Change to cow diet cuts methane emissions
With the dairy, beef and sheep industries responsible for 11 per cent of Australia's greenhouse gas emissions, scientists are striving to reduce greenhouse gas emissions from agriculture and may have found the answer.
PT1M33S 620 349It sounds so easy: stop eating red meat to lower greenhouse gas emissions. But nature is far more complicated than that.
There are three critical questions you need to ask before cutting beef and lamb out of your diet for environmental reasons: what will happen to the grasslands that cattle and sheep graze; how will alternate protein be produced; and what will the greenhouse consequences of that production be?
If you decide not to eat meat, where are you going to get your protein? Photo: Getty
About 60 per cent of the world's agricultural land is grasslands, land that is too poor and too dry to be cropped. In Australia, about 70 per cent of the country is grassland. The only way food can be produced from grasslands is by grazing ruminants. Mammals cannot digest grass, but ruminants have special stomachs filled with grass-digesting bacteria. The problem is those bacteria produce methane, which the ruminant burps out.
Methane is a potent greenhouse gas with a rating 25 times that of carbon dioxide over 100 years, although it has a lifetime of 9 to 12 years in the atmosphere.
The experience worldwide is that if cattle are removed from grasslands, the original ruminants re-establish themselves, or ferals invade.
In Australia the main ferals are goats, as well as camels in drier regions. Contrary to popular belief, kangaroos do produce methane, although the actual quantities, and their alternate pathways for digesting cellulose from grass, are the subject of ongoing research. Even termites produce methane: they are responsible for about three per cent of Australia's greenhouse gas emissions.
What if everyone did go vegetarian and the grasslands were not grazed at all? In Australia, they would most likely burn. Bushfire accounts for about 3 per cent of Australia's net greenhouse gas emissions.
The argument overseas focuses largely on the huge quantities of grain, that could otherwise be consumed by humans, that are fed to livestock. This is a practice that is indefensible on environmental grounds. In Australia, most cattle and all sheep are grassfed. Dairy cattle are usually given supplementary feed, which is mostly forage or hay with some grain.
If you decide not to eat meat, where are you going to get your protein, and what are the greenhouse gas consequences? Soy beans, chickpeas, lentils - all the high-protein legumes - are crops that are grown on cleared land, land that is ploughed, fertilised, planted, irrigated and harvested by greenhouse-gas producing machines.
Australia is at its limit of land that can be cleared for cropping, and is in the process of reducing irrigation in its food bowl, the Murray-Darling basin. And talking of irrigation, under Australian conditions soybeans need almost as much water as cotton. Australia produces roughly 15 per cent of the soybeans that it consumes, although much of that is used in stock feed.
Pigs and chickens are monogastric and as a result produce a small fraction, per kilo, of the methane produced by ruminants. Unlike cattle they cannot live on grass. In traditional farm situations they were fed on crop residues and waste, but now significant quantities of grains are grown to feed them.
Meat protein substitutes, ranging from tofu to synthetic meat, are all highly processed and that means more greenhouse gas production.
Estimating methane production is a tricky business. There are a number of figures for the percentage of greenhouse gas emissions agriculture is responsible for, and they are getting better. On Monday, the CSIRO announced methane emissions from Australian cattle were actually 24 per cent lower than previously thought.
Critics of meat consumption like to compare ruminant-produced methane with transport emissions. But fossil fuels are releasing carbon that was sequestered hundreds of millions of years ago that will never be replaced. The methane burped by a cow comes from carbon sequestered in the grass during the last growing season. If that grass keeps growing, or produces seedlings, carbon will be sequestered again next season.
There is no comparison: burning fossil fuels is a one-way street. The methane produced by ruminants is a natural part of an ancient life cycle.
Asa Wahlquist is a rural journalist.
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