"This year is likely to be in the top five, probably about the fifth warmest worldwide," said David Viner, senior climate scientist at the British University of East Anglia.

But some earlier parts of the year were cooler and experts say that 2006 will not beat all-time global records -- 1998 or 2005 -- since reliable records began in the 1860s.

The UN's World Meteorological Organisation (WMO) says the 10 years 1996-2005, with the exception of 1996, are the warmest on record with 1998 the most sweltering.

NASA, by contrast, reckons that 2005 was hottest ahead of 1998.

"We do not expect 2006 to be as warm as 2005, so not the warmest on record," said Drew Shindell of the NASA-Goddard Institute for Space Studies in New York.

NASA and WMO data differed slightly "due to choices about satellite data over the Arctic, but the differences were small for most purposes," said Shindell.

"The overall picture of a warming planet with a 'noisy' trend is quite consistent," he said.

As temperatures rise Arctic perennial sea ice, the kind that stays frozen year-round, shrinks. The ice was 6 percent smaller in 2005 and 2006 than the average over the past 26 years, according to NASA. As ice recedes, darker ground and sea absorbs ever more heat.

The WMO declined to give a prediction about where 2006 would rank, saying it will issue its temperature overview on Dec. 14.

Most scientists say that world temperatures are creeping higher because of human emissions of greenhouse gases, mainly from burning fossil fuels in power plants, factories and vehicles.

Viner said that 1998 was unusually warm partly because of the El Nino warming in the tropical Pacific. That extreme El Nino was blamed for killing hundreds of people across the Asia-Pacific region.