This year is set to be one of the top-five warmest on record, according to British climate scientists.

The average global temperature for this year is expected to be more than 0.4˚C 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 this year.

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

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 Chris Folland', professor at the Met Office Hadley Centre. "Phenomena such as El Nino and La Nina have a significant influence on global surface temperature."