Emission sources

Livestock supply chains are a significant source of global greenhouse gas (GHG) emissions, and emit an estimated 7.1 gigatonnes of carbon dioxide-equivalents per year, representing approximately 14% of all human-induced emissions (Gerber et al. 2013). GHG emissions of the livestock sector are mainly comprised of methane (44%), nitrous oxide (29%) and carbon dioxide (27%). Enteric fermentation, a natural part of the digestive process for many ruminant animals, accounts for 39% of livestock sector emissions. Other significant sources of emissions are feed production and processing (45%) and manure storage (10%). The remaining 6% of GHG emissions is attributable to the processing and transport of livestock products (Gerber et al. 2013).

Soil falling from hand in field  VIDEO: Sources of greenhouse gas emissions on dairy farms
Dairy farms contribute to GHG emissions from a range of sources.

  • National greenhouse gas emissions

    In 2016, Australia’s emissions were estimated to have been 541 million tonnes of carbon dioxide equivalent (Mt CO₂-e) across all sectors (Department of the Environment, National Inventory Report 2017). The energy sector is the main contributor to greenhouse emissions accounting for 53% followed by transport at 18%.

    In 2015 agriculture accounted for 13% of Australia’s greenhouse gas emissions.

  • Dairy industry emissions

    The dairy industry accounts for 12.5% of agricultural emissions, or about 1.6% of total national greenhouse gas emissions. This may not sound significant, but for a typical dairy farm (300 cows doing 6,000 litres) this amounts to more than 2,000 tonnes of carbon dioxide equivalent (CO2e).

    Most dairy farm emissions are from methane (CH4) and nitrous oxide (N2O). Methane from enteric fermentation is the biggest source of emissions from dairy farms (average Australian dairy farm: 57% of emissions; Figure below), followed by methane and nitrous oxide from urine and dung (18%). Nitrogen fertilisers cause emissions (6%) through both their production and application in dairy systems.

    Table: Breakdown of greenhouse gas emissions generated on farm. Source: Adapted from data published by Christie, K.M; Rawnsley, R.P; Phelps, C; Eckard, R.J; 2016, using updated NGGI methodology (Australian Department of Environment and Energy, 2015).

     Enteric CH4
     CH4 from dung and urine
     Direct N2O from dung and urine
     Indirect N2O from dung and urine
     N2O from N fertiliser
    In addition to the greenhouse gas emissions counted as ‘on-farm’, dairy farms also emit significant amounts of carbon dioxide through the on-farm use of fossil fuels and electricity (electricity and fuel; 8.9%), purchased feeds and concentrates (7.9%) and purchased fertilisers (3.1%).

    There is a range of pre- and post-farm gate activities that generate their own greenhouse gas emissions, which contribute to the dairy industry’s total carbon footprint.

    Pre-farm emissions: Many inputs brought onto the farm have an embedded carbon footprint and become part of the total dairy industry carbon footprint despite the fact that in the national emissions accounting scheme, they are not reported as dairy farm emissions. E.g. Embedded emissions from bought-in feed and fertiliser, as well as other ‘pre-farm’ emissions associated with transport, farm chemicals, equipment etc, but these are very minor.

    Post-farm gate emissions: The total amount of greenhouse gas emissions from dairy manufacturing in Australia is around 5% of the total emissions from dairy farms. Most of the dairy manufacturing in Australia occurs in Victoria. E.g. The majority of emissions from dairy manufacturing are carbon dioxide due to energy consumption through electricity and on-site energy use.

    The most important factor in determining a dairy farm’s emissions is simply the amount of milk produced. On this emissions intensity basis (i.e. emissions per tonne of product), dairy farms are relatively low emitters (Figure below).

    Brown et al 2011

    Figure: Average emissions per unit of product for Australian farm types. Source: Brown et al., 2011.

    Although the carbon footprint of Australian dairying is one of the lowest internationally, there is still scope to improve efficiency. The Australian dairy industry has made a commitment to minimising its environmental footprint, including reducing greenhouse gas emissions intensity by 30%.

    There are many ways that greenhouse gas emissions from dairy farms can be reduced, i.e. via management changes to the herd, the feedbase and the soil. See Suggested practices.

  • References

    Browne N, Eckard R, Behrendt R, Kingwell R (2011). A comparative analysis of on-farm greenhouse gas emissions from agricultural enterprises in south eastern Australia. Animal Feed Science and Technology 166-167, p641–652.

    Browne, NA, Behrendt, R, Kingwell, RS, Eckard, RJ (2014). Does producing more product over a lifetime reduce greenhouse gas emissions and increase profitability in dairy and wool enterprises? Animal Production Science, 55(1), 49-55.

    Christie, K., Rawnsley, R., Phelps, C.,Eckard, R. (2016). Revised greenhouse-gas emissions from Australian dairy farms following application of updated methodology Animal Production Science, 58(5), 937-942.

    Department of Agriculture, 2013, Australian agriculture: reducing emissions and adapting to a changing climate - Key findings of the Climate Change Research Program

    Gerber PJ, Steinfeld H, Henderson B, Mottet A, Opio C, Dijkman J, Falcucci A, Tempio G. 2013. Tackling climate change through livestock – A global assessment of emissions and mitigation opportunities. Food and Agriculture Organization of the United Nations (FAO), Rome.

    Whole farm systems analysis research program – publications available via Primary Industries Climate Challenges (PICCC) website.