The Fury Of El Nino

By J. Madeleine Nash/Christmas Island With Reporting By Other Bureaus

Only a few months ago, El Nino was starting to look like the most overhyped story of the decade. The periodic warming of Pacific Ocean waters that plays havoc with the world's weather was supposed to be the El Nino of the century--worse even than the great El Nino of 1982-83, which left thousands dead and caused $13 billion in property damage. By last fall, however, El Nino had wreaked only piddling levels of destruction in the U.S., and the public was beginning to see it less as an impending apocalypse than as a gimmick to sell 4-by-4s and generate guaranteed laughs for late-night comedians.

Suddenly, El Nino doesn't seem so funny anymore. Last week one of the most powerful storms on record slammed into California, swamping the coast with 30-ft. waves, drenching the state with torrential rains and blasting it with near hurricane-force winds. Rail lines and major highways were cut by floodwaters up and down the coast, and hundreds of homes were destroyed. By week's end two more storms had struck and at least four people had been swept to their death by mudslides and raging waters. With another severe weather system bearing down on the coast--and ocean temperatures in the Pacific still hovering at an unseasonably high 84[degrees]F--there was no relief in sight.

At the same time--despite a huge storm that set off tornadoes in Florida and dumped snow in the Ohio valley last week, killing at least 22 people--large parts of the eastern and north-central U.S. continued to bask in the warmest winter in years, one that brought cherry blossoms to Washington in the first week of January. That might sound like the opposite of a disaster, but every weather anomaly has its dark side. In a normal year, for example, the winter storm that hit New England and southern Canada in January might have dumped a thick blanket of snow on the region. Instead rain fell on low-lying arctic air and glazed everything in sight with thick layers of ice, knocking out power to 4 million people in one of the worst natural disasters in Canadian history.

Indeed, contrary to the widespread impression--and all those jokes about El No-Show--the El Nino of 1997-98 never really faltered. When you put it all together--forest fires in Indonesia, typhoons in Japan, torrential rains in East Africa, unusually powerful hurricanes in the Pacific, flash floods in Peru and Ecuador, freak snowstorms in Mexico--this El Nino has already unleashed more than its share of epic mayhem. But precisely because its reach is so long and its effects so broadly distributed around the globe, it has been difficult for most people to appreciate the full force of the beast that underlies it all.

The scientists who make it their business to track the world's weather, however, have appreciated it all along. This El Nino may be the most studied weather phenomenon of all time. For months, and in some cases years, meteorologists have been poring over weather maps, running supercomputer simulations, studying coral reefs, tree rings and glacial ice--all to try to understand the dynamics of a pool of warm water in the Pacific.

Their interest is twofold. First they want to better understand El Nino itself--what makes it work, what makes it recur, how it affects human activities. To that end, the National Oceanic and Atmospheric Administration (NOAA) announced last week that it is setting aside $2.1 million to study the impact of the latest flurry of El Nino-related storms.

At the same time, El Nino gives scientists a rare chance to study a phenomenon that transcends the short-term weather forecasts that are the bread and butter of meteorologists. In many ways, El Nino may be a dry run for the kind of large-scale weather effects some scientists predict will accompany the climate changes caused by global warming.

Like global warming, El Nino--or rather, the climate cycle that produces El Nino--does not generate weather per se: rather it alters the context in which weather takes place. The distinction here is a critical one. "Climate," as social scientist Michael Glantz, formerly of the National Center for Atmospheric Research, likes to say, "is what you expect. Weather is what you get."

Sometimes there can be a wide gulf between the two. In Australia, for example, El Nino caused extremely dry conditions that for a while last year had farmers contemplating suicide. But as it turns out, some rain did fall--just in time to rescue the wheat harvest from disaster. Does that mean the drought predictions were wrong? Not at all, says Nicholas Graham, a climate modeler at the University of California at San Diego's Scripps Institution of Oceanography. Think of what El Nino does as the equivalent of rigging a roulette wheel so that it comes up black 40% of the time and red 60% of the time, Graham suggests. "Just because it comes up black once," he says, "you don't conclude the roulette wheel isn't rigged."

In fact, this El Nino has showcased the progress climatologists have made over the past 15 years in understanding the earth's climate machine and the forces that drive it. In 1997, as soon as climate modelers spotted the area of warm water forming in the Pacific, they launched a coordinated effort to predict its effects on various regions of the world. Organized by the new International Research Institute for Climate Prediction--a joint venture of Columbia University's Lamont-Doherty Earth Observatory, the Scripps Institution of Oceanography and NOAA--these efforts have, in the main, been on target.

Scientists predicted, for example, that in western North America the south should be colder and wetter than last winter, while the north would be warmer and drier. That's just what happened: at one point this winter, it was snowing in Guadalajara, Mexico, while thermometers in Saskatchewan registered in the 50s. That doesn't mean the scientists are always right, of course. They can make broad-brush predictions of El Nino's effects without being able to forecast exactly what will happen in any given place. Some of the early prediction scenarios--no snow for the Olympic Winter Games at Nagano and monsoon failure in India--never materialized.

Indeed, this El Nino, like the others that preceded it, has generated as many questions as answers. Why, scientists wonder, does it sometimes torpedo the Indian monsoon and sometimes leave it alone? Is it typical, or very unusual, that as many as four El Ninos have struck over the past seven years? How remarkable is it that two record-breaking El Ninos have occurred within 15 years of each other?

To try and solve these and other puzzles, many scientists have moved beyond their computer models and headed into the field to collect real data. Last week Martin Ralph, a climatologist with NOAA's Environmental Technology Laboratory in Boulder, Colo., spent 25 hours in a P-3 "hurricane hunter" aircraft, flying into the teeth of a Pacific storm to measure temperature, wind and humidity. His goal: to figure out precisely how such storms build, move and interact with the coastline. Along with data from more than a dozen other NOAA experiments, Ralph's information will be fed back into the computer models as a reality check. "We're just learning," he says. "But we've been in the right place at the right time."

By trying to unravel the detailed behavior of El Nino, Ralph and dozens of other researchers are furthering a scientific quest that began in the 1920s, when the British meteorologist Sir Gilbert Walker linked swings in atmospheric pressure over the Pacific to a disastrous failure of the Indian monsoon 50 years earlier. In the 1960s, UCLA meteorologist Jacob Bjerknes suggested that El Nino was governed by the same swings in atmospheric pressure.

The way El Nino works, scientists are now convinced, is that high pressure in the eastern Pacific sends trade winds blowing to the West. Because these winds push water before them like an invisible plow, the sea's surface actually measures about a foot and a half higher around Indonesia and Australia than it does off the coast of Peru. When the pressure drops and trade winds slacken, the water sloshes back downhill, to the east.

This eastward flow is central to the physics that drive El Nino, says Scripps' Nicholas Graham. The sloshing sends waves across the ocean like ripples in a pond. These waves, in turn, push down on the so-called thermocline, a layer of cooler water that normally mingles with the warmer water at the surface. As the thermocline sinks to greater depths, the mixing stops, temperatures at the sea's surface rise, and an El Nino begins.

These ripples can be thousands of miles long, but since they travel 100 ft. or more beneath the surface they're hard to detect directly. So scientists use satellites to pick up the subtle undulations in sea level produced as the ripples pass by. That's how NASA oceanographer Anthony Busalacchi could see early last spring that swarms of undersea waves had started to head out across the Pacific toward the coast of Peru; he followed them as they slammed into the continental shelf, then split, heading sharply south toward Chile and north toward Alaska.

The warm water created by the south-moving ripples created a heat wave that sent residents of Santiago flocking to nearby beaches in the middle of winter, while the north-moving waves triggered a sharp rise in ocean temperatures off California and Washington State, delighting sportfishermen by attracting tropical species like marlin to usually frigid waters.

These subsurface waves explain more than the origin and propagation of El Ninos. They also explain how El Ninos end. When the waves first hit the South American coast, some reflect back, like sound bouncing off a wall. When the reflected waves reach Asia, they rebound again. But this double bounce inverts their effect: instead of depressing the thermocline, these twice-reflected waves now lift it up. Cool water dilutes the warmer liquid at the surface, causing a temperature drop in the eastern Pacific known, aptly enough, as La Nina. Thus, observes Ants Leetmaa, director of the National Climate Prediction Center, "each El Nino contains the seeds of its own destruction."

La Nina can bring its own set of weather headaches: a drier, hotter southern tier and a wetter, colder north. "Like a pendulum that goes back and forth, El Nino is one side of the extreme and La Nina is the other," says Scripps' Lisa Goddard. Although the magnitude of an El Nino doesn't necessarily determine the size of the subsequent La Nina, some climatologists are already saying that if you think this El Nino was bad, wait until you see his sister.

How long this boom-and-bust cycle has been operating, no one really knows. Finding out might seem to be a hopeless task, considering that the phenomenon was discovered only about a century ago by Peruvian fishermen. (It was they who called it El Nino, the Spanish name for the Christ child whose December birthday marks its peak.) But last fall, Columbia University oceanographer Richard Fairbanks was floating in the equatorial Pacific gathering data that could tell researchers about El Ninos going back thousands of years. Working aboard the research vessel Moana Wave, Fairbanks spent weeks at El Nino's very epicenter, a patch of ocean near Christmas Island. Using a powerful oil drill, he and his colleagues repeatedly bored into ancient reef beds buried beneath the sea floor, pulling up chunks of coral as white as sun-bleached bone.

Corals, it turns out, are like miniature thermometers and rain gauges. When water temperatures rise, these small creatures incorporate less strontium into their skeletons than they do under cooler conditions. Their oxygen content, meanwhile, records salinity swings, which in turn can be used to estimate rainfall. And warm temperatures and heavy rainfall--here, at least--are the telltale markers of El Nino.

Corals are not the only recorders of climate history. Jay Noller, for example, a geomorphologist from Vanderbilt University, has been studying ancient sediments from Peru's northern desert, which is among the dryest spots on earth--except during El Nino years. Then and only then, torrential rains from a succession of storms compact surface dust into a layer of fine, red soil. From the age of the soils he has examined so far, Noller concludes that the El Nino cycle has been operating for at least 2 million years, and probably much longer.

But that doesn't mean it has always oscillated, as it does today, roughly every two to seven years. Fairbanks, for one, thinks the present pattern may have switched on between 14,000 and 9,000 years ago, when rising sea levels swamped a landmass that included present-day Australia and Indonesia. Such a continent could have stabilized atmospheric pressure, keeping El Ninos from ever getting started. Whether this hypothesis is correct, no one yet knows. But the bits of coral Fairbanks and his team wrested from the submerged reefs around Christmas Island nicely bracket the period in question.

Trees too can preserve evidence of long-past climate patterns. David Stahle of the University of Arkansas Tree Ring Lab recently presented data derived from teaks in Java and firs in Mexico and the American Southwest that date back to 1706. The thicker the trees' growth rings, the more rain fell that year. According to Stahle, "it looks like a substantial shift occurred after 1880." After that date, the rainfall patterns typical of El Nino start to recur on average every 4.9 years instead of every 7.5, while patterns typical of La Nina show up at 4.2-year intervals versus once a decade.

An even longer-term perspective comes from paleogeologist Lonnie Thompson of Ohio State University, who specializes in extracting climate histories from mountain ice. Like trees and corals, ice grows in distinct layers whose thickness depends on the snowfall in a given year. Drilling into the Quelccaya ice cap in the Andes of Peru, Thompson has detected the short-term precipitation swings typical of El Nino and La Nina.

No one of these climate records is perfect. Storms in the Andes may hit or miss a particular location regardless of the overall weather pattern. Trees provide more comprehensive geographical coverage, but not always in the right locations. The palm trees that grow on tropical islands, for example, do not have rings that are useful for dating.

Out of all of this information, though, a crude picture begins to emerge. It appears the El Nino cycle is considerably more variable than scientists previously imagined, subject to protean swings of mood that last anywhere from decades to hundreds or even thousands of years. To account for this eccentric behavior, many scientists invoke the science of chaos, which says slight differences now--a barely perceptible increase in wind speed, for example--can lead to a dramatic change down the road. According to this scenario, the El Nino cycle resembles a chaotic pendulum whose swings never retrace the same path. Yet there is also a rhythm to the swings, like a jazzman's improvisations, endlessly circling a central theme. Chaos routinely pops up, in fact, when Lamont-Doherty climate modelers Stephen Zebiak and Mark Cane run computer simulations of the El Nino cycle. All the virtual El Ninos resemble one another, says Zebiak, but out of thousands of simulations, no two evolve in precisely the same way.

Just to make things even more complicated, it now seems that some of the variations in El Nino cycles come from outside, imposed by other components of the world's intricately interconnected climate system. "We've been treating El Nino as a purely tropical problem, but what if it isn't?" asks Princeton University Oceanographer George Philander. What if some external force--a wind-driven current, say, that sweeps warm water down from the north--were to make it easier for the next El Nino to start?

Such a current, Philander thinks, could explain the unusual spate of El Ninos that marked the first part of this decade. Think of the cycle as one of the strings on the climate's violin, he suggests. "When something changes the tension on the string, the frequency of the vibration also changes."

External forces may also help explain why El Nino has a different impact on the weather from one cycle to the next. Recently, for example, Ed Cook of Lamont-Doherty and Julie Cole of the University of Colorado used tree rings from hundreds of sites to see how El Nino affected North America in the past. Before 1920, they found, El Nino appears to have affected a much larger region of the U.S. than it does today, channeling winter rain and snow all the way up into the Great Lakes and Great Plains. Afterward, however, its sphere of influence retreated to northern Mexico and the American Southwest. Why the shift? It may be, Cole suggests, that El Nino is overlaid on a different climate cycle that is even more important.

One prime suspect is something known as the Pacific decadal oscillation. Since 1977, say researchers from the University of Washington, it has been locked into a mode that has made winters in the Pacific Northwest warm and dry, just as El Nino tends to do. But according to climatologist Nathan Mantua, the Pacific oscillation was in a different phase between 1947 and 1976, and as a result winters in Washington State were cold and rainy.

Yet another player in the El Nino drama is a cycle in the tropical Atlantic that involves a flip-flop between twin pools of water--one warm, one cool--that sit on opposite sides of the equator. Depending on the configuration, farmers in northeastern Brazil could either suffer greatly at the hands of El Nino or feel very little at all.

And then there's the North Atlantic oscillation, which makes El Nino's effect on the eastern U.S. as unpredictable as its influence over Brazil. This climate system, says Gerry Bell of the Climate Prediction Center, changes the position of the jet stream over the ocean. Until recently, the North Atlantic oscillation, which strongly influences Europe's weather as well, was considered to be primarily a manifestation of the atmosphere. But researcher Michael McCartney of the Woods Hole Oceanographic Institution thinks it too is heavily influenced by the sea--in this case by an ocean gyre, a surface current that follows a sweeping circular route. This gyre, he believes, affects the atmosphere by shuttling parcels of warm and cold water between the tropics and northern latitudes.

Each of these phenomena can boost or curb the effects of El Nino. But do they influence each other at a deeper level? Does El Nino trigger any of these other cycles? Is it triggered by them? To find out, Fairbanks turned to the Indian Ocean, where sea-surface temperatures, it turns out, rise and fall in response to both the monsoonal cycle and the El Nino cycle.

And as he and his colleagues reported in a recent issue of the journal Science, a 150-year-old coral from the Seychelles Islands perfectly preserves both sets of fluctuations. One pattern tracks the El Nino fluctuations, swinging back and forth every few years; the other rises and falls on a 12-year schedule that closely follows India's official monsoon-rainfall index.

What stands out in the data is an unusually sharp rise in sea-surface temperatures in 1877, the very year that a strong El Nino coincided with the greatest failure of the monsoon in recent times. "The way I think of it," says Fairbanks, "is as an orchestra. Sometimes the monsoon and El Nino play together, and sometimes they play apart. But where's the conductor?"

Where indeed? While all these climate cycles seem to involve both atmosphere and oceans, more and more scientists are abandoning their long-held belief that the former runs the show. The atmosphere is fickle, they observe. Storms form, then quickly dissipate, so whatever information they contain about the conditions that created them is quickly lost. By contrast, ocean gyres take anywhere from 10 to 20 years to complete a single journey, making them perfect vehicles for transmitting messages into the future. With the exception of the tropical Pacific, unfortunately, the oceans are even less well monitored than the surface of the moon. The changes they undergo, moreover, exceed any individual scientist's lifetime.

That's why corals and tree rings and ice cores are so important. They are like a tape recording of the various instruments in the climate orchestra, ranging from El Nino's high-frequency violin to the deeper cello- and basslike tones struck by longer-term cycles. By studying the hidden rhythms in these signals, scientists may finally be able to see how the parts fit together, sometimes harmonizing, sometimes clashing.

Over the next few years, Fairbanks hopes, he and others may shed light not only on El Nino's past but on its future as well. For if, as many experts expect, the atmosphere warms owing to the buildup of greenhouse gases, the El Nino cycle could very well change. But how? Would it speed up, slow down or stop entirely?

Given the present state of knowledge, no one can tell. The more scientists learn about the earth's climate system, the more complex and interconnected it seems, and the harder it is to unravel. That does nothing to diminish the tremendous advances that have occurred over the past decade. In fact, it is only because they have learned so much that scientists are finally ready to tackle the questions that the current El Nino has so eloquently framed--questions that may still be formidable, but perhaps no longer quite so intractable.

--With reporting by other bureaus