The oceans have always been known as major influences on the earth’s climate, but the extent of the seas’ effects wasn’t known until the last few years. In the 1800s, fishermen along the coasts of Ecuador and Peru noted that sometimes the ocean would become much warmer offshore around Christmastime, so they named this thermal change El Niño, which in Spanish means “the Christ child.”
Normally, cold water upwelling from the depths along the coasts makes for good fishing, since it contains nutrients that attract large colonies of anchovies and other types of fish. But during an El Niño event, fish became scarce due to the warmer water, so the fishermen would take time off to maintain their boats, repair their nets, and spend some quality time at home. Most often their break would last from a few weeks to a month, but at other times these warm periods would last much longer than usual, bringing not only warmer sea temperatures but heavy rains as well, and the South American fishing economy suffered as a result.
Winds between 0 degrees (the equator) and 30 degrees latitude generally blow from west to east and are called the Tropical Easterlies, or “trade” winds, since early sailors depended on them to propel their ships. Normally, these prevailing winds blow warm surface water from areas of higher pressure in the eastern Pacific all the way across the ocean, where it piles up in low-pressure areas near western Pacific landmasses such as Indonesia. The surface waters literally do pile up, actually raising the sea level in those areas.
As you’ve learned, water follows wind, so some of the cooler water from the coast of South America is pulled westward; and as it’s dragged along, it warms up from the Sun’s energy. The result is a huge area of warmer water in the western Pacific (containing thirty or forty times more water than all the Great Lakes combined), and cooler water in the eastern regions.
Every few years, the trade winds weaken, and atmospheric pressure starts to rise in the western Pacific while it drops in the eastern Pacific. The trade winds reverse direction, and a giant dome of warm water about 5 feet high, El Niño, begins moving back across the ocean toward South America, where water levels begin to rise. In the western Pacific the levels drop and can actually dip below sea level as the ocean sloshes back toward the east. If you’ve ever tried to carry a pan full of water very far, you’re familiar with the sloshing effect, up one side of the pan and then the other. All the warm water heading east can bring torrential rains and flooding in Peru. Meanwhile on the other side of the ocean, Australia and Indonesia can be experiencing droughts. El Niño rides up over colder water near the South American coast, forcing it downward and choking off the supply of fish that many depend upon for their livelihoods.
When water is sloshing around in a pan it’s oscillating, and when the Pacific sloshes back and forth it’s called the El Niño–Southern Oscillation, or ENSO. El Niños happen about every two to seven years, on average, and every one is different in both its strength and its effects on the global economy.
With the kind of energy El Niño has, it’s not hard to see how these events can cause radical changes in climate across the entire globe. Because the ENSO effect has only been recognized for a relatively brief amount of time, scientists are still building databases that will enable them to try and predict the next one. The Pacific experienced one of the strongest El Niños ever in 1982, and by the time it had faded the following year, nearly 2,000 lives had been lost, hundreds of thousands of people were left homeless, and damage estimates were in the $13 billion range.
The El Niño that began in 1991 lasted until 1995, which is about three to four times longer than average. It also brought the worst drought in southern Africa of the twentieth century, affecting nearly 100 million people.
With friends like El Niño, the earth doesn’t need enemies. Despite all the damage caused by El Niño–generated weather events, these occurrences do have a beneficial side. Hurricanes often form near the western coast of Africa in the summer and travel westward across the Atlantic on the prevailing winds. But in an El Niño year, winds blowing from the west shear off the tops of developing tropical systems, nipping them in the bud before they can get cranked up. Scientists have also found that the increased plant growth caused by heavier-than-average rainfall may trigger a drop in carbon dioxide, a so-called greenhouse gas often implicated in the increase of global warming.
When an El Niño finally loosens its grip on the Pacific, conditions sometimes shift into reverse and a La Niña (the girl child) event begins. Conditions during a La Niña are the opposite of an El Niño: areas that were flooded dry out, and instead of fewer hurricanes, stronger and more frequent storms ply the south Atlantic and the Caribbean.
During a La Niña, also called El Viejo (old man) or the anti–El Niño, high pressure near Tahiti and low pressure over Australia strengthen the trade winds, causing surface waters near Peru to blow out to sea. As they depart, cold water from deep in the ocean rises to take their place, and the Pacific’s surface temperature begins to drop.
La Niñas don’t form quite as often—only about every two to ten years—but their effects on the United States can be just as important as El Niños’. Because the jet stream is diverted into a more serpentine flow during a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler and wetter than normal in the Northwest. La Niña can cause droughts in the American Southwest while bringing much colder weather to the upper Midwestern states. Although it doesn’t usually cause as many problems as El Niño, La Niña’s effects can last much longer.
No two ENSOs are exactly alike, so statistics tell you only the likelihood of a certain condition, not what causes it. That’s where climate modeling—creating a virtual world using simulated weather conditions—comes into play. Data from actual weather analysis is fed in, and analysts can see how close the results are to actual observations.
As the implications of the ENSO have become more obvious, research into the phenomenon and attempts to predict it have gone into overdrive. The 1997 event was the first one ever to be successfully predicted, when the National Oceanic and Atmospheric Administration (NOAA) announced in April of that year the possibility that a strong El Niño would soon form. We now know it to be the strongest ENSO event in recorded history.
Meteorologists use several tools to predict future atmospheric conditions, including El Niños and La Niñas. One is statistical analysis, where scientists examine past weather records to uncover trends that might give them clues to future conditions. Analysts can compile statistics and compare conditions in, say, the eastern Pacific during El Niño years, combine them with statistics on conditions in the western Pacific, and use the results to determine what usually happens in those areas during a warm ENSO event.
In 1997, for the very first time, meteorologists used climate modeling to forecast El Niño, and came up with a prediction that was more accurate than one obtained by statistical analysis. This is an extremely important development for industries, such as agriculture, that depend on the weather. One reason the 1982–1983 El Niño was so devastating to crops is that it wasn’t predicted or even recognized until it was well under way.
After that experience, the Peruvian government undertook a program to predict future ENSO events, realizing their country would be ground zero for every climatic fluctuation. After the system was developed, a forecast for the upcoming growing season was released to the minister of agriculture, indicating that it would be a good year with near-normal rainfall. Sure enough, the forecast was correct, and the government began releasing its predictions each year in November, giving farmers a heads-up on what to plant. If an El Niño is forecast, they can plant water-loving crops like rice, and if La Niña is coming, something more drought-tolerant like cotton can be substituted.
In the United States, the forecasting picture is much rosier than it was in the 1980s. Recognizing that the ENSO knows no boundaries, the United States and France teamed up to launch TOPEX/Poseidon, a satellite system that uses a sophisticated radar altimeter to measure sea levels with an accuracy of within 4 inches. The satellite emits a radar beam that bounces off the ocean surface and returns; by measuring how long it takes for the beam to come back, the distance to the surface and hence the sea level can be determined. Its follow-up program, a satellite called Jason-1, is hoped to be accurate to within less than 1 inch. As sea levels rise in some places and fall in others when an ENSO event is beginning, much earlier warnings will be available to farmers, governments, and the general public, and loss of life and property can be minimized.