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    Parfit, Michael. “Living with Natural Hazards.” (Order issue.)

    Suplee, Curt. “Unlocking the Climate Puzzle.” (Order issue.)

    “El Niño’s Rampage.” Millennium Moments, Order issue.)

    “Do El Niño’s Ripples Extend to Antarctica?” Earth Almanac, (Order issue.)

    “Is the Sea Warming in the Western Pacific?” Geographica, (Order issue.)

    “El Niño Brightens a Desert Landscape.” Geographica, (Order issue.)

    “A Companion for El Niño.” Geographica, (Order issue.)

    Canby, Thomas Y. “El Niño’s Ill Wind.” (Order issue.)

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    Forces of Change: A New View of Nature. 2000.

    Lawrence, Bonnie S., ed. Restless Earth. 1997.

    Agnone, John G., ed. Raging Forces: Earth in Upheaval. 1995.

    Additional Resources

    Bigg, Grant R. The Oceans and Climate. Cambridge University Press, 1996.

    Burroughs, William James. Weather Cycles: Real or Imaginary? Cambridge University Press.

    Diaz, Henry F. and Vera Markgraf. El Niño: Historical and Paleoclimatic Aspects of the Southern Oscillation. Cambridge University Press, 1992.

    Gates, David Murray. Climate Change and its Biological Consequences. Sinauer Associates, 1993.

    Geer, Ira W., ed. Glossary of Weather and Climate, With Related Oceanic and Hydrolic Terms. American Meteorological Society, 1996.

    Graedel, T.E. Atmosphere, Climate, and Change. Scientific American Library, 1995.

    Schneider, Stephen H., ed. Encyclopedia of Climate and Weather. Oxford University Press, 1996.

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  • El Niño/La Niña
    Nature’s Vicious Cycle
    1 | Part 2 | 3

    Over the years, the appearance of La Niña has been less predictable than that of El Niño, and fewer of its effects have been recorded. But both patterns are now far better understood than ever before. That is because the most recent El Niño will be the first to be remembered for more than just a litany of disasters. The 1997-98 El Niño marked the first time in human history that climate scientists were able to predict abnormal flooding and droughts months in advance, allowing time for threatened populations to prepare. The U.S. National Oceanic and Atmospheric Administration (NOAA) first announced a possible El Niño as early as April 1997; Australia and Japan followed a month later. By summer detailed predictions were available for many regions.

    See the progression of El Niño and La Niña through ocean temperatures.



    In northern Peru warnings allowed many farmers and fishermen to make the best of El Niño’s effects. Grass grew on land that is usually barren, and farmers raised cattle. Rice and beans could be planted in areas normally too dry to support them; fishermen were able to plan for shrimp harvests in coastal waters, generally too cold for the shellfish.

    “The potential uses of advance information are almost limitless,” says Michael H. Glantz of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, pointing out how governments and industries around the world can make planning for El Niño and La Niña pay off. For example, Kenyan coffee growers find their product in greater demand when droughts affect coffee harvests in Brazil and Indonesia. Palm oil production in the Philippines typically declines during El Niño, as does the squid catch off the California coast. Countries that anticipate these developments can fill the gaps and prosper.

    At the very least, preparation can save lives. Even in poverty-ridden Peru constructing storm drains and stockpiling emergency supplies saved hundreds of lives during 1997 and ’98. Forewarnings brought timely international aid to such places as Papua New Guinea, where highland populations were threatened with starvation after frost and drought combined to destroy subsistence crops. Many affected areas could prepare for floods and fires, population migration, and the spread of disease.

    There are written records of El Niño’s effects in Peru at least as far back as 1525, and researchers have found geologic evidence of El Niños in Peruvian coastal communities from at least 13,000 years ago. “We know the Inca knew about them,” says Adm. Giampietri Rojas of Peru’s Institute of the Sea. “They built their cities on the tops of hills, and the population kept stores of food in the mountains. If they built on the coast, it was not near rivers. That’s why so many of their dwellings are standing today.” But it was not until about 25 years ago that the rest of the world began to pay attention to El Niño. And after the surprise devastation of 1982-83, climate experts intensified efforts to understand how the process works globally. Governments invested in equipment to monitor the particular conditions in the Pacific that trigger El Niño. Perhaps the most important effort was the development of the TAO (tropical atmosphere/ocean) array of 70 moored buoys to span the equatorial Pacific. Completed in 1994, the TAO buoys are now the world’s premier early-warning system for change in the tropical ocean. They monitor water temperature from the surface down to 1,600 feet [500 meters], as well as winds, air temperature, and relative humidity.

    The data collected by the buoys are transmitted to polar-orbiting satellites and then to NOAA’s Pacific Marine Environmental Laboratory in Seattle. Supplemented with temperature measurements taken by research ships, the data help create a comprehensive portrait of the upper ocean and lower atmosphere.

    Meanwhile the TOPEX/Poseidon satellite, a U.S.-French mission begun in 1992, orbits Earth at a height of 830 miles [1,300 kilometers], measuring sea-surface elevation and relaying information about ocean circulation, including the enormous rhythmic sloshings called Kelvin and Rossby waves that travel back and forth across the entire Pacific.

    Thanks to the TAO buoys, the TOPEX/ Poseidon satellite, and a variety of other tools, climate scientists now have information of unprecedented range and accuracy, which has enabled them to confirm and expand their theories about what occurs both during normal weather patterns and during sea changes that herald the periodic—and inevitable—arrivals of El Niño and La Niña.

    Ground and satellite data show how abnormal El Niño winds send warm air toward California.
    Click to see entire image.

    Weather is so variable that it’s hard to call any situation normal. But in most years climate in the equatorial Pacific is governed by one generally dependable pattern. Sunlight heats the uppermost layer of seawater in the western ocean around Australia and Indonesia, causing huge volumes of hot, moist air to rise thousands of feet and creating a low-pressure system at the ocean’s surface. As the air mass rises and cools, it sheds its water content as rain, contributing to monsoons in the area.

    Now much drier and far aloft, the air heads east, guided by winds in the upper atmosphere, cooling even more and increasing in density as it travels. By the time it reaches the west coast of the Americas, it is cold and heavy enough that it starts to sink, creating a high-pressure system near the water’s surface. The air currents then flow as trade winds back toward Australia and Indonesia. This giant circulatory loop, moving from west to east in the upper air and from east to west at low altitudes, is called the Walker circulation, for Sir Gilbert Walker, the British scientist who studied the process in the 1920s.

    As the trade winds blow westward over the Pacific, they push the warm top layer of the ocean with them, causing the hottest water to pile up around Indonesia, where, because of both wind action and thermal expansion, the sea level is usually about 18 inches [46 centimeters] higher than it is off the west coast of Mexico. All along the eastern Pacific, and especially off Ecuador and Peru, colder subsurface water wells up to replace the sheared-off top layer, bringing up a bevy of nutrients from the deep ocean. That chemical bounty sustains an enormous food web and makes the coastal waters off Peru one of the world’s most prolific fisheries.

    El Niño changes all that. For reasons that scientists still do not comprehend, every few years the trade winds subside or even disappear. The usual air-pressure pattern reverses itself in a phenomenon called the southern oscillation, making barometer readings higher in Australia than they are in the central Pacific. The resulting pattern—known as ENSO, for El Niño/Southern Oscillation—involves only one-fifth of the circumference of the planet. But it transforms weather around the globe.

    Without the trade winds the top layer of the eastern Pacific does not move west. It stays in place, getting hotter and hotter, swelling as it warms. Eventually it hits the threshold for what meteorologists call deep convection—the point at which the steamy surface air blasts into the upper atmosphere. (In some places during 1997-98, sea levels off South America were 10 inches [25 centimeters] above normal and surface temperatures reached almost 86°F [30°C].) When that happens, water in the upper atmosphere condenses and falls as torrential rain on the west coast of the Americas.

    This, in turn, reduces the salinity of the coastal seas, where deepwater upwelling has already declined or stopped. Marine life that customarily thrives off Ecuador and Peru, including economically essential anchovy populations, heads south in search of cooler, richer waters—to the great benefit of fishermen in Chile. Off North America exotic warmwater species suddenly appear farther north. In 1997, apparently for the first time, a fisherman caught a marlin in the ordinarily chilly seas off Washington State. Californians started pulling in bonito and albacore tuna, species normally found only far offshore. Other tuna were netted in the Gulf of Alaska.

    Because El Niño moves the rains that would normally soak the western Pacific toward the Americas, such places as Australia, Indonesia, and India may experience severe drought. According to historical records, 600,000 people died in just one region of India from the epic droughts of the 1789-1793 El Niño.

    In Africa the altered wind, heat, and moisture patterns of El Niño portend drought—generally in the east and extreme south. In particular, cooling of the southwestern Indian Ocean customarily strengthens a high-pressure area that keeps rainfall from reaching the south.

    Meanwhile, back in North America, the jet streams that travel 5 to 8 miles [8 to 13 kilometers] above Earth’s surface shift dramatically. The polar jet stream tends to stay farther north over Canada than usual; as a result, less cold air moves into the upper United States. In fact, northern-tier states saved an estimated five billion dollars in heating costs during the 1997-98 El Niño.

    At the same time upper-level tropical winds reverse themselves, blowing the tops off cyclones forming in the mid-Atlantic and usually reducing the number of hurricanes that strike land in the U.S. by half—from an average of two a year to one or none, according to studies at Colorado State University and Florida State University. One study indicates that El Niño also generally reduces tornadoes in the southern Plains states.

    Return to top | Credits 1 | Part 2 | 3

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