Magazine article Geographical

All about Little Boys and Girls

Magazine article Geographical

All about Little Boys and Girls

Article excerpt

Any climatic quirk these days is put down to El Nino. But as Nick Middleton explains the talk is not all hot air

If it's not global warming then it must be El Nino. That's the explanation for virtually any unusual weather event or climatic quirk nowadays. Whether it's a forest fire in Southeast Asia or a flood in South America, a devastating drought in southern Africa or a bad winter in Europe, someone will look at you knowingly and cite the magic mantra: "El Nino".

Well, maybe so and maybe not. El Nino has been wrongly blamed for just about everything from the extinction of the dinosaurs to domestic squabbles, but it is true to say that this phenomenon affects the weather across many parts of the planet. The 1997/98 El Nino, the most dramatic recorded to date, was thought to be responsible for record rainfall in China, heavy flooding in Peru, drought and wildfires in Indonesia, crop failure in Zambia and Cuba, tornados in southeast USA and loss of life and property damage in numerous other parts of the world. The propensity for a natural event in the South Pacific to affect the weather elsewhere in the world is dubbed by climatologists `global teleconnections'.

The term El Nino was first coined by Peruvian fishermen in the nineteenth century. It means `the boy child' in Spanish and they used it to refer to a distinct warming of the surface sea water. This warming happened around Christmas time and was often associated with an abrupt decrease in the abundance of fish in the sea. Perhaps they thought that such a marked change in Nature's bounty was God's doing, so they named it after his son.

In order to understand just what El Nino entails, and how it works, it's useful to look at what happens to the ocean surface and the air above it when an El Nino isn't happening. The waters of the South Pacific off the coast of Peru are usually rich fishing grounds, home to the Peruvian anchovy, one of the largest fisheries in the world. This is because this part of the South Pacific is an area of great `upwelling' of relatively cool water from the ocean depths to the surface. Such regions of upwelling are often very rich in nutrients, making them highly fertile, hence the abundant fish stocks.

Another direct result of the relatively cool surface waters is a stable atmosphere above: hot air rises, cool air does not. A stable atmosphere means high pressure at the earth's surface and rain seldom falls. The coasts of Peru and its southern neighbour Chile make up the driest desert on earth: the Atacama.

The cold upwelling along the Atacama coastline is driven by the trade winds that blow westward across the tropical Pacific. Travel for 10,000 kilometres and you come to northern Australia and Indonesia, where these winds pile up warm surface water. The level of the sea surface is about half a metre higher at Indonesia than at Peru, and the sea surface temperature is much warmer. This warm the atmosphere above, resulting in unstable air and low pressure at the earth's surface. The climate here is usually characterised by high rainfall.

This pattern of oceanic and atmospheric circulation in the South Pacific region, and its associated distribution of surface pressure, was first studied in detailed by Sir Gilbert Walker, a British meteorologist. It is called the Walker Circulation. …

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