The Government of Australia produces an annual estimate of anthropogenic greenhouse gas emissions (National Greenhouse Gas Inventory, NGGI), including energy (which includes mining related emissions), industrial processes, enteric fermentation from ruminant animals, manure management, rice cultivation, prescribed burning of savannas, field burning of agricultural residues, and landfills and wastewater handling. For 2008, the NGGI reports the release of 5.6 Tg of CH4, or 120 Tg equivalent CO2, equating to 20% of Australia’s total anthropogenic greenhouse gas emissions (Department of Climate Change, 2010). The reported uncertainty on the total inventory (including carbon dioxide and other greenhouse gases) is only 2%, while reported uncertainties associated with individual source categories range from 5% to 50%.
Enteric fermentation from ruminant animals is the largest source of methane in Australia, accounting for 58% of anthropogenic emissions. These emissions are located across the country, with the largest concentration in the more populated regions of New South Wales (NSW), Queensland (QLD), and Victoria (VIC). Energy production, mainly a result of coal mining in NSW and QLD, accounts for 30% of anthropogenic emissions. Landfills and wastewater handling are the next largest source at 12%, and are located near population centers. In the inventories used in this work, methane emissions from Australia are between 9 and 10 Tg/year, of which 5–6 Tg/year are attributed to anthropogenic sources and 4–5 Tg/year are attributed to natural sources.
Methane is produced in wetlands by anaerobic decomposition of organic matter by methanogenic bacteria. The amount of methane produced is highly variable and is most related to temperature and the depth of the water table. Recent work has estimated that wetlands in northern Australia emit on the order of 1 Tg CH4/year and account for 40%–65% of natural emissions, or 10%–20% of all emissions in Australia (Deutscher et al. 2010a). Emissions from oceans surrounding Australia are on the order of 1 Tg CH4 per year (Houweling et al. 1999). Termites produce methane by decomposing organic material via a symbiotic relationship with anaerobic bacteria. Emissions from termites are a significant source of methane in Australia, emitting approximately 1 Tg CH4 per year (Fung et al. 1991). Emissions from termites vary between species, individual mounds within a species, temperature, and moisture (Fraser et al. 1986). Emissions from termites are not well characterized, due to uncertainties in individual termite mound production and location, and issues in scaling up from measurements of individual mounds to the regional and global scales.
Extract 4 Impacts of red meat production on greenhouse gas emissions
The contribution of protein sources to climate change is through their impact on greenhouse gas emissions. The agricultural sector as a whole contributes ~18% of the total greenhouse gas emissions in Australia (Garnaut 2008). Among the protein sources reviewed, the beef cattle and sheep industries contribute 70.1% of the greenhouse gas emissions from agriculture, followed by the dairy industry at 11.6%. The contribution of protein sources to greenhouse gas emissions ranges from the release of carbon into the atmosphere through vegetation clearance, through to methane production by ruminants and management of greenhouse gases such as nitrogen from feedlots. Ruminant animals (cattle, sheep, goats) are the single largest source of Australia’s agricultural greenhouse gas emissions (2861 Gg CO2-e) and alone contribute ~13% of Australia’s total national emissions. In all, 97% of the greenhouse gas emissions are from enteric (digestive-tract) fermentation, with 3% from faeces. Animals such as pigs, chickens and kangaroos have much lower greenhouse gas emissions than ruminant animals (Garnaut 2008).
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