Animals kept for food and labour contribute to a significant proportion of man-made emissions of the greenhouse gas methane. While most developed countries have signed up to the Kyoto Protocol and have targets to cut their greenhouse-gas emissions (including methane), developing nations haven’t. What's more, the proportion of animal methane emissions coming from developing countries has increased to 75%, with India and Brazil in the lead.

Each year, around 600 Teragrammes of methane is produced worldwide, from sources such as wetlands, hydrates, landfill, rice agriculture and biomass burning. It's thought that atmospheric methane is responsible for one-fifth of the global radiative forcing since 1750. And between 55 and 70% of the gas comes from man-made sources.

"Methane emission growth – like carbon dioxide growth – has been increasing exponentially within the developing world due to rising incomes [causing] increased demand for meat proteins and the hamburger connection – developed countries sourcing meat from developing markets," Andy Thorpe of the University of Portsmouth, UK, told environmentalresearchweb. "Attempts to curb enteric [intestinal] emissions are, to date, largely in the early stages – and so the swiftest way to reduce methane enteric emissions is via herd down-sizing."

But cutting the number of animals presents its own problems; Thorpe believes there is no easy answer. "If we reduce draught animal inventory – water buffalo, oxen etc. – this is likely to lead to increased carbon dioxide emissions as petrol power sources are used," he explained. Animals for meat are likely to be replaced by fish proteins – and overfishing is already a serious issue while increased aquaculture could boost methane emissions from wetlands – and by cereal production. "The main cereal grown in India and China is rice," said Thorpe, "but rice cultivation is likely to lead to as much in terms of methane emissions as current livestock production does."

Domestic animals, particularly ruminants such as cows, sheep, goats and camels which have an additional stomach, produce large amounts of methane as they digest their food. They then belch out most of this enteric methane through their mouths. A dairy cow in New Zealand will typically produce around 80 kg of methane per year. So a herd of 200 such cows produces annual emissions roughly equivalent in energy terms to using 21,400 litres of petrol to drive a family car 180,000 km.

A number of measures has been suggested to cut methane production by livestock, for example adjusting their diet to included whole cottonseed or alfafa, using methane oxidixers as food additives, and antimethangenic vaccines. But most of these techniques are at an early stage of research and it's not yet clear whether they'll work on a large scale, if at all.

While herds in the developing world are growing, those in developed countries are shrinking. That said, the national methane budgets of New Zealand, Ireland, Luxembourg, Switzerland, Australia and Sweden are dominated by enteric emissions. What's more, national implementation of enteric methane mitigating strategies has lagged.

"As developing countries are currently exempted from the emission limitation or reduction commitments laid down in the [Kyoto] Protocol, there is presently little incentive for such countries to sacrifice foreign exchange earnings and/or enhanced domestic per capita consumption of meat by herd downsizing," said Thorpe in a paper in Climatic Change.

Only four of the Annex B countries that are obliged to conform to Kyoto overshot their methane targets by more than a marginal amount. "Hence the stimulus to pursue enteric methane mitigating strategies in order to comply with Kyoto commitments is presently weak," wrote Thorpe.

Thorpe undertook this study following an article in the popular press about a potential tax on sheep burps to fund research into mitigation measures for methane from domestic animals. "As an economist, it led me to wonder quite how this might be accomplished and so I began reading around the subject," he said. "The majority of literature, as one might expect, came from a biological angle, and it seemed that no-one had really looked at the economic implications of animal farming vis-a-vis climate change."

Thorpe is now examining how fisheries in central Asia, and the Aral Sea in particular, are being affected by changes in state regimes and climate.