How can Australian agriculture achieve net zero emissions by 2030?
By Dr Rachelle Meyer, Postdoctoral Fellow (Farm Systems Analysis)
The land sector is key to Australia meeting its Paris Agreement commitments. Agriculture contributed nearly 14 per cent of Australia’s 2017 emissions – 73 megatonnes of carbon dioxide emissions.
Another 26 megatonnes were from deforestation (mostly due to land clearing for agriculture). Together this is nearly 20 per cent of 2017 emissions, similar to that of Australia’s transport sector.
A variety of pathways have been proposed to restrict warming to 2 °C, but almost all include some element of negative emissions, or carbon sinks, from the land sector. ‘Negative emissions’ is a term used to describe a net reduction of atmospheric carbon – methods that pull carbon out of the air.
What is unclear is just how realistic it is to expect carbon sinks provided by agricultural land to offset much of the sector’s emissions in just 10 years, as proposed by some agricultural organisations. And, if it is possible, what actions are needed to achieve this goal?
Researchers at the University of Melbourne and Energy Transition Hub have addressed these questions with a review of agricultural emissions and the potential of mitigation and sequestration options.
The primary agricultural greenhouse gases are methane and nitrous oxide. These gases have much stronger heat-trapping properties than carbon dioxide, but they do not persist in the atmosphere as long. Their lifespans are more comparable to carbon stored in land sinks, such as trees and soil. In contrast, a portion of carbon dioxide emissions remains in the atmosphere for centuries.
For this reason, as well as logistics, it makes sense to use land sinks to offset methane and nitrous oxide emissions, rather than using land sinks to offset carbon dioxide from fossil fuels.
What can we do today?
The clear first step in reducing agriculture-related emissions is to reduce deforestation. Current projections suggest deforestation emissions are likely to stabilise near current amounts. To achieve the most out of afforestation and reforestation efforts, and offset emissions from sources that are more technically challenging to mitigate, further reductions in deforestation are necessary.
Grazing land use is another area where emissions could be reduced with improved management. Planting perennial pasture and nitrogen-fixing species, ensuring a sustainable stocking rate and improving fire management would reduce grazing land emissions.
Increasing the use of renewables on-farm, particularly in high-input and energy intensive systems, reduces emissions while benefiting farmers. For example, use of anaerobic digestion to convert piggery waste to biogas for energy can reduce on farm emissions by up to 80 per cent.
Similarly, options that improve emissions per unit product are attractive to farmers since they can increase profits. This allows for increases in demand to be met with lower increases in emissions than would otherwise occur. However, these options on their own rarely result in total emissions reductions.
No easy solutions for major emissions sources
These options do not directly address two of the major sources of agricultural emissions — enteric methane from ruminant livestock and nitrous oxide emissions from soils — and are therefore unlikely to reduce agricultural emissions to the extent necessary for net-zero.
Unfortunately, there’s not consistently effective technology for reducing either enteric methane or nitrous oxide emissions.
Enteric methane is generated during digestion in ruminant livestock. It comprises over 70 per cent of Australia’s agricultural emissions and most of this is from low stocking density systems where graziers currently have limited options for substantially reducing emissions.
Nitrous oxide is emitted from soils and increases with fertiliser application, as well as urine and manure from livestock. There are options to reduce these emissions, such as chemical inhibitors, and planting legumes and other plants that capture nitrogen from the environment, reducing the need for fertilisers.
The effectiveness of inhibitors is highly variable and the reasons behind this variability are not well understood. Including legumes in rotations can reduce fertiliser application, but may lead to indirect emissions.
Farmers need a clearer view of the benefits
Mitigation and sequestration options need to be assessed against several criteria. Options that reduce emissions of one greenhouse gas can increase another, requiring calculation of the net impact on whole-farm emissions.
The carbon sink from reforestation and trees on farms serves as a stopgap measure to address net emissions while technological advances are developed for methane and nitrous oxide, but the potential sink is uncertain. Environmental plantings on 12 to 24 per cent of intensive agricultural land are estimated to provide an average annual sink equivalent to 17.5 megatonnes of carbon dioxide emissions to 2060 at $153 per tonne of carbon in 2050. However, the amount of sequestration that can occur in productive farm systems in uncertain. Planting trees on farms may become a more attractive option if the production benefits and potential trade-offs were clear.
Bioenergy is an option that could provide emissions reductions, as well as job opportunities and new income streams in regional areas, but much more research is needed to determine how to sustainably produce bioenergy feedstocks in Australia. More specifically, what feedstocks give the best emissions reductions with minimal impact on food production, biodiversity, and other considerations? There are also several associated governance issues.
For the sector to achieve net-zero emissions, strong and swift action is required. This needs to include substantial investment to address research gaps, encourage producers to adopt options that are not currently commercially viable and promote widespread practice of those that are.
The review, Achieving net negative emissions in a productive agricultural sector, is available now.
Dr Rachelle Meyer is working on the impacts of extreme events and associated risk management strategies for the dairy and red meat industries, as well research to improve nitrogen use efficiency in dairies.