What is the El Niño effect?

El Niño is part of a natural system that involves the interaction of the atmosphere and ocean to produce variations is sea surface temperatures (SST’s) in the tropical Pacific Ocean. This natural system is known as the ENSO system, short for El Niño Southern Oscillation, and comprises of El Niño warming events and La Niña cooling events of SST’s.

The system occurs on a 2-7 year cycle and is driven by a certain group of winds in the Pacific Ocean known as trade winds that typically blow fperom east to west. During El Niño years these winds weaken, meaning the movement of warmer seawater towards the western Pacific is reduced. Consequently, warmer waters rise in eastern areas of the Pacific near the west coast of South America. The process can be visualised most effectively via this video courtesy of the BBC:

As is mentioned in the video, this phenomenon impacts upon regional climates all over the world. The video mentioned that there is evidence to suggest that the El Niño phenomenon was partially linked to the severe winter experienced in the UK in 2009/10. This is because the temperature changes brought about by El Niño are thought to possibly influence the behaviour of one of the major atmospheric air flows that dictates the weather we get here in the UK. This stream is known as the jet stream, and there is on-going research into how the El Niño phenomenon impacts the level of sinuosity (bendiness) of the jet stream.

Given the abnormally mild and wet winter we have just experienced in the UK this past winter, it will be interesting to see what results this research brings, and to what extent the El Niño phenomenon can influence global weather. This year’s El Niño is already thought to be one of, if not the strongest on record, comparable to the very strong El Niño witnessed in 1998. Consequently, it is thought that the strong El Niño did contribute partially to 2015 becoming the hottest year on record, surpassing 2014.

The ENSO system is incredibly complex and many of the physical models designed to predict its future dynamics require much improvement. The phenomenon makes assessing global climate change slightly more difficult in terms of anthropogenic, or human caused global warming, because the temperature anomaly it produces can impact average global temperatures. How the system will change in a changing climate is also relatively unknown because of the severe complexity and variation of the system. What is for certain is that the ENSO system will continue to cycle for the foreseeable future, and understanding its functioning more accurately will provide us with a greater understanding of how the climate system works and inter-functions.

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Chris Holdsworth 8 Articles
My writing interests spawn from my studies in Earth Sciences. The natural world fascinates and amazes me, but engaging and involving others in science is my greatest passion because of the ever-growing need for interest and understanding of the natural world.

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