large financial transfers between farmers and the government with possibly a very low level of environmental gain (Kerr and Hendy, 2004). With a permit system, the complicated question of allocating permits would need to be addressed.

6.4  Nitrous oxide emissions

Nitrous oxide emissions make up over a quarter of non-carbon dioxide emissions. Nitrous oxide is primarily related to nitrogen fertiliser application in both farmland and cropland and to animal numbers. As well as reduction in greenhouse gas emissions, proper management of agricultural nitrogen could also lead to a reduction in the nitrate pollution of waterways.

Various animal, grassland and cropland management options are available. These involve more efficient fertiliser application, reduction of nitrogen in feed (although this may lower productivity), and effluent management. There are interactions between nitrate pollution of waterways and nitrous oxide emissions, with the possibility of “win-win” management options.

Observing and monitoring management techniques on a farm-by-farm basis would be very costly. In this case, a blunt instrument such as taxing fertiliser may be preferable to avoid these high costs.

6.5  Other greenhouse gases

The non-carbon-dioxide greenhouse gases that do not arise from agriculture form a very small proportion of New Zealand’s GHG emissions. Most methane and nitrous oxide emissions are from agriculture, though there are minor contributions from waste, energy and industry. The other three GHGs, PFCs, HFCs and SF₆, combined only contribute about 1 percent of New Zealand’s total emissions. Current policy relating to these three gases involves a voluntary policy approach, with agreements negotiated between government and industry. The government has recently launched a discussion paper on ways to reduce synthetic greenhouse gas emissions.[16]

Measurement issues for emissions of these three synthetic gases are very different to those for carbon dioxide. Given the small volume of these emissions and the potentially very large costs of developing and monitoring a system for regulating them, it is unlikely to be efficient to include them in a permit system in the near future. However, strategies aimed at learning about ways to limit these emissions might find a place in policy a great deal sooner.