2009 is expected to be one of the top-five warmest years on record, despite continued cooling of huge areas of the tropical Pacific Ocean, a phenomenon known as La Nina.

According to climate scientists at the Met Office and the University of East Anglia (UEA) the global temperature is forecast to be more than 0.4 C above the long-term average. This would make 2009 warmer than the year just gone and the warmest since 2005.

During La Nina, cold waters rise to the surface to cool the ocean and land surface temperatures. The 2009 forecast includes an updated decadal forecast using a Met Office climate model. This indicates a rapid return of global temperature to the long-term warming trend, with an increasing probability of record temperatures after 2009.

Professor Chris Folland from the Met Office Hadley Centre said: "Phenomena such as El Nino and La Nina have a significant influence on global surface temperature. Warmer conditions in 2009 are expected because the strong cooling influence of the recent powerful La Nina has given way to a weaker La Nina. Further warming to record levels is likely once a moderate El Nino develops."

These cyclical influences can mask underlying warming trends as Professor Phil Jones, Director of the Climatic Research Unit, University of East Anglia, explains: "The fact that 2009, like 2008, will not break records does not mean that global warming has gone away. What matters is the underlying rate of warming - the period 2001-2007, with an average of 14.44 C, was 0.21 C warmer than corresponding values for the period 1991-2000."

The Met Office, in collaboration with UEA, maintains a global temperature record which is used in the reports of the Intergovernmental Panel on Climate Change. Each January the Met Office, in conjunction with the University, issues a forecast of the global surface temperature for the coming year. The forecast takes into account known contributing factors, such as El Nino and La Nina, increasing greenhouse gas concentrations, the cooling influences of industrial aerosol particles, solar effects and natural variations of the oceans.

Global temperature for 2009 is expected to be 14.44C, the warmest since 2005, when the value was 14.48C. The warmest year on record is 1998, which was 14.52C, a year dominated by an extreme El Nino.