The World Meteorological Organisation says concentrations of the main greenhouse gases in the atmosphere have reached their highest level since pre-industrial times.
The United Nations weather agency says concentrations of carbon dioxide, methane and nitrous oxide continued to build up in 2009 - the latest year of observations - despite the economic slowdown.
WMO said total radiative forcing of all long-lived greenhouse gases increased by 1.0% in 2009 and rose by 27.5% from 1990 to 2009.
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.
The findings will be studied at a UN meeting on climate change in Cancun, Mexico, from 29 November - 10 December.
