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Understanding El Niño

Understanding El Niño

Education

February 5, 2015

El Niño is a global climate event that occurs at unpredictable intervals every few years, impacting weather around the world. The phenomenon gets its name, which is Spanish for “the Christ child,” from the time of year it occurs, usually in December around Christmas.

An El Niño event occurs when trade winds that normally blow from east to west slow or reverse, and the sea surface temperature along the Equator in the Pacific is at least 0.5 degrees Celsius above normal for three consecutive months. In their normal pattern, trade winds drag warm surface waters across the Pacific and pile them up in the western Pacific, allowing nutrient-rich waters from the deep ocean to move up to the surface along the west coast of South America. This process is called upwelling. The nutrients stimulate the ocean food web creating a bustling fishery off the coast. But an El Niño prevents the colder, nutrient-rich water from reaching the surface.

Marine life may be negatively impacted by El Niño. Without the nutrients provided by upwelling, coastal plankton populations can decline by 90 percent or more. Since plankton are the root of the ocean food web, their decline impacts virtually every species in coastal ecosystems. Filter-feeding fish and other plankton-eating animals may starve or flee to richer habitats, a pattern closely followed by higher-level predators.

There are higher numbers of stranded marine mammals like sea lions and sea otters, as warmer waters cause food scarcity and the stormy seas cause mothers to lose track of their young. El Niño is also highly associated with coral reef bleaching events. The most severe El Niño took place in the winter of 1997 and early 1998 and caused the largest coral bleaching events on record. This is thought to be due to corals’ poor ability to adapt to the higher temperatures that define an El Niño event and is an example of how habitats already stressed by human activity may have difficulty recovering even from natural challenges in the future.

The ongoing drought is a concern for residents of Southern California. Experts predict a 50 to 60 percent chance of moderate El Niño conditions this winter, which may bring much needed rain to California. However, California would need to receive approximately 150 percent of the average rainfall this year to end the drought, and one El Niño year will not make up the difference.

Current climate models are unable to predict what effect global warming might have on El Niño. However, the kinds of extreme events it causes, such as droughts in some regions and stormier weather in others, are predicted to become more intense due to climate change, even outside of El Niño years.

Visitors to the Aquarium can learn more about El Niño in the Ocean Science Center, where a show about the phenomenon plays daily on the National Oceanic and Atmospheric Administration’s Science on a Sphere.

While what happens during El Niño events is well understood, the factors that give rise to them, as well as how their effects may change in the future, are the subject of continuing research. Californians may welcome El Niño, as it can increase our rainfall, but the changes it brings to our ocean also put great stress on ecosystems. By better understanding El Niño’s impacts, we’ll be better able to protect our oceans and prepare for the future.

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