Greenhouse gases that cause climate change have reached record levels in the atmosphere and show no sign of receding, despite global awareness of the need to switch to alternative energy sources, the United Nations weather agency said.

In its annual Greenhouse Gas Bulletin, the World Meteorological Organization said carbon dioxide, methane and nitrous oxide were now more prevalent in the atmosphere than at any time since the industrial revolution.

The warming effect caused by greenhouse gases - the net amount of radiation coming into the atmosphere- has increased by 29% since 1990 and 1.4% from 2009 to 2010, the last year for which data is available, the WMO said.

Last week U.N. scientists said this century will see more intense heatwaves, droughts, floods and storms because of the globally warming climate.

The WMO report measures the overall amount of greenhouse gases in the atmosphere, based on monitoring stations in more than 50 countries. That means it factors in natural emissions and absorption processes - so called "sources and sinks" - as well as emissions caused by human activity.

Carbon dioxide, responsible for 80% of the global warming effect over the past two decades, has increased rapidly with fossil fuel use. But almost half the carbon dioxide caused by fossil fuel use since 1958 has been removed by the oceans and plants on land, the report said.

The second most important greenhouse gas, methane, has been growing in the past five years after leveling off between 2000 and 2006, for reasons that are not fully understood.

The third biggest greenhouse gas is nitrous oxide, which can trap almost 300 times as much heat as carbon dioxide. Its main human source is the use of nitrogen based fertilizers, which the report said had "profoundly affected the global nitrogen cycle."

The impact of fertilizer use is so marked that more nitrous oxide is detected in the northern hemisphere, where more fertilizer is used, than in the south.

Last week's report by U.N scientists urged countries to make disaster management plans because of the threat from global warming.

However the WMO data showed no let-up in the growth of greenhouse gases, and the report's authors said more work needed to be done to help understand which policies would have the most effect.

So far, the clearest discernable impact of a policy decision was a decrease in chlorofluorocarbons, or CFCs, which were banned because they caused depletion of the ozone layer.

But hydrofluorocarbons, or HFCs, the chemicals that have replaced CFCs, are also potent greenhouse gases and their abundance in the atmosphere, while still small, is now increasing at a rapid rate.