Thursday 29 October 2020

2020 La Niña

Fed up with bad news about The 'Rona? What about La Niña? ready for some hardship from The Girl?

Well might the anchoveta Engraulis ringens feature on an issue of Peruvian stamps. A lot of Peruvian citizens depend on its appearance within cruising distance of the coast. When the anchoveta appear they are absurdly abundant: annual landings of just this species are in the millions of tonnes. Typically, the fishing fleet consists of purse-seiners: about 75% of the catch lands in Peru, the rest in Chile.
The Bonanza year was 1971 when 13,000,000 tonnes were caught: it's been up and down since then but the trend is down because fishing is the classic case of the Tragedy of the Commons: if more than two people are involved, it's hard to resist the urge to catch one more fish. The Peruvian fisheries can predict whether is will be a good year for epipelagic fish by the simple expedient of taking the water temperature at the surface and 50m down. Actually, a long interesting discussion suggests vice-versa that the fish can predict the weather

If it's warm then it's an El Niño year, warm water means less dissolved oxygen. Apart from weird life but not as we know it Jim abyssal ecosystems around hydrothermal vents on the Ocean floor, everything depends on oxygen because Prochlorococcus [prev] depends on oxygen to do its foundational photosynthesis. El Niño is named for the Christ-child because Christmas was peak-anchovy . . . if there were any to be had at all. 
Some years are El Niño events but a smaller number are La Niña years. That's when persistent off-shore winds barrel down off the Andes and sweep all the warm surface water out into the middle of the Pacific Ocean. Think Kon-Tiki? They are replaced by a massive up-welling of colder, oxygen- and nutrient- rich water from the depths; Prochlorococcus goes exponential and gets eaten by herbivorous plankton, which get eaten by carnivorous plankton and so up the food chain to anchovies . . . and beyond! - skipjack tuna Katsuwonus pelamis and blue fin Thunnus orientalis and, of course, the alpha predator Homo sapiens all have a field day.
Now I dare say you are quite Frankly Scarlett about the livelihoods of Peruvian fisherfolk. But you should be aware that weather depends inordinately on the temperature of sea water. A small increase, say 1°C, over millions of hectares of sea is a heckuva lot of calories/Joules of energy and a proportion of that will make the air above a lot more active. Think hurricane season in the sub-tropics: global warming is going to deliver many more of them before we're all dead.
In over-simplified terms [because that's all I can manage!], a lot of cold surface water along the Panama coast in La Niña years - like this year - means that the Caribbean is less windy which stops The Weather tramping across the Atlantic throwing shapes. These weakened incommming Westerlies barely reaching the European Altantic coastline allows big lumps of very cold air from Siberia to move Westwards and envelope Ireland and the rest of the Western European Archipelago in frost, ice, snow-drifts and woeful driving conditions. Remember the Emmalo? Storm Emma Feb/Mar 2018. The Great Thaw of Feb 2010, was the end of the coldest Winter since 1962-63
Just sayin'! I can't be wronger or randomer than the Donegal postman.

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