The main greenhouse gases have reached their highest concentration levels since pre-industrial times, a United Nations climate research body said Wednesday.

The World Meteorological Organization's (WMO) 2009 Greenhouse Gas Bulletin warns that carbon dioxide, methane and nitrous oxide have all increased their presence, increasing their burden on the earth's atmosphere.

"Greenhouse gas concentrations have reached record levels despite the economic slowdown. They would have been even higher without the international action taken to reduce them," said WMO Secretary-General Michel Jarraud.

According to the Bulletin, the prevalence of all major greenhouse gases increased by 27.5 per cent from 1990 to 2009 and by a further 1.0 per cent from 2008 to 2009.

Since 1750, carbon dioxide's presence in the atmosphere has increased by 38 per cent, primarily because of emissions from fossil fuels combustion, deforestation and changes in land-use. Methane's prevalence has increased over the same period by 158 per cent. Sixty per cent of methane emissions are caused by human activity.

The report highlights concerns that global warming may lead to even greater natural emissions of methane from Arctic areas.

"Potential methane release from northern permafrost, and wetlands, under future climate change is of great concern and is becoming a focus of intensive research and observations," Mr. Jarraud said.

The WMO is the UN system's authoritative voice on weather, climate and water. It coordinates the UN's observations of greenhouse gases in the atmosphere. Every year since 2004, the body has produced a Greenhouse Gas Bulletin, which reports on the latest status and changes in atmospheric burdens of the main greenhouse gases.