Experts predict a run of severe weather in the coming months, with devastating floods striking some parts of the world while severe droughts afflict other regions, as the climate phenomenon known as La Niña gathers momentum.
Rupa Kumar Kolli, chief of world applications at the World Meteorological Organisation (WMO) in Geneva, predicts that the worst of La Niña is yet to come. “This La Niña is now in its developing phase and getting stronger, and we can expect it to peak this coming December and January,” he said.
Met Office scientists have found that La Niña is likely to have played a part in the abysmal British summer. By upsetting the usual track of the high-altitude jet stream towards Britain, it delivered barrages of slow-moving Atlantic depressions with torrents of rain. La Niña may also have been involved in the spectacular Asian monsoon this summer, leading to floods that killed about 1,000 people in India and Bangladesh.
La Niña occurs when the tropical seas of the Pacific off the coast of Latin America cool down, while the waters turn warmer towards Australia, the Philippines and Indonesia. That lurch in ocean temperatures can send weather systems into havoc over vast areas, delivering huge deluges of rain over the Far East and tropical Australia, while western parts of Latin America turn much drier than usual. This is the flip side of El Niño, although La Niña lasts for a shorter time, usually no more than a year.
The way that La Niña casts its spell over the globe, from the Pacific to the rest of the world, is known as a “tele-connection”. By disrupting sea temperatures, pressure systems and winds over the Pacific, it interferes with the atmospheric circulation around the tropics. This sends out waves in the atmosphere, like casting a stone into a pond, which can change the strength and position of jet stream winds several miles high. In this way the Pacific can have a huge impact on the weather far from the tropics.
Source: The Times