Belching cows are making a rapidly growing contribution to global warming, a university researcher said today.
Dr Andy Thorpe, an economist at the University of Portsmouth, explained that a herd of 200 cows burp the annual equivalent amount of methane to the energy produced by a family car being driven 180,000km using 21,400 litres of petrol.
He added that while carbon dioxide (CO2) emissions have increased by 31% during the past 250 years, methane, which has a higher warming potential and a longer lifetime in the atmosphere, has increased by 149% during the same period.
Dr Thorpe added that methane in the atmosphere was believed to be responsible for one fifth of global warming experienced since 1750.
The main animal producers are domestic animals, particularly cows, sheep, goats and camels which have an additional stomach, he said.
They produce large amounts of methane as they digest their food and then belch out most of it through their mouths.
A dairy cow in New Zealand will typically produce about 80kg of methane per year.
Dr Thorpe explained that much of the methane increase was taking place in the developing world where cows and other domestic animals were often bred to feed the developed world.
He said: “Methane emission growth, like CO2 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.
“If anything, methane emissions in the developing world are likely to increase.”
Dr Thorpe said that methane was covered by the Kyoto Protocol on climate change but much of the developing world had not signed up to the agreement.
He explained that up to 75% of animal methane emissions came from developing countries, with India and Brazil being the leading producers.
He said that efforts were being made to reduce the emissions, including providing different feed and using vaccinations, but added that they were in early stages of research.
And he said there could be problems with down-sizing herds as working animals could end up being replaced by petrol-driven vehicles and a reduction in meat could lead to a “disastrous” increase in demand for fish and cereals.
Dr Thorpe, whose paper has been published in the journal Climatic Change, said: “Developing countries are exempt from the Kyoto Protocol’s bid to limit emissions so there is currently little incentive for them to sacrifice foreign exchange earnings and/or eat less meat by herd down-sizing.”
Each year, around 600 teragrammes of methane is produced worldwide with between 55 and 70% coming from man-made sources.