weather
The bandit weather system El Ni —o is so unpredictable that scientists can’t predict whether it’s even going to happen, writes Julia Grey
YOU can rely on the sun to rise, and the seasons to tick over predictably, but in some cases, nature is not so straightforward. It’s even possible that the breath of a butterfly’s wings in the Amazon can set off a chain of events resulting in a typhoon flattening Fiji.
Is nature really so random and unpredictable? The struggle of scientists to accurately predict and explain the weather suggests that it is. The bandit weather system, El Ni —o, is an interesting case in point.
For those uninitiated in the realm of climatology, El Ni —o is a phenomenon originating from the Pacific ocean that is hugely influential on weather across our planet.
As far back as the 1800s, the locals in Peru (who named the annual event of a local warming of the Pacific “El Ni —o”, or “the boy”, because it occurred around Christmas time) recognised how temperature changes in the Pacific affected weather conditions. And since the late 1960s, scientists have gradually been piecing together the puzzle of how events in the atmosphere and the oceans can work together to wreak large-scale havoc with the world’s weather patterns.
In a La Nina year (the opposite of El Ni — -o, meaning “the girl”), the average conditions are exaggerated – so in a wet region, heavier rainfall will be experienced, and vice versa. El Ni —o, by contrast, generally causes a reversal of what’s normal – so in places where it is usually dry, heavy rainfall is experienced, while the opposite happens in usually wet regions.
The past 15 years have been dominated by successive El Ni —os – and its effects have been devastating. The hugely powerful El Ni —o experienced in 1982-83 – described as a “maverick” El Ni —o because it caught scientists totally by surprise – is said to have cost the world’s economy over $8-billion.
Current international speculation has it that we may once again be in for an El Ni – –o this year. But, according to Dr Simon Mason from the Wits Climatology Research Group, there is at present “a disappointing range of forecasts” around the El Ni —o that seems to be developing in the Pacific ocean. While some are predicting a powerful El Ni —o, “others are saying it’s actually going to pack up entirely”.
The reason for this alarming range of predictions is that an El Ni —o can arise due to “random weather variability at very crucial times”. Slight variations in weather elements, like the winds, can trigger off a warming of the Pacific ocean, the primary cause of an El Ni —o. Instead of the normal conditions, where the waters in the eastern part of the ocean (around South America) are colder than those in the western part (towards Australia), “a very small strengthening of the winds in the western Pacific can cause changes in the ocean currents, which then result in a warming on the eastern side of it”.
Scientists generally agree on the importance of the Pacific on weather around the globe. As the world’s hottest ocean, the Pacific provides the main source of energy for the planet’s atmosphere through evaporation. Hence the radical influence of events like El Ni —o in far-flung areas: usually dry areas, like the Chilean coast and California, suddenly experience heavy rainfall; whilst in South Africa, “in an El Ni —o year, more often than not we end up having a drought”.
There is also broad consensus that the last decade and a half have been marked by unusually frequent recurrences of El Ni — o. Some have been exceptionally strong: the El Ni —o experienced in 1982, says Mason, was the strongest the planet has endured for several hundred years.
There are a number of competing theories around why the El Ni —o phenomenon has been dominating the world’s weather in recent years. Some scientists, particularly in the United States, view this prolonged spell of El Ni —o conditions as a climate change attributable to global warming. Since the 1970s, there has been a notable rise in the average temperature of the Pacific – by about half a degree centigrade.
Other scientists would see this warming as only partially responsible for the current spate of El Ni —os. The view of these scientists is that the recurrence of El Ni —o conditions is not evidence of a change in climate, but of a phenomenon known as “interdecadal variability” – a term that describes the swings in weather norms over a longer period of time, but doesn’t constitute climate change.
They point to other unusually long El Ni — -o sequences experienced this century – in the 1910s and again in the 1930s and 1940s – as evidence that the current condition is not that exceptional, and we will soon be returning to “normal” conditions.
So can we expect another El Ni —o this year? The abrupt warming of the Pacific from January until now would suggest that El Ni —o is speedily developing -and in Mason’s personal view, “it’s going to be quite a strong one”.
For us in Southern Africa, we will start noticing it in November, and will feel it most strongly in January at the peak of our rainy season, when we can expect drier than normal conditions.
But Mason also points out a further variable, recently identified by scientists, that could influence how we in Southern Africa experience El Ni —o, should he come visiting. If, through whatever combination of forces, the Indian ocean can remain cold, then we probably won’t have a very serious drought.
Then again, if random happenings can really have such a profound influence over weather, perhaps a bird winging its way south will set off a breeze that brings us months of rain. But we’re not going to know until it happens – and this time, science can’t help us.
For daily updates on El Ni —o, see http://nic.fb4.noaa.gov