The climate phenomenon known as La Nina sets off a chain reaction among weather patterns the world over. That can lead to more drought in some places even as it produces flooding and hurricanes in others. La Nina occurs when the surface of the Pacific Ocean along the equator cools and the atmosphere above it reacts. Typically, it happens once every few years. However, the persistence of the most recent case poses the likelihood that the Northern Hemisphere will see its third La Nina winter in a row, a rarity.
1. How unusual is this?
Since 1950, according to US records, a La Nina in three consecutive years has occurred only twice, in the periods 1998-2001 and 1973-1976. As far as anyone knows there has never been a four-time La Nina, so forecasters believe the current one will fade in early 2023 after it peaks.
2. What could a third year of La Nina mean?
For California, the biggest farming state in the US, and for the soybean- and corn-growing areas of Argentina and Brazil, it could mean another year of drought. In Australia, it might bring another round of floods across Queensland, Victoria, and New South Wales, where rising waters produced at least $3 billion in insurance claims in early 2022. The price of a cup of coffee could climb if drought afflicts farmers in Brazil while floods hit those in Vietnam and Columbia. Sugar to sweeten it might also cost more if the cane used to make it gets stressed by a lack of rain. Across the Atlantic, there could be even more hurricanes than usual because there, La Nina cuts down on wind shear, one of nature’s ways of putting a break on the destructive storms. In 2020, the Atlantic had a record 30 named storms, and in 2021 there were 21.
3. How does La Nina relate to El Nino?
La Nina is part of a bigger cycle known as El Nino-Southern Oscillation. ENSO, as scientists call it, is made up of El Nino -- so named by Peruvian fishermen for the Christ child in the 1600s when they noticed the tropical Pacific warming around Christmas some years, La Nina, and a neutral phase in between.
4. What causes this cycle?
El Ninos occur for reasons unknown, although some scientist think they are a way for Earth’s atmosphere to shed heat into space. They begin with a weakening in the trade winds that push the sun-warmed waters of the equatorial Pacific into a mound in the west. Some of that water flows back east, making the eastern Pacific hotter. The phenomenon affects larger wind currents, shifting moisture-bearing storms away from some places, such as Indonesia and Africa, and toward others, including Argentina and Japan. When the heat from El Nino is spent, the ocean begins to cool. Initially, the Pacific falls into a state between the extremes, the neutral phase. If the cooling continues and sea surface temperatures fall below normal, La Nina occurs. The whole thing tends to play itself out every two to seven years. As has been evident since 2020, however, one end of the pattern can dominate for a time. The Atlantic and Indian oceans have similar events but theirs don’t have the far-reaching impact of those in the immense Pacific.
5. Is climate change affecting the cycle?
Some early models had suggested that as the Earth warmed, the number of El Nino events would rise. However, that doesn’t seem to have happened. So far this century, La Nina has dominated the cycle. It will take more research to tease out why, weather experts say. One theory is that smoke from wildfires in Australia in 2019 and 2020 are a factor, according to Gerald Meehl, senior scientist at the National Center for Atmospheric Research in the US. There are so many variables influencing El Nino and its ramifications, US government meteorologist Tom Di Liberto noted years ago, isolating the role of global warming may not be possible.
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