Most methane is emitted when cattle burp. Nitrous Oxide (N2O) is emitted from soil when urine, faeces and fertilisers are broken down by microbes in the soil.
How are the different greenhouse gases are compared?
To compare agricultural emissions with other sectors, the methane and nitrous oxide gases are converted into CO2 equivalents as these two gases have a different life span and effect in the atmosphere.
The standard units used for carbon accounting are CO2 equivalents and the standard ratios are based on Global Warming Potential (GWP) over 100 years.
The methane ratio is 25 - i.e. one tonne of methane will cause the same amount of warming as 25 tonnes of CO2. Methane is shorter lived than CO2 (~12 years for methane and 100s of years for CO2) and creates a strong burst of warming, but over a shorter period.
The nitrous oxide ratio is 298 – it is a much longer lived molecule.
The National Inventory
Each year the Government produces a National Inventory Report summarising New Zealand’s annual greenhouse gas emissions, which are categorised into five sectors (agriculture, energy, industrial processes, waste, and land use change and forestry). The inventory covers the emissions of carbon dioxide, methane, nitrous oxide and fluorinated gases, and reports these emissions as units of carbon dioxide equivalent (CO2-e) in order to account for the different global warming potency of these gases.
The information for the agriculture section of the inventory is gathered from a variety of sources including:
- Agricultural Production Survey and Census
- LIC/DairyNZ Dairy Statistics
- Beef & Lamb NZ
- Deer Industry NZ
- Slaughter statistics
- Fertiliser Association
- Assure Quality
- Potatoes NZ
- Balance
- Ministry for the Environment.
Following methodology agreed by the IPCC (Intergovernmental Panel for Climate Change), the Government calculates the emissions for all the major activities on farms, producing tables and graphs in different categories which form part of the National Inventory Report.
The 1990-2015 National Inventory Report and a brief snapshot can be downloaded from Ministry for the Environment’s website.
New Zealand greenhouse gas emissions
New Zealand has a unique GHG profile compared to other developed countries around the world because our agricultural sector is a significant part of our economy. Also, a large proportion of our energy comes from renewable sources. Agricultural emissions make up almost half of New Zealand emissions, while in other developed countries, agriculture makes up around 11 percent on average.
New Zealand’s greenhouse gas inventory for the year 2013. Emissions from forestry are not included in the estimate of total emissions. Percentages may not add up to 100 due to rounding.
Source: Ministry for the Environment, New Zealand’s Climate Change Target (2015).
Dairy industry greenhouse gas emissions
Note: Most of the dairy sector’s emissions come from our dairy farms, mainly from methane and nitrous oxide gases.
Source: Ministry for the Environment, New Zealand’s Climate Change Target (2015).
