Black Swans And The Death Of Empires
(Inside Science) -- If El Niño, the periodic Pacific weather pattern, returns this winter, the increased rain could save California from its current severe drought. But while El Niño can rescue areas from drought, it can destroy entire civilizations, as scientists are now discovering.
Everything from the great influenza pandemic of 1918, which killed 50 million people, to the fall of the Mayan and Inca empires can be linked to El Niño, and the evidence is in the most unlikely of places -- tropical glaciers.
For years, Lonnie G. Thompson, a paleoclimatologist at The Ohio State University in Columbus, has been drawing ice core samples from glaciers atop the Andes Mountains in Peru and from the Himalayas in Tibet. The samples, still frozen and shipped to Columbus, show wet and dry periods, including those associated with El Niño events going back thousands of years.
In the early 1980s, Thompson became one of the first scientists to note global warming. His ice core collection is considered some of the strongest evidence of warming, and to most scientists, proved the climate is changing dramatically.
That there are such things as tropical glaciers seems counter-intuitive but huge mountain chains like the Himalayas and the Andes are in the tropics and are high enough, their peaks cold enough, to create ice fields and glaciers. The glaciers in Peru are the largest.
El Niño are large scale atmospheric oscillations responding to sea surface temperatures in the western Pacific. An increase in surface temperature influences the temperature in the atmosphere and the flow of the trade winds. Every several years, it'begins a feedback loop that eventually makes its way to the Americas and ends up influencing the world’s climate, according to David Unger, a meteorologist at the National Oceanic and Atmospheric Administration's Climate Prediction Center in College Park, Maryland.
Some places get warmer and wetter; others get colder and drier.
Much of Thompson's work is based on exploration of the Peruvian glaciers at Quelccaya, and analyzing thousands of ice cores made from ice formed up to 1800 years ago. The fields he explored were less than 60 miles from Cusco, the capital of the once great Inca Empire.
The ice, along with archaeological studies, showed that people moved from the highlands to the coast and back as El Niño altered the climate. While it is unlikely El Niño events were the only cause of the disasters that destroyed the Inca, the alterations in the weather and its effect on water resources and agriculture, Thompson believes, were crucial.
The same appears true of other indigenous people in the Americas, including the Moche.
That sounds plausible to Unger. The findings have been corroborated by radiocarbon dating.
"Central America tends to be one of the most sensitive areas to El Niño," Unger said.
"In climate, I think it's remarkable that … in ice fields on both sides of the Pacific, there are recording of major droughts in written histories in terms of major social unrest," Thompson said this week to a meeting of the Council for the Advancement of Science Writing in Columbus, Ohio.
The ice records are what scientists call "black swans," rare but inevitable, dramatic events.
El Niño events usually last only one year, Unger said, although an opposite oscillation, called La Niña, can last two or three. El Niño events have been running every four years. Thompson is not the only scientist to link black swan events to El Niño.
The connection to the flu pandemic goes back to 2010 when Benjamin Giese at Texas A&M University in College Station reported that a review of centuries of El Niño records showed that the 1918-1919 occurrence was unique. It was strong in the central Pacific but oddly milder along the coast of the Americas.
The location, he wrote, triggered a severe drought in India when the monsoons failed, and 18 million Indians died. The flu coincided with the public health emergency there and spread into Europe and America.
Thompson pointed out that 1918 was not just the year of the flu but the end of World War I and several political upheavals, including the Russian Revolution.
In 1781, the monsoon also failed and 600,000 Indians starved to death. The same year, black swan events devastated Australia, Egypt, Mexico and the Caribbean, Thompson said.
An El Niño accompanied the Black Death, the plague that wiped out 200 million people and perhaps half the population of Europe around 1346. That same year, the Yuan dynasty in China, where the plague probably originated, was overthrown by the Ming, one of the most important events in Chinese history, he said. The ice documented a 30-year drought.
As to California, scientists predict there is about a 60 percent chance an El Niño this winter would end the drought. Earlier in the year, it seemed like a slam dunk, scientists said, but it is not turning out as a classic El Niño, according to Unger, so the odds are lower.
Meanwhile, the tropical glaciers are dying just as quickly as those in Greenland and Antarctica, he said. For example, Thompson predicts that a glacier in New Guinea will be gone by 2017.