From: Reuters
Published February 11, 2008 10:16 AM

La Nina Pacific cooling may last to mid-year: U.N.

By Robert Evans

GENEVA (Reuters) - A sea-surface cooling in the Pacific, which may have contributed to strong hurricanes in the United States and a freeze-up in China, could last at least until mid-year, the U.N. weather body WMO said on Monday.

The cooling pattern, known as La Nina, alternates naturally with a warming effect called El Nino, and both have been associated with extreme weather around the globe.

"Information coming in indicates that the likelihood of La Nina conditions in the central and eastern Pacific remains heightened through the second quarter," said Rupa Kumar Kolli, climatological expert at the World Meteorological Organisation.

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Presenting the Geneva-based body's latest update on the ocean cycle, he said it was also possible, if less likely, that the present La Nina cycle could stretch into the third quarter.

Longer-term statistics suggested that the decline of the La Nina would be followed by a "neutral" period at least for the second half of 2008, Kolli added, rather than a rapid transition to an El Nino.

The two closely linked natural phenomena have probably occurred since before recorded history and are popularly blamed for unusual weather extremes, but specialists say they are not the sole cause.

Kolli said the two, which follow each other with a neutral break in between, create favorable conditions for changing local and regional weather patterns around the globe to spark floods, droughts, hurricanes and freeze-ups.

Meteorologists say the nearly month-long Chinese snow and ice-storms at the start of this year, which killed scores of people and cost the economy at least $7.5 billion, were partly caused by a cold surge from the north and west.

El Nino -- "the Boy Child" in Spanish -- got its name because it generally starts in December, the month in which Christians who predominate in Latin America celebrate the birth of Christ. La Nina means "the Girl Child."

Experts say it is not clear if the El Nino/La Nina cycle -- which occurs around once every five years -- is intensified by global warming, but they say it makes it more likely that climate changes caused by warming will bring disasters.

In an El Nino, the sea surface heats up, leading to drier than normal weather over northern Australia, the Philippines and Indonesia and wetter conditions than usual over much of Latin America and in parts of the United States and Africa.

In La Nina, these regional patterns are reversed.

Both also contribute to abnormal temperature swings around the globe, especially during the December-April period when they are strongest, experts say. El Nino generally helps bring hotter weather than normal and La Nina leads to unusual cold.

The last El Nino, whose intensity caused devastation along the western coast of North and South America in 1997-98, lasted for nearly 12 months, just slightly more than average.

The La Nina which followed lasted nearly 2 years. The current one started in the third quarter of 2007.

(Editing by Jonathan Lynn and Mark Trevelyan)

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