How Australia accounts for agricultural greenhouse gas emissions

As a party to the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol and the Paris Agreement, Australia annually reports on its greenhouse gas emissions. The methodology used to estimate Australia's national greenhouse gas emissions is documented in the National Inventory Reports (https://www.industry.gov.au/policies-and-initiatives/australias-climate-change-strategies/tracking-and-reporting-greenhouse-gas-emissions).

Western Australia’s emissions from agriculture totalled 9373 Giga grams of carbon dioxide equivalent (CO₂-eGg) in 2018, or 10.3% of the State’s emissions.

Agriculture is an important source of greenhouse gas emissions

Agriculture was responsible for about 13.5% of Australia’s greenhouse gas emissions in 2018, and the sources (see Table 1) were:

• 68.4% from enteric fermentation in ruminant livestock (eructation and flatulence)
• 17.6% from agricultural soils
• 9.7% from manure management
• 3.5% from liming and urea application
• and the remainder from rice cultivation and field burning of agricultural residues.

Livestock and the manure they create were the dominant source of methane, accounting for 46% of total national methane emissions, and agricultural soils were the dominant source of nitrous oxide, accounting for 57% of total national nitrous oxide emissions.

Not all greenhouse gases are equal

The global warming potential of methane is 28 times that of carbon dioxide, and nitrous oxide is 265 times that of carbon dioxide. This means that 1 tonne of methane is equivalent to 28 tonnes of carbon dioxide; 1 tonne of nitrous oxide is equivalent to 265 tonnes of carbon dioxide.

Each greenhouse gas has a unique residence time in the atmosphere and unique heat-trapping potential. The concept of global warming potential is used to express these unique values relative to carbon dioxide over a specified period. Under the United Nations Framework Convention on Climate Change, the global warming potential of greenhouse gases is expressed in terms of how much carbon dioxide would be required to produce a similar warming effect over 100 years. This is termed the carbon dioxide equivalent value (CO₂-e).

Some emissions are not counted as agricultural emissions

Under current accounting rules, emissions generated during the manufacture and transport of agricultural inputs – such as fertilisers, herbicides, pesticides and agricultural machinery – are not counted as agricultural emissions. Emissions from the fuel used by agricultural vehicles either on-farm or in transporting produce and the fuel used to generate electricity consumed on farm is excluded. Agricultural emissions associated with land clearing and prescribed burning (savannah burning) are also excluded.

Table 1 Greenhouse gas emissions from Australian agriculture in 2018, expressed as Giga grams of carbon dioxide equivalent (CO2-eGg). Emissions from Savanna Burning are reported under Land Use and Land Use Change and Forestry (LULUCF).