Gas emissions from flatulent cows could soon be restricted by a EU quota system as penal as that imposed on milk production, an agricultural expert has predicted.

Environmental scientist Professor Frank Convery claims cows breaking wind and belching account for 35% of Ireland's green-house gas emissions. These have been linked to global climate change.

"When you have an agricultural economy - we have over eight million cows in the Republic of Ireland - you end up producing a lot of greenhouse gas. It's similar in Northern Ireland," he said.

At present the limit in the Republic of Ireland for the production of carbon gases is 64.5m tonnes. Current emissions are exceeding this limit amid growing concern that the levels would increase further due to the growth of the Irish economy with more vehicles on the road.

Professor Convery told a conference in Dublin he believes the short-term solution to the problem could be a EU penalty similar to the that imposed on farmers who exceed limits on milk production.

Other possible solutions include imposing dietary changes on cows and forcing them to feed indoors.

There are difficulties with this option, however, according to the professor. "We pride ourselves on grass fed cattle, grazing in the open air, full of natural goodness," he said.

In the longer term, the solution could be the creation of a global market for "carbon trading", said Professor Convery, who is working at University College Dublin's Environmental Instittue.

This is expected to be formed within 10 years and would enable countries to regulate the levels of emissions, the Agmet conference on the effects of agriculture on the climate was told.

Under "carbon trading" farmers could gain credit by investing in afforestation or measures to recover the methane gas emitted by cows.

Those wishing to get out of farming could sell the resulting reduction in greenhouse gas production.

Flatulence and belching by cows derive from a process known as enteric fermentation which leads to a build up of methane gas in the guts of these animals, pressure which is relieved by emission.

Professor Convery says other animals can also contribute to the accumulation of greenhouse gases but, due to their size and appetites, cattle are the main offenders.