Letter: Livestock emissions

From Richard Douthwaite

Bijal Trivedi gave much valuable information on research into potential ways of reducing greenhouse gas emissions from ruminants (20/27 December 2008, p 48). Where he erred, however, was in treating animal emissions as equivalent to those from fossil fuel sources.

True, a molecule of methane belched by a cow has the same warming effect as a molecule of the same gas released by, say, an escape from a natural gas pipeline. But that effect is not the same after the two molecules have oxidised to carbon dioxide and water.

The CO₂ from the cow’s methane had been taken in from the air by the grass the cow ate some days or weeks previously. It is simply returned to the air as part of the natural carbon cycle – whereas CO₂ from natural gas is an addition to the carbon cycle.

Because CO₂ from natural gas adds to the total quantity in the air, it will continue to have a heating effect until global CO₂ emissions fall below the level at which the natural sinks are able to absorb them, and net carbon removal from the atmosphere begins.

From Carol Watson

As a farmer in Australia, I read Bijal Trivedi’s “Kangaroos to the rescue” with great interest. Like so many other critics of the ruminant ecosystem, Trivedi spends a lot of time detailing the extent and means by which ruminants on various diets produce greenhouse gases. But this approach fails to take account of the whole picture.

Ruminants eat grass, and grass uses carbon dioxide to grow via photosynthesis. So it is important to understand the net emissions of the system, rather than be horrified by the gross emissions.

The beauty of ruminants is that they produce clean healthy food and fibre from low-quality and cheap fodder. Our landscape is unsuitable for growing crops for human consumption.

Ruminants are also manageable with low capital input. Farming kangaroos may sound like a great idea to the armchair environmentalist because of their alternative digestive chemistry. But they are notoriously difficult to manage without enormous capital outlay for fencing and handling facilities.

Even if that is done, does anyone know whether they are more or less energy-efficient than ruminants? How easily do they convert kilos of dry-matter into kilos of protein?

Another difficulty, and one which I deal with daily, is whose roos are they anyway? My neighbour breeds them, and at night they feast on my sheep pasture!

Walcha, New South Wales, Australia

Cloona, County Mayo, Ireland