BY SHANNON BROWNLEE AND LAURA TANGLEY
In normal years, it's rare indeed for a hurricane to reach California. But this is no normal year. Last week Californians and Arizonans held their breath as Hurricane Nora crashed into Mexico's Baja California and raced north. By the time the 88-mile-wide storm hit the coast of the United States its winds had slowed to 54 mile-an-hour gusts; but the storm was still powerful enough to deluge Los Angeles with its first rainfall in a record 219 days, flood homes in Seal Beach when 10-foot waves crashed over a breakwater, and leave three dead in 400 accidents on rain-slicked L.A. and San Diego freeways--three times the usual number for morning rush hour. Flooding in Arizona forced the evacuation of about 1,000 people.
Nora, however, was just a dress rehearsal for the meteorological mayhem that climatologists are predicting will beset the entire globe this winter. The source of the coming chaos is El Nino, a huge mass of warm water in the Pacific Ocean that periodically emerges in a cyclical pattern scientists still do not understand. What they do know is that when El Nino appears it can reach out and rattle weather patterns near and far, spawning hurricanes in the eastern Pacific, flooding in the Gulf States, and drought in Indonesia.
Still growing. Already, this year's El Nino is shaping up to be the biggest in history. The zone of warm water that now sits off Peru is already bigger than the entire continental United States. It stretches more than 6,000 miles, a quarter of the Earth's circumference, and is still growing. Sea-surface temperatures, which are now nearly 9 degrees Fahrenheit above average in parts of the eastern Pacific, have already equaled those measured during the powerful El Nino of 1982-83, which a U.S. government study blamed for 2,000 deaths and $13 billion worth of damage worldwide.
Using the 1982 event as their yardstick, climatologists are predicting that this El Nino will deliver both beneficence and destruction in huge doses. Hurricanes--or a lack thereof--are an early indicator of what's to come. The Atlantic has been eerily calm: Normally the August-to-October storm season brings seven or more hurricanes and tropical storms. But this year has seen only one, Erika. And for only the third time on record, August went by with not a single Atlantic tropical storm.
The Pacific meanwhile has already been hit with 14 storms, and in unusual places. "Hurricanes can exist in water that is about 80 degrees," says Jerry Jarrell, acting director of the National Hurricane Center in Miami. "This year the 80-degree water is about 200 miles north." Storms that normally come to a halt below Baja now have an open door to California.
This year's El Nino has already brought drought to Australia, where cattle ranchers are slaughtering their herds because there is neither water nor fodder. Fires set intentionally to clear rain forests in Indonesia and Malaysia are burning out of control because this year's El Nino has delayed the normal monsoons that would otherwise have doused the flames. The resulting smoke has cut visibility to arm's length in some places, and dangerously low visibility is suspected as a cause in last week's crash of an Indonesian airliner in Sumatra, one of the Indonesian islands most affected by the fires.
Meanwhile, the Atacama Desert in northern Chile, a region that usually gets no rainfall whatsoever--it is so dry and barren that NASA used it this year to test Martian robotic vehicles--has been hit by heavy storms that washed out roads. Last week the World Bank said it anticipated having to bail out developing countries walloped by El Nino to the tune of hundreds of millions of dollars.
Sleeping giant. Climatologists paid little heed to the Pacific Ocean until the El Nino of 1982-83. In the intervening 15 years they have had their view of the world's oceans and weather transformed. In the tropical Pacific, a battalion of buoys now measures winds, currents, and water temperature, transmitting the information by satellite to computers of the National Oceanic and Atmospheric Administration. A scientist--or anybody with a computer, for that matter--can log on to NOAA's Internet site ( HOTLINK !>www.pmel.noaa.gov/toga-tao/el-nino) and find out what was going on in the Pacific yesterday. This mountain of data has established that El Nino drives weather patterns for nearly three quarters of the globe. It is one of the most powerful influences on world climate--second only to the changes in weather brought by the seasons.
El Nino--"the child" in Spanish--was named for the Christ child by Peruvian fishermen, who noticed that the ocean warmed periodically around Christmas time. It is a mild name for a mighty phenomenon. And El Nino is just one phase of a larger cyclical phenomenon--the El Nino Southern Oscillation--that sends sea-surface temperatures in the eastern Pacific climbing above average during El Nino years, and plummeting during the flip side, or La Niña.
For all the public attention to this year's El Nino, says climatologist James O'Brien of Florida State University, La Niña years are actually much nastier to North America, bringing tornadoes to the Midwest, hurricanes to the Atlantic, and drought and forest fires to the Southeast.
Global tango. How can a relatively modest change in ocean temperatures have such far-reaching effects? Imagine the Pacific Ocean as a gigantic basin, with winds blowing across its surface from east to west. Surface waters warmed by the sun are pushed before the winds toward the west, while cool, nutrient-filled water wells up from deep reaches along the eastern margin, near South America. Ordinarily, that causes the Pacific to be a few inches higher on its western end.
During an El Nino, however, the equatorial trade winds slacken. The warm surface water that is normally pushed up against the western side begins to slide eastward.
When this happens a chain reaction follows. Cool, nutrient-filled waters along the west coast of the Americas, which support an abundance of fish and marine life, never make it to the surface, and marine life dies or migrates to other waters. Peruvian fishermen come in with empty nets. As the plume of warm water spreads eastward, the currents of air that rise from warm water in effect suck the trade winds back eastward even more. The rising, moisture-laden air breeds thunderstorms over the eastern Pacific, while the reversal of the normal wind patterns depresses the formation of thunderclouds that ordinarily dump vast quantities of rain on the western Pacific.
A complex change in high-level winds, meanwhile, brings strong air streams 40,000 feet aloft whipping across Central America to the Atlantic and on toward Africa. These winds "shear off the tops of thunderclouds" in the Atlantic before they can coalesce into a hurricane, says Vernon Kousky, a research meteorologist at the National Weather Service's Climate Prediction Center in Camp Springs, Md.
Exactly what triggers an El Nino cycle remains a mystery. But one basic lesson scientists have learned from watching the El Nino cycle is that to understand weather, they must look beyond the sky. It's now clear that the atmosphere is constantly exchanging heat with the world's oceans, and it is this heat that drives the movement of winds and sucks moisture into the atmosphere to make clouds.
But it's a push-me, pull-you affair. Ocean temperatures drive winds; winds drive ocean currents; ocean currents redistribute heat over sea surfaces; and the new pattern of ocean temperatures drives new winds. And so on. The ocean and atmosphere never strike a balance because the ocean moves heat around far more slowly than the atmosphere. "It's like a pas de deux," says NOAA's John Kermond, "except the ocean is doing the waltz and the atmosphere is doing the tango." The net result is that there is really no such thing as a "normal" year; the Pacific Ocean is constantly oscillating between El Nino and La Niña conditions, and the weather is always changing.
Weird effects. El Nino means more than strange weather: It can put rare species at peril, unleash epidemics, and alter ecosystems. These biological effects--and their repercussions for society--are even harder to predict but can account for a huge share of the economic costs that El Nino imposes.
Hurt both by warm water and insufficient nutrients, coral reefs are especially vulnerable. In 1982-83, corals off Costa Rica, Panama, Colombia, and the Galapagos Islands suffered losses ranging from 50 to 97 percent. "It will take decades, if not centuries, for these reefs to fully recover," says Peter Glynn of the University of Miami. This year, corals off Mexico, Costa Rica, and Panama are already dying.
Signs of depressed ocean plant growth from a lack of nutrients are also appearing at California's Monterey Bay Aquarium. Kelp plants at the aquarium that ordinarily thrive in untreated sea water now need Miracle Gro supplements three times a week to stay healthy. In the Galapagos Islands, several albatrosses abandoned their nests in June, a hint that the fish they depend upon already are in short supply.
Such seabirds, as well as marine mammals, suffer some of the most dramatic losses during an El Nino. A powerful 1957-58 event killed some 18 million boobies, cormorants, pelicans, and other diving birds off the coast of Peru. In 1982-83, 85 percent of the country's seabirds died or abandoned their nests, as did virtually all of the 17 million birds living on Christmas Island, in the middle of the Pacific. While suffering less adult mortality, marine mammals often cannot find enough food to raise their young. In 1982-83, 90 percent of Peru's southern fur seal pups perished because their malnourished mothers could not produce enough milk. In California, elephant seals lost more than half of their offspring, mainly because storms and higher sea levels flooded their pupping beaches.
Organisms that transmit human disease, on the other hand, tend to prosper in El Nino years. "In general, extreme weather is bad for human health," says Paul Epstein of Harvard Medical School. Both flooding and drought--because it concentrates water into stagnant pools--improve habitat for mosquitoes that carry malaria, dengue fever, yellow fever, and encephalitis. During the 1982-83 El Nino, Colombia, Peru, India, and Sri Lanka all experienced upsurges in malaria. Storms and flooding also spread waterborne sickness such as dysentery and cholera.
New research shows that even rodent-borne diseases may thrive. Scientists at the University of New Mexico blame the 1992-93 El Nino for a local outbreak of hantavirus: Fueled by heavy rainfall, luxuriant plant growth led to a population explosion of the deer mice that transmit the disease to humans. According to the university's Robert Parmenter, "there's a reasonably good chance" of another outbreak next spring. But this time, he says, health officials are closely monitoring mouse populations as well as teaching people how to steer clear of the rodents.
The brunt of an El Nino's direct economic toll falls on agriculture. El Nino-induced droughts during 1982-83 cost $600 million in Mexico and Central America, $450 million in the Philippines, and $500 million in Indonesia. But southern Africa suffered the most of all: losses of $1 billion and widespread disease and starvation. "For Africa, El Nino means more than sandbags and repairing sea walls," says Michael Glantz of the National Center for Atmospheric Research in Boulder, Colo. "It's a matter of life or death."
With so much riding on accurate forecasting, climatologists are looking forward to using this El Nino to refine their prediction methods. "The societal costs of a big El Nino are pretty grim," says NOAA's Kermond, "but scientifically this is just wickedly exciting." Of the seven supercomputer models that climatologists use to forecast global climate, not one predicted the magnitude of this El Nino. And while researchers have spotted a patch of cooler water in the western Pacific that is the "signal of El Nino's demise," says NOAA's Ants Leetmaa, they don't know yet if an equally severe La Niña will follow.
The data that will come in over the next year and a half should help the modelers do better next time. More accurate and timely forecasts could allow farmers in Peru, for instance, to switch from cotton to water-loving rice in anticipation of wet weather brought by El Nino.
Preparing for El Nino may also serve as a dress rehearsal for the effects of global warming. El Ninos come every three to seven years on average, and most are relatively mild. But something funny may be going on. Between 1991 and 1996, the sea surface was almost continuously warm, and there have been two record-breaking El Ninos in the latter part of this century. Scientists disagree whether this shift in the pattern is evidence that global warming is already here, but some argue that global warming cannot fail to have an effect on the El Nino cycle. Most people will not notice a degree or two change in average temperature, says Steve Zebiak, a climatologist at Columbia University's Lamont-Dougherty Earth Observatory, but a change in the El Nino cycle, and the weather it brings, could be the clearest manifestation of global warming.
With Mike Tharp in Los Angeles, William J. Cook, Betsy Carpenter, and Warren Cohen