ABC News Online, 25 November 2010
The World Meteorological Organisation (WMO) says concentrations of the main greenhouse gases in the atmosphere have reached their highest level since pre-industrial times.
Concentrations of the gases continued to build up in 2009 - the latest year of observations - despite the economic slowdown, the UN weather agency said in its latest Greenhouse Gas Bulletin.
Rises in the amount of greenhouse gases increase radiation in the atmosphere, warming the surface of the Earth and causing climate change.
"The main long-lived greenhouse gases including carbon dioxide, methane and nitrous oxide, have reached their highest recorded levels since the beginning of the industrial age, and this [is] despite the recent economic slowdown," WMO deputy secretary general Jeremiah Lengoasa said.
Total radiative forcing of all long-lived greenhouse gases - the balance between radiation coming into the atmosphere and radiation going out - increased by 1.0 per cent in 2009 and rose by 27.5 per cent from 1990 to 2009, the WMO said.
The growth rates for carbon dioxide and nitrous oxide were smaller than in 2008, but this had only a marginal impact on the long-lasting concentrations.
Carbon dioxide is the single most important greenhouse gas caused by human activity, contributing 63.5 per cent of total radiative forcing.
Its concentration has increased by 38 per cent since 1750, mainly because of emissions from burning fossil fuels, deforestation, and changes in land use, the WMO said.
Natural emissions of methane due, for example, to the melting of the Arctic icecap or increased rainfall on wetlands - themselves caused by global warming - are becoming more significant, it said.
This could create a "feedback loop" in which global warming releases large quantities of methane into the atmosphere which then contribute to further global warming.
These natural emissions could be the reason why methane has increased in the atmosphere over the past three years after nearly a decade of no growth, the WMO said.
Human activities such as cattle-rearing, rice planting, fossil-fuel exploitation and landfills account for 60 per cent of methane emissions, with natural sources accounting for the rest.