A lot of people, amongst them Britain’s Lord Stern and Sir Paul McCartney, argue that eating less meat could help save the planet. But there is a growing body of evidence that it is not simply a case of less meat means less heat.

Most of the world’s farmland is grassland. For reasons of rainfall, soil type or topography it can’t be ploughed and it should never be irrigated. The only way to produce food from grasslands is to graze ruminants—animals like cows, sheep and goats—on it. Most mammals, and that includes humans, cannot digest grass. But ruminants possess several compartments in their stomachs. One, the rumen, houses microbes that can digest grass. The problem is that this microbial digestive process also produces the greenhouse gas methane as a by-product.

Methane is a potent, if short-lived greenhouse gas. It is given a global warming potential rating of 25 times that of carbon dioxide, though it has a lifetime of 9 to 12 years in the atmosphere, compared with carbon dioxide which can last more than 100.

Some sectors of the community have leapt on this information, arguing that eating less beef, or not eating it at all, would be better for the environment. But this raises several questions: what happens to the grasslands that are no longer grazed?

What do we eat instead? How will its carbon footprint compare? What about the role livestock traditionally play on farms, eating waste and providing natural fertiliser? And should we be comparing the natural cattle cycle—that actually fixes carbon—with the burning of fossil fuels?

Grasslands account for sixty per cent of the world’s farmland. Can we ethically refuse to produce food from so much land in a world where a hungry population is rapidly increasing?

Ruminants produce protein from plants in areas that are unsuitable for any other agricultural activity. And before there were modern cattle there were wild ruminants: bison or buffalo, caribou, wildebeest, mouflon, auroch and goats. And they all produced methane.

The great bison herds that swarmed across the US prairies before white settlement, along with other native ruminants like elk and deer, are estimated to have produced 86 per cent of the methane of the current US cattle herd.

When modern day ruminants, cattle and sheep, are removed other ruminants usually move in. When the Maasai tribes and their cattle herds were removed from the Serengeti, to create a national park the native ruminants—buffalo, wildebeest, gazelles and giraffe—replaced them. They bred up and created their own methane.

Australia—apart from its population of feral goats and camels—is a special case. Its native herbivores are macropods: kangaroos and wallabies. Macropods also have complex stomaches, but their main byproduct of digestion is succinate. Contrary to widespread belief they do produce methane, albeit less than ruminants fed the same diet. There are only a few studies on macropod emissions. The most recent, on red necked wallabies in the Copenhagen zoo, found they produced between 25 and 33 per cent of the methane of a ruminant, per unit of food ingested.

Another byproduct is a whole new dietary category: kangatarians, people who eat kangaroo but not other red meat, on environmental grounds.

Interestingly, macropods, and this is the polite way of putting it, excrete most of their methane through flatulence, whereas cattle belch out 95 to 98 per cent of theirs.

The macropod research also provides an interesting line of investigation: could their succinate-producing bacteria be introduced into cattle, and cut their methane emissions?

The Australian naturalist George Seddon argued the main herbivores in Australia were insects, especially termites. And guess what termites produce: methane, three per cent of global methane to be exact. Richard Eckard, who is Associate Professor with the Melbourne School of Land and Environment among other titles, thinks it is quite feasible that termites produce more methane, per area in the Northern Territory, than livestock.

Australian beef cattle spend most of their lives on grass, but many spend 50 to 120 days at the end of their life in feedlots, being fed grain. There they are mostly fed low-grade wheat that is unfit for flour milling, crops grown specifically for livestock like sorghum and oats, and the waste products from making canola and cotton seed oil.

Many environmentalists oppose feedlotting due to its intensive nature and the unnaturally high grain diet. But feedlot cattle grow more quickly than grass fed cattle, and that means less greenhouse gas. In fact, Australian grain fed cattle are estimated to produce 38 per cent less greenhouse gas emissions than grass-fed cattle. They grow faster again if they are administered Hormonal Growth Promotants.

Research in the UK has found that organic farms are less energy intensive than conventional farming, but they are also less productive. That means organic livestock have higher greenhouse gas emissions per unit of milk or meat.

But the bottom line is we don’t really know how much methane our cattle are producing, for the simple reason they are animals, not machines. Methane production is influenced by diet, by productivity and by genetics: there can be a 15 per cent difference in methane emissions per animal within the one herd.

Ross Garnaut’s Climate Change Review reported livestock greenhouse gas emissions accounted for about 10 per cent of Australia’s total. Emissions have declined by 13 per cent since 1990, largely because of a fall in sheep numbers from 174 to 74 million. Garnaut pointed out improved animal husbandry over the past 20 years, undertaken for commercial reasons, had also reduced emissions per unit of output. He noted that these developments could go further.

The former Chief of CSIRO Livestock Industries, Alan Bell estimates beef cattle account for up to seven per cent of Australia’s greenhouse gas emissions. And that figure is set to fall. The current estimate is based on old data that have recently been found to overstate the methane produced by northern cattle by 20 to 30 per cent. With about half the nation’s cattle in the north, this means a significant downward revision.

Bell agrees with Garnaut that both beef and dairy cattle have become much more efficient: as production per animal increases, the carbon footprint per kilo of steak or litre of milk decreases. Bell points to work by a student in his former department at Cornell University, Judith Capper. She estimated that in 2007, US dairy cows produced just 37 per cent of their 1944 greenhouse gas emissions per unit of milk, a figure in line with their dramatic increase in milk productivity.

So what would happen if Australians, in the interests of lowering our greenhouse gas emissions, decided to stop producing cattle?

Grasslands have another important role to play: sequestering, or fixing, carbon.

The CSIRO has estimated that 164 million tonnes of greenhouse gases could be stored each year through agricultural activities like rehabilitating grasslands, restoring soil and vegetation carbon, and reducing savannah (northern grassland) burning. Last year Australia emitted an estimated 540 million tonnes of greenhouse gases.

Grasslands fix carbon as they grow; but they have evolved to be eaten. If they were no longer grazed the grasses would grow rank, and stop fixing carbon. And they would in all likelihood burn.

Bushfires, on average, burn over 500,000 square km of Australia annually, mainly in the grasslands in the northern half of the country. Bushfire accounts for about three per cent of the nation’s net greenhouse gas emissions.

If a person decides not to eat meat, what do they turn to for protein, and what environmental impact will that substitute have? This is a question currently being asked in the UK.

There, a study by Cranfield University, commissioned by the environmental group WWF, reported that many meat substitutes are produced from soy, chickpeas and lentils, But these crops can’t be grown in Britain. The report found a switch to these substitutes would result in more foreign land being cultivated, and raise the risk of forests being destroyed to create farmland. It also found meat substitutes tended to be highly processed and involved energy-intensive production methods.

One of the study’s authors, Donal Murphy-Bokern, said: “For some people, tofu and other meat substitutes symbolise environmental friendliness but they are not necessarily the badge of merit people claim.”

While the UK imports its soybeans from cleared Amazon forest, Australia at least grew about 14 per cent of the soybeans it consumed last year. A major limiting factor in Australia is irrigation water: under Australian conditions soybeans need six million litres a hectare, slightly less than cotton’s 6.3 million litres.

Soybeans, lentils and chickpeas also need cleared land, something else that has a finite supply. This is a particular problem in Australia where soil types, restrictions on land clearing and competition with the mining industry all limit supply. They need diesel-guzzling, greenhouse gas producing tractors as well as fertilisers and herbicides—which also involve the production of more greenhouse gases.

And soybeans need to be processed, whether into soy milk or tofu, for consumption, and that processing takes energy, and we know what that means.

Animal products supply a third of all the world’s protein. If we eliminated livestock we would have to produce half as much again vegetable protein crops to replace meat.

But in Australia the shift from pasture to crop land results in a reduction in soil carbon. Increasing soil carbon will be critical to Australia’s future carbon balance. And the most effective way to increase carbon levels in soil used for agriculture is to return crop land to well-managed pasture, preferably native pasture.

In mixed farms—those that run livestock and grow crops—livestock play a critical role in eating farm waste and providing natural fertiliser. Livestock were, of course, a major source of soil fertility before the invention of synthetic fertilisers.

And many who don’t eat beef, do continue to consume dairy products: milk, cheese, yoghurt and ice cream. Which brings us back to cattle.

The thing that bothers me most in this debate is not the demonisation of cattle or the failure to understand that cattle are part of a complex ecological system and if you change one part it will impact elsewhere.

No, the thing that bothers me most is the way cattle emissions have been roped into the climate change debate. The increase in greenhouse gases in our atmosphere is overwhelmingly the result of burning fossil fuels. If that wasn’t happening we would not be having this discussion.

Fossil fuels consist of carbon, sequestered using the energy of the sun, hundreds of millions of years ago. Just four litres of petrol uses what was 90 tonnes of ancient life. In the space of one year, the world is using over 400 years of stored ancient energy and carbon. The carbon dioxide produced will remain in the atmosphere for a century. It is a one way street.

But the carbon released by cattle in methane was sequestered just last week, last month, maybe even last year. And within 9 to 15 years, the carbon in that methane will be sequestered again in a plant, perhaps in grass, to go again through the same cycle. Cattle are part of a natural biological cycle. In it, carbon is sequestered, used, released in a gas and sequestered again. I fail to see how this is the moral equivalent of putting tens of tonnes of fossil life into your petrol tank.

And you could look on cattle as a carbon sink. Get rid of them, and where does the carbon go?

So what is the environmentally conscious consumer to do?

The UK Sustainable Development Commission drew up a list of 13 priorities, as part of its advice to the UK government on a sustainable diet.

Guideline number one was “consume less food and drink”. Britain, like Australia, has a growing obesity problem. Reducing the consumption of meat and dairy products comes in at number eight—after reducing food waste, eating seasonally, not driving to the shops and improving food management at home.

If you walk or cycle to the butcher shop, take home some locally-grown steak and cook it that evening, rare over natural gas, is your carbon footprint smaller than driving to the supermarket, buying a soy-based product that was grown and processed overseas, then having to throw out leftovers because the kids wouldn’t eat it?

One thing is clear: it is not as simple as just giving up red meat.

This piece was originally broadcast on the ABC’s Occam’s Razor program (12 August 2012). Links to external sites have been added for publication on Shaping Tomorrow’s World.