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The Oceans In Motion:
El Niño and its Effects

By: Jyotika I. Virmani and Christina Holland
After countless years of quietly going about its business, El Niño has finally gotten public recognition. Planes crashing and ships colliding in Indonesia because of smoke from massive forest fires, hurricanes in Mexico, mud slides and flooding in California, mass destruction of the Amazon rainforest, beaches of dead sea lions in Chile, you get the idea. Now it seems that you can't even go grocery shopping without being affected by El Niño! We have begun to realize how important this climatic phenomenon is, and how it impacts every aspect of life; from increases in the prices of our beloved coffee and chocolate, to increases in diseases; from decreases in gas prices, to a decrease in the number of hurricanes hitting the eastern USA. It's worth your while to learn about El Niño, because the odds are that it will affect you and your students in some way, either now or in the future.
What, you think you've heard enough about El Niño already? We don't think so. In fact, we are dedicating this article to that awesome phenomenon. The Spanish-speaking world knows that el niño means male child. Most of the Spanish-speaking world is Christian. But what do these two facts have to do with our climate? What we now know as El Niño, a warming of sea surface temperatures in the eastern tropical Pacific, occurs every 2-7 years. But once a year, around Christmastime, there is also a smaller warming of these waters off the coast of Peru. Peruvian fishermen were the first to call this annual warming El Niño, in honor of the Christ Child. Catches by Peruvian fishermen decreased during the annual El Niño, not because it was Christmas and they were too busy celebrating, but because the warm surface waters prevented nutrients from deeper in the ocean reaching the surface. The fish would swim away to colder, more nutrient-rich waters. Every few years the fishermen noticed that the warmer waters lasted longer than a couple of months and the warming would start much earlier in the year than normal. This inter-annual warming of the eastern tropical Pacific Ocean is what we now call El Niño. It is much warmer and it covers a larger portion of the Pacific Ocean than the annual warming trend first noted by the fishermen.

Normal Conditions in the Pacific

Before we understand what El Niño is, we need to know the normal conditions in the Pacific Ocean. The water in the west is warm (red region). We call this region the warm pool because it is the warmest part of the entire world's ocean surface. Warm water evaporates, forming clouds, which leads to a lot of rain. So with the warm pool, we get a lot of rainfall in the western tropical Pacific. In contrast to the warm pool region, the water in the eastern Pacific is cold (blue region). Look at the position of the green line in the figure. That's the thermocline - a region in the ocean where water temperature changes rapidly over a short depth. There is colder, nutrient-rich water below the thermocline and warmer, nutrient-depleted water above it. Normally the thermocline is deeper in the western equatorial Pacific than in the eastern equatorial Pacific, so colder water is closer to the surface in the east than in the west. The surface water is colder in the east because the cold water under the thermocline is brought up to the surface by a process known as upwelling (caused by the winds), which happens mainly on the western side of continents. Another reason the water is warmer in the west and colder in the east is directly because of the atmosphere. Winds tend to blow from regions with high atmospheric pressure to areas where the atmospheric pressure is lower. We normally have high pressure over Tahiti, in the eastern side of the Pacific, and low pressure over Darwin, in northern Australia, on the western side of the Pacific. Tropical winds (shown by the yellow arrows in the figure), called the trade winds, blow from the east to the west, pushing the warmest water to the western tropical Pacific. The white arrows show the movement of air in the atmosphere, known as the Walker circulation. In the 1920's, a British meteorologist, Sir Gilbert Walker, discovered that when the pressure is high over Tahiti, it is low over Darwin, and vice versa. Like a see-saw. He called the difference between these two pressures the Southern Oscillation Index.

El Niño Conditions

In an El Niño year, the conditions change. The atmospheric pressure in the western Pacific, over Darwin, gets higher, but over Tahiti it gets lower - Walker's see-saw flips. Because the atmospheric pressure patterns have changed, the trade winds tend to die down or even reverse direction and blow from west to east (the yellow arrows in the figure). Now the trade winds no longer push warmer water to the west, so the warm water is allowed to move eastward, bringing its associated rainfall. This is one reason why the eastern Pacific warms up. The other reason is that the thermocline is now deeper than usual in the eastern Pacific, so the cold water underneath it is deeper. This makes it harder to bring cold, nutrient-rich water to the surface by upwelling.

La Niña Conditions

A third condition in which the Pacific ocean-atmosphere system can exist is the reverse of El Niño. In keeping with the naming convention established by the Peruvian fishermen, scientists have called it La Niña, a female child. It is not as well known as its bigger brother, El Niño, because the changes in climate associated with La Nina are not as severe. During a La Niña event, the high pressure over Tahiti becomes higher than average, and the low pressure over Darwin is lower than average. This leads to extremely strong trade winds blowing from east to west across the tropical Pacific. These winds move the warm pool waters and associated rainfall even further west, and the eastern Pacific gets colder than usual.

El Niños & La Niñas - Past & Present

Evidence of El Niño and La Niña events in the Pacific can be seen in many proxy records, including tree rings, ice cores, and corals. El Niño and La Niña events vary in size, intensity and duration. The last major El Niño (before 1997/98) was the 1982/83 El Niño, which cost 2,000 lives and between $8-$13 billion of damage worldwide. Don't worry, they are not all as severe as that one. In fact, between the 1982/83 and the 1997/98 El Niños, we have had at least two others. Since the 1982/83 El Niño though, scientists have focused on how we can predict these events so that governments can have enough warning to make contingency plans. In 1985, 79 buoys were deployed in the Pacific to continuously monitor the state of the ocean and the atmosphere. Computer prediction models have also been developed to try and predict these events. Currently we can predict an El Niño or La Niña about one year before it reaches maximum intensity (which is usually in November or December). The work done by these scientists paid off this past year. The 1997/98 El Niño event is the largest one this century in terms of its intensity but because we knew so much more about it than in the past, people have had time to prepare. So now that you know all about the El Niño - Southern Oscillation (ENSO) system, as we scientists like to call it, you are probably wondering what is going to happen during the next year? Well, observations from the Pacific show that the 1997/98 El Niño has died down, and computer models predict that we will move into a La Niña phase next. Usually, in a La Niña year there are more hurricanes on the eastern seaboard of the US and possible drought conditions in the mid-western states. Remember, though, that these are still predictions. Mother Nature can throw us a curveball from time to time.
Some Global El Niño Effects Droughts in Australia, eastern Asia and eastern South American countries: Forest fires, including massive destruction of the Amazonian rainforest; Bad crop harvests, including coffee beans and cocoa, leading to increased prices; Famine; Destruction of natural habitats
  • Floods in western South American countries and eastern African countries: Famine; Increases in tropical and infectious diseases such as malaria and cholera; Destruction of natural habitats Changing sea temperatures: Decrease in fish population off South America's western coast leads to massive animal mortality (especially sea lions and birds) and collapse of fishery-dependent economies (for example, Peru); Coral reef bleaching; Increased typhoon activity in the Pacific affecting Central America; Decreased hurricane activity in the Atlantic
      Some El Niño Effects in the United States Floods and mud slides in the western states, especially California
    Wet winters / floods in the southeastern states, especially Gulf states
    Decreased hurricanes in the Gulf states and eastern seaboard states
    Increased hurricanes in the southwestern states, such as Hawaii
    Mild winters in the northeastern states
    Increased diseases in the southern states


Natural Disasters El Nino Oceans From Space Breaking News Real Time Data Red Tide Sea Level Rise Coral Reefs