Weather
El Niņo: Far-reaching "fevered sea"
As far back as the 1500s, Peruvian fishermen recognized a phenomenon that spread a "heat wave in the sea" across the Pacific Ocean, killing off the plankton that nourished the marine food chain and driving away the fish. They called this phenomenon El Niņo, Spanish for "the boy child," because its arrival usually coincided with the birthday of the Christ Child. When it appears, about every 3-7 years, El Niņo changes ocean and atmospheric circulation patterns worldwide resulting in the destruction of property, crops, and fisheries. The El Niņo of the winter of 1994-1995 was blamed for torrential rains, floods, and landslides in California, drought and dust storms elsewhere, and even for the balmy January Mainers experienced. This mysterious warming of the Pacific Ocean has far-reaching effects we are just beginning to understand and to predict in forecasts up to a year in advance. Satellites have been the primary research tool scientists have used to track this phenomenon.
El Niņo is a complex interaction between the atmosphere and the ocean. Warming one automatically transfers heat to the other. Higher ocean temperatures increase evaporation, which increases rainfall and changes the atmospheric pressure in the Western Hemisphere. Changes in wind direction cause changes in the circulation patterns and temperature of the ocean, which further disrupt air movements and ocean currents, spinning into an ever more destructive cycle. When an El Niņo occurs, the trade winds, which normally blow from the East to West, die or even reverse, and a warm equatorial countercurrent moves toward South America and California. A wedge of warm water, some 450 feet thick, traps the life-giving cold water in the depths of the sea. When an El Niņo brews in the Pacific, it redirects the jet streams that carry weather around the world. El Niņo shifts heat and moisture eastward from the Western Pacific, drying out Indonesia and Australia while bringing heavy rains to North and South America's Pacific coast.
What are the effects of El Niņo on ocean life? Many fish, such as billfish and tuna, will seek cooler waters, moving into regions where they aren't normally seen. Fish may not return to their normal feeding grounds, disrupting local fisheries, such as the Peruvian anchovy fishery, for many years. The sea birds that feed on the fish, boobies, petrels, cormorants, and gannets, also disappear, destroying another Peruvian industry of guano-collecting for fertilizers. Living things that can't move great distances, like coral and shellfish, will die.
But the most dramatic effect is on the world's weather. Eugene Rasmussen, chief climate analyst of the National Weather Service, said, "When one part of the atmosphere moves, another part feels the kick." One of the worst El Niņos in history, during 1982-83, generated severe drought in Australia (accompanied by dust storms the size of Nebraska), southeast Africa, and Indonesia. While some desert regions had a killing drought, others received 12 feet of rain. Across the Pacific, violent rains, destructive floods, and mudslides battered California, Ecuador and Peru. During 1982-83, the Pacific jet stream moved at twice its normal speed, reducing commercial flying time from Honolulu to Los Angeles by one hour.
Using satellite data, scientists are working to perfect computer models that factor ocean changes that warm surface waters and the resulting atmospheric changes to clouds, convection currents, and wind patterns to predict an El Niņo a year or more in advance. Like short-term weather forecasters, they've had their triumphs and their busts. But scientists and policy makers in Australia, Peru, and Zimbabwe are beginning to use warming and cooling trend predictions in the tropical Pacific to make agricultural projections for their countries. In Zimbabwe, for example, when El Niņo warms the Pacific, maize crops suffer. When the Pacific is cool, Zimbabwe receives ample rain to grow bountiful maize crops. So if an El Niņo is predicted for the next year, farmers can grow drought-resistant maize and the government can store extra grain reserves.
Although the earth may look serene from space, geologic events on land and on the sea floor prove that it is still a dynamic system.
Geologically-active areas associated with volcanoes and earthquakes are usually found along plate boundaries, where geologic plates are colliding, sliding under one another, or pulling apart. Plate tectonics posits that the Earth is divided into many plates, like the pieces of a cracked eggshell, which float along on a 1,800-mile-thick mantle of melted rock or magma. Some plates move up to 4 inches a year. Areas where the plates collide, as along the Pacific Rim (known as the Ring of Fire), experience most of the world's earthquakes, volcanoes, and tsunamis (giant "tidal waves" generated by earthquakes).
Where the plates are pulling apart, as along the mid-oceanic ridges, volcanic material is brought up from deep inside the earth. These eruptions create new land, such as the island of Surtsey near Iceland, or new forms of life around deep-sea vents. As the sea floor spreads apart, hydrothermal fluids up to 400oF (204oC) and lava well up from below. These mineral-rich hot springs, or vents, high in sulfur dioxide, support a new form of life based not on photosynthesis, but on sulfide bacteria. Giant tube worms, crabs, shrimp, large clams, and even fish all seem to thrive on the abundant bacteria found around the "black smokers," the mineral chimneys that spew hydrothermal fluids into the sea water.
Volcanic activity affects not only land and sea, but the atmosphere as well. 1816 was known as the "Year without a Summer" following a powerful eruption of Mt. Tamboura in Indonesia a year earlier. The eruption of Krakatoa in Indonesia in July of 1883 produced similar effects worldwide. This great eruption was heard about 3,000 miles away. It produced sea waves almost 130 feet (40m.) high that drowned 36,000 people on nearby islands. There was a loss of 20-30% of direct solar radiation for three years after the eruption. That explosive eruption injected clouds of debris high into the stratosphere. Large volcanic eruptions like Krakatoa can cause short-term cooling of the climate by ejecting great quantities of dust, ash, carbon dioxide and sulfur dioxide into the atmosphere. Particles of sulfur dioxide in the volcanic dust can reduce the amount of incoming radiation, effectively cooling the upper atmosphere. When the particles of SO2 combine with water vapor, they produce sulfuric acid. Another consequence of some volcanic eruptions is therefore an increase in acid rain.
Brilliant sunsets and cooler summers followed the 1991 eruption of Mt. Pinatubo. The eruption of this Philippine volcano spewed about 15 million metric tons of sulfur dioxide gas into the atmosphere. The resulting aerosol cloud depressed the mean global temperature by some 0.5oC.
