GENEVA: Greenhouse gas emissions have kept increasing, reaching a record level since the pre-industrial era, the UN climate agency warned Monday, just weeks before a crucial climate change summit.

"Levels of most greenhouse gases continue to increase," said the World Meteorological Organisation in a statement.

"In 2008, global concentrations of carbon dioxide, methane and nitrous oxide, which are the main long-lived greenhouse gases in the atmosphere, have reached the highest levels recorded since pre-industrial times," it said.

WMO Secretary-General Michel Jarraud noted that data confirmed the "tendancy of exponential increase."

"It's not really good news: concentration of greenhouse gases continue to increase, actually even a bit faster," he said.

"This is reinforcing the fact that we are actually closer to the pessimistic scenario" forecasted by scientists of the authoritative Intergovernmental Panel on Climate Change, he said.

"Action must be taken as soon as possible," he stressed, ahead of a UN summit in Copenhagen next month aimed at securing a treaty to replace the Kyoto Protocol, which aims at cutting carbon emissions.

The WMO said since 1750, atmospheric carbon dioxide -- the key driver of global warming -- has increased by 38 percent, contributing to 63.5 percent of the growth in atmospheric greenhouse effect.

In 2008, carbon dioxide levels reached 385.2 parts per million, up 2.0 ppm from a year earlier.

Methane levels stayed stable from 1999 to 2006, but showed a "significant increase" in 2007 and 2008.

Methane is over 20 times more efficient than carbon dioxide in trapping solar heat, and some 60 percent of methane arise from human influence on nature, such as rice and cattle farming, fossil fuel usage and landfills.

Meanwhile, the WMO noted that the levels of chlorofluorocarbons are decreasing as the ozone-depleting compounds are being phased out through an international treaty.

However, concentrations of substitute gases are "increasing rapidly," contributing to 8.9 percent of greenhouse effect between 2003 and 2008.