LONDON (Reuters) - Next year is set to be one of the top-five warmest on record, British climate scientists said on Tuesday.

A man walks under the rising sun on Manly Beach in Sydney November 22, 2006. REUTERS/Will Burgess

The average global temperature for 2009 is expected to be more than 0.4 degrees celsius above the long-term average, despite the continued cooling of huge areas of the Pacific Ocean, a phenomenon known as La Nina.

That would make it the warmest year since 2005, according to researchers at the Met Office, who say there is also a growing probability of record temperatures after next year.

Currently the warmest year on record is 1998, which saw average temperatures of 14.52 degrees celsius - well above the 1961-1990 long-term average of 14 degrees celsius.

Warm weather that year was strongly influenced by El Nino, an abnormal warming of surface ocean waters in the eastern tropical Pacific.

Theories abound as to what triggers the mechanisms that cause an El Nino or La Nina event but scientists agree that they are playing an increasingly important role in global weather patterns.

The strength of the prevailing trade winds that blow from east to west across the equatorial Pacific is thought to be an important factor.

“Further warming to record levels is likely once a moderate El Nino develops,” said Professor Chris Folland at the Met Office Hadley Center. “Phenomena such as El Nino and La Nina have a significant influence on global surface temperature.”

Professor Phil Jones, director of the climate research unit at the University of East Anglia, said global warming had not gone away despite the fact that 2009, like the year just gone, would not break records.

“What matters is the underlying rate of warming,” he said.

He noted the average temperature over 2001-2007 was 14.44 degrees celsius, 0.21 degrees celsius warmer than corresponding values for 1991-2000.