WASHINGTON (Reuters) -- Sediment samples from a lake high in the
Ecuadorean Andes show that the warm-water migration known as El Nino
has been playing havoc with the world's weather for at least 15,000 years,
researchers said on Thursday.
A team digging in the Andes mountains has found a continuous geological
record of El Nino weather events dating back 15,000 years, in what they
said was an important step in understanding the phenomena that can unhinge
weather conditions worldwide.
El Nino is the common name for a regular eastward migration of warm water
from the tropical western Pacific Ocean. First noticed by Peruvian and
Ecuadorean fisherman, it is blamed for setting off weather patterns that cause
flooding, droughts and storms across the globe.
Previously, scientists had been able to chart the pesky weather pattern
only 2,000 years, even though scattered evidence of much older El Ninos
But the results of a new study from a lake high in the Ecuadorean Andes
scientists on a path toward better predicting what El Nino will do in the
"It gets us closer to understanding what might cause the changes in the
frequency of El Nino," said Don Rodbell, a geologist at Union College in
New York, who led the study.
"We really need to know what has caused El Nino to change its frequency
the past before we can begin to say what it will do in the future," he added.
The team of researchers cored the bottom of Laguna Pallcacocha and found
that flood deposit marks from the 30-foot long (10 meter) sediment sample
matched known El Ninos from the past 200 years.
Using chemical analysis, the researchers then looked at the rest of the
deposits, which are a tell-tale mark of an El Nino event, and charted the
weather pattern's frequency rate back 15,000 years.
"In the lake sediments we could see layers of flood deposits that were
washed in during what we think were El Ninos," Rodbell said in a telephone
Writing in the journal Science, researchers said the chemical dating also
showed El Ninos have become much more frequent in the last 5,000 years,
occurring about every two to eight years instead of every 15 to 35 years
when the Earth was hotter.
"What we found in the record for the last 5,000 years is the frequency
Ninos have changed a lot," he said. "Events were separated by greater and
greater amounts of time as you go farther back."
Rodbell said it was unclear why El Nino events increased as the Earth
cooled but an answer might offer clues concerning how the weather pattern
will react to present day global warming caused by greenhouse gas
Extreme flooding and drought conditions are the most well-known results
El Nino events, but some ancient civilizations actually benefited from the
weather changes, said Daniel Sandweiss, an archaeologist at the University
of Maine in Orono.
In a related article in the journal Science, Sandweiss wrote that the onset
El Nino rains between 5,000 and 8,000 years ago gave a boost to crop
production and may have helped spur ancient temple building in parts of
"Although we associate El Nino with disaster in Peru, it usually brings
benefits to the central coast," he wrote. "The onset of El Nino and the
associate flourishing of resources may therefore have facilitated the cultural
transition evidenced by the temple mounds."
But while plants bloomed on the Peruvian coast, parts of Brazil faced severe
drought, Rodbell said. And the damage from any El Nino is usually far
greater than any positive results.
"I think there is no question the costs outweigh the benefits," Rodbell said.
Copyright 1999 Reuters.