The methane menace and hamburgers

A paper on the contribution to climate change of livestock methane emissions has found that the problem is likely to get worse as global demand for meat and dairy products increases. Dr Andy Thorpe, an economist at Portsmouth University, found that a single herd of 200 cows can produce annual emissions of methane roughly equivalent in energy terms to driving a family car 180,000 km.

Whereas carbon dioxide emissions have increased 31 per cent over the past 250 years, methane, which has a higher warming potential and a longer atmosphere lifetime than carbon dioxide has increased by 149 per cent over that time. Dr Thorpe commented that 'Methane emission growth ... has been increasing exponentially in the developing world due to a rise in incomes leading to an increased demand for meat and the "hamburger connection" where developing countries make a lucrative profit supplying meat to developed countries.'

Attempts to curb animal methane emissions have included feeding grazing animals on cottonseed and alfalfa, using food additives, and vacinnating animals with drugs, but it is not clear if they will work on a large scale. A reduction in the amount of livestock kept for meat and milk would only put pressure on other food sources, such as cereals.

Animal methane emissions from developing countries have increased to 75 per cent of the global total, with India and Brazil in the lead. It is thought that atmospheric methane is responsible for one-fifth of the global warming since 1750.

Cows, sheep, goats and camels have an additional stomach and produce large amounts of methane as they digest their food. A dairy cow in New Zealand will typically produce around 80kg of methane a year, just through burping.

The policy pressures this produces is shown by complaints from the Irish Dairy Industries Association that the Republic's commitment to reduce greenhouse gas emissions is piling further economic pressure on the country's beleaguered dairy industry. It was argued that because Ireland's greenhouse gas emissions (GHG)were closely linked to methane from cattle, a 20 per cent cut in GHG emissions would result in a 20 per cent cut in Ireland's dairy herd.

The association complained that there is no international standard for measurement of emissions from enetric fermentation in cattle. The background to these concerns is a sharp drop in prices from 40 cents a litre in 2007 to around 24 now.

Vegetarians would no doubt argue that the GHG emissions of cattle reinforce the case for not eating meat. In practice, it is difficult to see how the problem can be tackled given that the livestock sector is under heavy economic pressure.