In its annual Greenhouse Gas Bulletin released on Tuesday, the organisation said that carbon dioxide levels reached 391 parts per million in 2011.
The report estimates that carbon dioxide accounts for 85% of the "radiative forcing" that leads to global temperature rises.
Other potent greenhouse gases such as methane also reached record highs. The carbon dioxide levels appear to have been rising at a level of two parts per million each year for the last 10 years - with the latest measure being 40% higher than those at the start of the industrial revolution.
The WMO estimates that 375 billion tonnes of carbon have been released into the atmosphere since 1750, and that about half of that amount is still present in the atmosphere.
"These billions of tonnes of additional carbon dioxide in our atmosphere will remain there for centuries, causing our planet to warm further and impacting on all aspects of life on Earth," said WMO Secretary-General Michel Jarraud.
"Future emissions will only compound the situation."
US weather agency the National Oceanographic and Atmospheric Administration (NOAA) contributed to the bulletin with their Annual Greenhouse Gas Index, which indicated that between 1990 and 2011, carbon dioxide's role in the radiative forcing that leads to warming had increased by 30%.