Levels of atmospheric carbon dioxide hit an all-time high last year, with 393.1 parts per million recorded - 141% of the pre-industrial level of 278 parts per million.
The World Meteorological Organisation's annual Greenhouse Gas Bulletin also found levels of methane and nitrous oxide reached record levels in 2012.
Researchers found there was an "upward and accelerating trend" of greenhouse gas emissions that is driving climate change and will shape the planet's future for centuries to come.
The report found that between 1990 and 2012, radiative forcing (the warming effect on climate) through greenhouse gasses increased by a third, with CO2 accounting for 80% of this increase.
It also found atmospheric increase in CO2 between 2011 and 2012 was higher than the average growth rate of the last 10 years.
Monthly observations of CO2 exceeded 400ppm at several Global Atmosphere Watch stations in 2012.
At the current rate of increase, the global average annual atmospheric CO2 level is set to cross the 400 parts per million threshold by 2015 or 2016.
When the 400ppm threshold was crossed last year, Christina Figueres, secretary of the UN Framework Convention on Climate Change, said: "With 400 ppm CO2 in the atmosphere, we have crossed an historic threshold and entered a new danger zone.
"The world must wake up and take note of what this means for human security, human welfare and economic development. In the face of clear and present danger, we need a policy response which truly rises to the challenge."
Michael Jarraud, secretary general of the WMO, said the latest report once again highlights how "heat-trapping gasses from human activities" are upsetting the natural balance of the atmosphere.
"The Intergovernmental Panel on Climate Change (IPCC) in its recent 5th Assessment Report stressed that atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.
"As a result of this, our climate is changing, our weather is more extreme, ice sheets and glaciers are melting and sea levels are rising.
"According to the IPCC, if we continue with "business as usual", global average temperatures may be 4.6 degrees higher by the end of the century than pre-industrial levels - and even higher in some parts of the world. This would have devastating consequences.
"Limiting climate change will require large and sustained reductions of greenhouse gas emissions. We need to act now, otherwise we will jeopardize the future of our children, grandchildren and many future generations. Time is not on our side."