The global mean surface temperature increased by 0.42 degrees Celsius above the 1961 to 1990 mean of 14 degrees which is used as a reference, the World Meteorological Organisation announced.

Temperatures in the highly-industrialised northern hemisphere rose faster (0.58 degrees Celsius) than in the south (0.24 degrees) and were the fourth warmest on record, according to the new data released by the WMO. 1998 was the warmest year.

The data does not include the month of December and will be finalised next February, but the ranking is unlikely to change significantly, WMO Director General Jean-Michel Jarraud said.

"There were quite a few anomalies," he added.

Key weather patterns included the warmest ever autumn in western Europe, the warmest January to September period on record in the United States, a winter that was unusually harsh or mild in different parts of the northern hemisphere, summer heatwaves, drought in China and Australia, excetionally heavy rain in parts of Africa, Latin America and severe cyclones in Asia.

The weather disruption caused historic heavy flooding, deadly storm damage, mudslides, bushfires and scorched food crops.

"Global warming doesn't mean it's going to be uniform. It may be bigger in some areas and smaller in others," Jarraud told journalists.

The WMO also confirmed the sharper seasonal melting of part of the Arctic icecap, with an area of ice bigger than Switzerland now disappearing every year.

Average sea ice in the Arctic covered 5.9 million square kilometres in September, the second lowest area on record following 2005.

"The decline is of some concern because it's occurring at a rate of about 8.6 percent per decade. That is quite a fast and significant decrease," Jarraud told journalists.

A study by US scientists published on Tuesday warned that the shrinkage of Arctic sea ice could accelerate dramatically in coming decades, leaving the planet's most northerly oceans virtually devoid of ice in summer by 2040.

The paper, which appeared in the US journal Geophysical Research Letters, mainly highlighted the impact of greenhouse-gas emissions from industry, transport and energy use.

Scientists on the International Panel on Climate Change (IPCC) warned six years ago that a significant part of global warming was caused by human activity.

The IPCC is due to publish its latest assessment reports from February 2, and Jarraud declined to comment beforehand on any links between weather patterns and temperature increases observed in 2006 and climate change.

Since the start of the 20th century, global average surface temperatures have increased by about 0.7 degrees Celsius, and the increase has accelerated in the last 30 years.

Next year the WMO will launch a major two year scientific study to examine changes in the polar regions and their link with the global climate.

"It will be one of the largest scientific experiments for many years, it will be a huge effort," Jarraud said.

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