Greenhouse gases in the Earth's atmosphere reached record highs in 2008, with carbon dioxide levels increasing faster than previously, the UN weather agency said Monday in Geneva.

Levels of greenhouse gases, believed to be responsible for global warming, have been rising every year since detailed records started being kept in 1958, the World Meteorological Organization said.

It follows a trend of rising emissions that began with the Industrial Revolution in the mid-18th century, the agency said. 

The report comes as the European Union urged the United States and China on Monday to set targets for cutting greenhouse gas emissions at next month's climate conference in Copenhagen. The European Union said delays by those countries were hindering global efforts to curb climate change.

The gases — carbon dioxide, or CO2; nitrous oxide, N2O; and methane, CH4 — are produced partly by natural sources, such as wetlands, and partly by human activities such as fertilizer use or fuel combustion.

"Concentration of greenhouse gases continued to increase, even a bit faster," the organization's chief, Michel Jarraud, told reporters in Geneva.

Carbon dioxide — the main greenhouse gas in the atmosphere — was 385.2 parts per million in 2008, up two parts per million from 2007, the report said.

The CO2 content in the atmosphere rose slightly faster in 2008 than over the last decade when the growth rate was 1.9 parts per million, Jarraud said. "It's significant because what we would like is to see a decrease."

Nitrous oxide increased by 0.9 parts per billion over the previous year to 321.8 parts per billion. Methane concentration in the atmosphere was 1,797 parts per billion, up seven parts per billion from the previous year.

The year-to-year increase may appear small. But compared to the time before the Industrial Revolution, the levels have increased massively, the WMO said.

Since 1750, CO2 has increased 38 per cent, nitrous oxide 19 per cent and methane 157 per cent, according to WMO.