What Is El Niño?

When the normally dry Apurímac River near Lima, Peru, swept away just about everything that Carmen owned, she lamented: “There are many of us like this, so many. I’m not the only one.” Farther north, the torrential rains temporarily transformed a section of the coastal Sechura Desert into the second-largest lake in Peru, covering about 1,800 square miles [5,000 sq km]. Elsewhere across the globe, record flooding, intense cyclones, and severe droughts led to famine, pestilence, wildfires, and damage to crops, property, and the environment. What was the cause of all of this? Many point their finger at El Niño, which rose out of the tropical, or equatorial, Pacific Ocean toward the end of 1997 and ran its course for some eight months.

What exactly is El Niño? How does it develop? Why are its effects so widespread? Can its next occurrence be accurately predicted, perhaps reducing its toll on life and property?

It Begins With a Warming of Waters

“El Niño is, strictly speaking, only the warm current of water that appears off Peru every two to seven years,” says Newsweek magazine. For more than a hundred years, sailors along the coast of Peru have noticed such warming. Since these warm currents usually arrive around Christmas, they were named El Niño, the Spanish term for the infant Jesus.

The warming of waters near the coastline of Peru means increased rainfall for that land. The rains cause deserts to blossom and livestock to thrive. When heavy, the rains also bring floods to the region. Moreover, the warm upper layer of seawater prevents the nutrient-filled cooler waters below from welling up. Consequently, many marine creatures and even some birds migrate in search of food. The effects of El Niño are subsequently felt in other places far away from the Peruvian coast. *

Born of Wind and Water

What causes the unusual rise of the ocean temperature near the coastline of Peru? To understand this, consider first the  giant circulatory loop, known as the Walker Circulation, that exists in the atmosphere between the eastern and the western tropical Pacific. * As the sun heats the upper level of waters in the west, near Indonesia and Australia, the hot and humid air rises in the atmosphere, causing a low-pressure system near the water’s surface. The rising air cools down and loses its moisture, bringing rains to the area. The dry air is driven eastward by the winds in the higher atmosphere. As it travels east, the air gets cooler and heavier and starts sinking upon reaching Peru and Ecuador. This causes a high-pressure system near the surface of the ocean. And, at low altitudes, the air currents known as trade winds flow back westward toward Indonesia, thus completing the loop.

How do the trade winds affect the surface temperature of the tropical Pacific? “These winds normally act like breezes in a tiny pond,” says Newsweek, “piling up warm water in the western Pacific so that the sea surface there is as much as two feet [60 cm] higher and 15 degrees Fahrenheit [8°C.] warmer than it is at, say, Ecuador.” In the eastern Pacific, nutrient-filled colder water from below wells up, causing marine life to thrive. Thus, during normal, or non-El Niño, years the sea surface temperature is cooler in the east than in the west.

What changes in the atmosphere bring about an El Niño? “For reasons that scientists still do not comprehend,” states National Geographic, “every few years the trade winds subside or even disappear.” As these winds slacken, the warm water accumulated near Indonesia sloshes back to the east, raising the surface sea temperature in Peru and other places in the east. This movement, in turn, has an effect on the atmospheric system. “A warming of the eastern tropical Pacific Ocean weakens the Walker Circulation and causes the convective zone of heavy rainfall to move eastward, from the western into the central  and eastern tropical Pacific,” states one reference work. Thus, weather patterns along the entire equatorial Pacific are affected.

Like a Boulder in a Stream

El Niño can also alter climate patterns at great distances from the water currents of the tropical Pacific. How? By using the atmospheric circulatory system as an agent. The far-reaching effects of a local disturbance in atmospheric circulation can be likened to the way one boulder in the middle of a stream can cause ripples to form across the entire stream. The dense rain clouds rising above the water of the warm tropical ocean form a boulderlike obstruction in the atmosphere, which affects weather patterns thousands of miles away.

At higher latitudes, El Niño strengthens and displaces the fast-moving, eastward wind currents known as jet streams. The jet streams direct the flow of most storm systems at these latitudes. The strengthening and the shifting of jet streams can also intensify or subdue seasonal weather conditions. For example, El Niño winters are generally milder than normal over parts of the northern United States, whereas they are wetter and colder over some southern states.

How Predictable?

The effects of individual storms can be predicted only as much as several days in advance. Is the same true of the attempts to predict an El Niño? No. Rather than involving short-term weather events, El Niño forecasts involve abnormal climate conditions across large regions for months at a time. And climate researchers have enjoyed a measure of success in El Niño forecasts.

For instance, the forecast for the 1997-98 El Niño was issued in May of 1997—some six months before its rise. Spread across the tropical Pacific now stand 70 anchored buoys that measure wind conditions at the surface and ocean temperatures down to a depth of 1,600 feet [500 m]. When fed into computer models of climate, these data generate weather predictions.

Early warnings of El Niño can indeed help people prepare for the changes that are expected. Since 1983, for example, El Niño forecasts in Peru have encouraged many farmers to raise cattle and plant crops suited for wetter conditions, while fishermen have switched from catching fish to harvesting the shrimp that come with the warmer waters. Yes, accurate forecasting coupled with advance preparation can reduce the human and economic toll of El Niño.

Scientific research into the processes that govern our earth’s climate testifies to the accuracy of the inspired words recorded by King Solomon of ancient Israel some 3,000 years ago. He wrote: “The wind is going to the south, and it is circling around to the north. Round and round it is continually circling, and right back to its circlings the wind is returning.” (Ecclesiastes 1:6) Modern man has learned much about weather patterns from studying wind currents and ocean currents. May we benefit from that knowledge by giving heed to warnings concerning such events as El Niño.

[Footnotes]

[Box on page 27]

EL NIÑO’S TRAIL OF DESTRUCTION

■ 1525: Earliest historical record of an El Niño event in Peru.

■ 1789-93: El Niño was responsible for more than 600,000 deaths in India and caused a severe famine in southern Africa.

■ 1982-83: This event was the cause of more than 2,000 deaths and more than $13 billion in property damage, mainly in tropical regions.

■ 1990-95: Three consecutive events combined to make one of the longest El Niño episodes on record.

■ 1997-98: In spite of the first largely successful regional forecasts of flooding and droughts for an El Niño, about 2,100 lives were lost, and damages amounting to $33 billion were incurred worldwide.

[Diagrams/Maps on page 24, 25]

(For fully formatted text, see publication)

 NORMAL

Walker Circulation pattern

Strong trade winds

Warm ocean water

Cold ocean water

EL NIÑO

Jet streams shift paths

Weak trade winds

Warm water moves east

Warmer or drier than usual

Colder or wetter than usual

[Diagrams/Pictures on page 26]

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EL NIÑO

Red colors on the globe above represent water temperatures much warmer than normal

NORMAL

Warm water piles up in the western Pacific, allowing nutrient-filled colder water to rise in the east

EL NIÑO

Weak trade winds allow warm water to shift back east, blocking cooler waters from surfacing

[Pictures on page 24, 25]

PERU

Flooded Sechura Desert

MEXICO

Hurricane Linda

CALIFORNIA

Mud slides

[Credit Lines]

Pages 24-5 left to right: Fotografía por Beatrice Velarde; Image produced by Laboratory for Atmospheres, NASA Goddard Space Flight Center; FEMA photo by Dave Gatley