GENEVA - Concentrations of the main greenhouse gases in the atmosphere have reached their highest level since pre-industrial times, the World Meteorological Organization said on Wednesday.

Concentrations of carbon dioxide, methane and nitrous oxide continued to build up in 2009 -- the latest year of observations -- despite the economic slowdown, the United Nations weather agency said in its latest Greenhouse Gas Bulletin.

Increasing amounts of the long-living greenhouse gases in the atmosphere cause global warming and hence climate change.