Yahoo News 25 Jan 11;
GENEVA (AFP) – The weather pattern behind floods and extreme conditions in Australia, Asia, Africa and South America is one of the strongest ever and could last for four more months, the UN weather agency said Tuesday.
"In atmospheric terms it has to be termed one of the strongest ever La Nina episodes," said Rupa Kumar Kolli, head of world climate services at the UN's World Meteorological Organisation (WMO).
"The most important impacts we have witnessed in recent months have been the devastating floods in Australia," he told journalists.
The Geneva-based WMO said in its latest update that "a significant La Nina episode" was continuing in the tropical Pacific Ocean "with effects extending onto adjacent ocean basins."
All scientific predictions forecast "a continuation of the current La Nina for at least the next two to four months," it added, although the climate pattern was likely to progressively weaken over that period.
"Even if we expect La Nina to weaken over the next few months, the impacts are likely to continue," Kumar Kolli cautioned.
Apart from flooding in Australia and wetter weather in western Pacific, the WMO is linking La Nina to wetter than normal conditions in southern Africa, drought in east Africa and the western seaboard of South America.
Kumar Kolli also drew a direct link with deadly landslides in Brazil and flooding in Sri Lanka for the first time even though they were "atypical impacts" of the disruptive weather pattern.
La Nina atmospheric currents that emerged last summer probably combined with other local influences from the Atlantic or Indian Oceans in those instances, he suggested.
La Nina is characterised by unusually cool ocean temperatures in the central and eastern tropical Pacific and typically lasts about nine months.
However, the complex interaction between shifting ocean currents and the atmosphere, and its range remain little understood by scientists, who are also reluctant to establish a clear tie with climate change.
In term of its atmospheric effects -- such as on winds, clouds and pressure systems -- the current La Nina ranked about third strongest for the past century on one scale, while its cooling of Pacific Ocean temperatures was rated as moderate to strong, Kumar Kolli explained.
La Nina Likely To Persist Through First Quarter
Stephanie Nebehay PlanetArk 27 Jan 11;
The weather pattern known as La Nina, blamed for floods in Australia and drought in parts of Latin America, is expected to persist through the first quarter of 2011, the World Meteorological Organization said on Tuesday.
La Nina, which cools the Pacific Ocean, could possibly even continue into April or early May, further affecting weather around the globe, the United Nations agency said in its latest update.
"Almost all forecast models predict a continuation of the current La Nina for at least the next 2-4 months, through the first quarter of 2011 and possibly into the second quarter (April or early May)," the WMO said.
"The strength of the event is likely to decrease during the course of the coming 4 months," it added.
La Nina began last June following a strong El Nino event in the Pacific Ocean, a naturally occurring and opposite weather phenomenon associated with warmer-than-normal water.
In terms of its effects on the atmosphere -- sea level pressure, stronger trade winds and much reduced cloudiness -- this La Nina is "one of the strongest of the last century," according to the WMO.
However, in terms of its oceanic effects, it is rated to have been moderate to strong. It caused sea surface temperatures to average around 1.5 degrees Celsius (2.7 Fahrenheit) less than normal in the eastern and central tropical Pacific.
"We know that even if the La Nina is likely to weaken over the next few months, the impacts are likely to continue in the regions typically influenced by this phenomenon," WMO expert Rupa Kumar Kolli told a news briefing.
"The most important impacts that we have witnessed during the recent weeks have been devastating floods in Australia."
Floods have ravaged huge areas of eastern Australia, killing at least 25 people, submerging parts of the nation's third-largest city, Brisbane, shutting vital coal mines and destroying crops.
La Nina had also led to above-average rainfall in Indonesia, southeast Asia and southern Africa.
"La Nina is not associated with floods alone, it is also associated with droughts in some parts of the world, particularly in South America, in the coastal regions, particularly the west coast of Peru and Ecuador and adjoining areas," Kolli said.
But some impacts had been unusual, including floods in Sri Lanka and Brazil, where conditions in the Indian and Atlantic Oceans may have also played a role, he said.
La Nina occurs every 2-7 years, lasting 9-12 months, but there is no clear information on long-term trends, he said.
"The available information -- we have more than 100 years of recorded data -- does not indicate any clear evidence of these events being more frequent or more intense," he said.
(Editing by Jonathan Lynn and Mark Trevelyan)
