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 Niña, according to British climate scientists from the UK-based Met Office.

According to scientists at the Met Office and the University of East Anglia the global temperature is forecast to be more than 0.4 °C (about 1 °F) above the long-term average. This would make 2009 warmer than 2008 and the warmest since 2005.

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

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

These cyclical influences can mask underlying warming trends, explains Professor Phil Jones, Director of the Climatic Research Unit, University of East Anglia.  “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.”

El Niño is a warming of the surface water of the eastern and central Pacific Ocean, occurring every 4 to 12 years and causing unusual global weather patterns. An El Niño is said to occur when the trade winds that usually push warm surface water westward weaken, allowing the warm water to pool as far eastward as the western coast of South America.  La Niña, the opposite of El Nino, is a cooling of the surface water of the eastern and central Pacific Ocean, occurring somewhat less frequently than El Niño events but causing similar, generally opposite disruptions to global weather patterns.

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(The Met Office is a function of the United Kingdon Secretary of State for Defense, and is one of world’s leading providers of environmental and weather-related services for government and schools, broadcasters, online media, and industry including civil aviation.)