GENEVA, Nov. 23 (Xinhua) -- Globally averaged concentrations of carbon dioxide (CO2) in the atmosphere reached their highest levels ever recorded in 2006, the World Meteorological Organization (WMO) said on Friday.

In its 2006 Greenhouse Gas Bulletin, the UN agency said global CO2 levels in the atmosphere reached 381.2 parts per million (ppm), up 0.53 percent from 379.2 ppm in 2005.

The information is based on observations from the WMO Global CO2 and CH4 Monitoring Network, a comprehensive climate network recognized by the United Nations Framework Convention on Climate Change.

After water vapor, carbon dioxide, methane (CH4) and nitrous oxide (N2O) are the three most prevalent greenhouse gases in the Earth's atmosphere respectively.

Greenhouse gases are major drivers of global warming and climate change.

According to the WMO, concentrations of N2O also reached record highs in 2006, up 0.25 percent from 319.2 parts per billion (ppb) to 320.1 ppb, while methane remained almost unchanged at 1,782 ppb.

The 36 percent rise in CO2 since the late 1700s has largely been generated by emissions from the combustion of fossil fuels.

Around one third of N2O discharged into the air is a result of human activities such as fuel combustion, biomass burning, fertilizer use and some industrial processes.

Human activity such as fossil fuel exploitation, rice agriculture, biomass burning, landfills and ruminant farm animals account for some 60 percent of atmospheric CH4, with natural processes including those produced by wetlands and termites responsible for the remaining 40 percent.