But extreme weather may bring more than wrack and ruin to human societies. New archaeological research suggests that abrupt climate shifts and severe weather events can also create novel opportunities for radical change. Indeed, the earliest civilization in the Americas may owe its beginnings in part to such natural calamities.<\/p>\n
\u201cYou don\u2019t get through climatic or environmental change without changing your culture,\u201d says University of Maine archaeologist Dan Sandweiss. In his studies of ancient societies along the Peruvian coast, Sandweiss has found evidence that one of the world\u2019s most notorious weather patterns\u2014El Ni\u00f1o\u2014may have helped to spur the rise of the New World\u2019s earliest cities, and may also have triggered their fall.<\/p>\n
Sandweiss\u2019s research certainly bears thinking about today, as a new El Ni\u00f1o gathers force in the central and eastern Pacific Ocean. In August, the US National Oceanic and Atmospheric Administration warned that this year\u2019s El Ni\u00f1o could be more devastating than any since 1950, when comprehensive record keeping on the pattern began. And this forecast has prompted widespread warnings about surging coastal storms and disastrous mudslides in regions such as southern California.<\/p>\n
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El Ni\u00f1o, a Spanish phrase meaning \u201cChrist child,\u201d acquired its deceivingly mild moniker in the 19th century, when sailors noticed that the generally cold waters off the coast of Peru and Ecuador turned warm some years around Christmas time. Scientists began to study the phenomenon in earnest starting in the 1920s, and their research now shows that El Ni\u00f1o recurs once or twice every decade with varying intensity. During the winter of 1997 and 1998, for example, weather associated with El Ni\u00f1o took an estimated 24,000 lives and cost more than US $34-billion in damage around the world.<\/p>\n
But all classic El Ni\u00f1os are born from the same conditions. A band of warm water forms in the central Pacific, while a high-pressure system develops to the west and a corresponding low settles along the eastern edge of the ocean.<\/p>\n
In severe years, these changes in the sea and sky set in motion complex interactions with dramatic repercussions around the globe. Grasslands in southeast Australia tend to dry up and catch fire, and packs of Category 3, 4, and 5 typhoons rove the eastern Pacific, threatening Guam and Japan. Already this year, a record-breaking 22 major cyclones have spun across the northern half of the Pacific Ocean. When Hurricane Patricia struck Mexico\u2019s coast on October 23, it was the most powerful storm in terms of barometric pressure recorded in the Western Hemisphere.<\/p>\n
But northern Peru tends to be one of the hardest hit places. The waters off its Pacific coast are home to one of the planet\u2019s most productive fisheries. During an El Ni\u00f1o year, however, the warming waters kill mollusks, seabirds, and sea lions, and force the migration\u2014or interfere with the reproduction\u2014of vast numbers of fish. In a country that relies on its anchovy catch to make fish meal and is the world\u2019s top producer of this commodity, there are fears of serious repercussions.<\/p>\n
A strong El Ni\u00f1o also brings heavy downpours that inundate northern Peru\u2019s coastal deserts and the parched hills that huddle near the foot of the Andes there. This rainfall in turn triggers heavy floods that send debris down the steep stream beds, destroying fields and irrigation works and sweeping away homes and bridges all the way to the ocean\u2019s edge.<\/p>\n
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<\/a>Some researchers predict that this year\u2019s El Ni\u00f1o will be more intense and destructive that the one in the late 90s that brought large landslides to the Peruvian capital, Lima. Photo by Veronica Salem\/El Comercio de Peru\/Newscom<\/p><\/div>\n
The repercussions don\u2019t end with the cessation of rain. In the aftermath of an El Ni\u00f1o in 1578, a Spanish priest watched in horror as remaining crops were \u201ceaten by crickets and locusts and some green worms and yellow ones and other black ones that were bred from the putrefaction of the earth.\u201d Then came mice \u201cthe size of medium rabbits\u201d that gobbled up any scrap of surviving food. And often, along with the threat of famine and swarms of insects, come deadly tropical diseases that attack already weakened human populations.<\/p>\n
Records of El Ni\u00f1os before the arrival of the Spanish in the 16th century are scarce. Peru\u2019s ancient indigenous cultures did not leave any written records that researchers can understand today. And the lake bottoms, trees, and glaciers that typically provide scientists with data on ancient local climates are either in short supply on this stark coast or are difficult to analyze.<\/p>\n
But Sandweiss found a clue to Peru\u2019s ancient climate in 1980 when he took a walk among piles of shells discarded 6,500 years ago near the fishing port of Chimbote. The young archaeologist picked up a few shells that he could not identify and took them to an expert in Lima. She said that they must have come from the warmer Ecuadorian coast 640 kilometers to the north. When he told her their origin, she replied, \u201cImpossible.\u201d The shellfish, she added, couldn\u2019t survive in cold Peruvian waters.<\/p>\n
Sandweiss had stumbled on some of the first physical evidence for a climate regime that predated periodic El Ni\u00f1os. During that earlier regime, waters off the northern coast of Peru were generally warm all year round, and small populations of human hunters and gatherers roamed along the coast. But things began to change some 5,800 years ago. For reasons that remain unclear, Peru\u2019s northern waters became predominantly cold, with aperiodic warming of the seas in winter\u2014the familiar El Ni\u00f1o pattern.<\/p>\n
In the centuries that followed this shift, indigenous people began to build the earliest known monumental structures in South America. One such structure, a mound called Los Morteros, located on the north coast, rose 15 meters in the air, and sprawled over an area the size of three soccer fields. And by 2600 BCE, what is arguably the first city in the Americas took shape at Caral in the nearby Supe Valley. Urban centers soon sprang up across the valley. \u201cThe whole area goes boom,\u201d says Sandweiss.<\/p>\n