"Climate change is taking place before our eyes and will continue to do so as a result of the concentrations of greenhouse gases in the atmosphere, which have risen constantly and again reached new records," said Michel Jarraud, the chief of the Geneva-based UN agency.

The WMO's preliminary climate report for this year said that the ice area around the North Pole shrunk to 3.41 million square kilometres in September, 18 per cent less than the previous low in 2007.

Arctic ice expands every year in the cold season and shrinks between March and September.

Globally, 2012 has been the ninth-hottest year since records began in 1850 and it is expected to become the hottest on record in the United States, the WMO said.

Above-average temperatures and extreme weather have affected most world regions since January, especially in the northern hemisphere.

While heat waves, droughts and cold spells hit many northern regions, floods swept through western Africa and the Sahel, as well as southern China, Pakistan, Argentina and Colombia.

For the third year in a row, the hurricane season in the Atlantic was more intense than the 20-year average, according to UN weather experts.