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 back
                  only 2,000 years, even though scattered evidence of much older El Ninos
                  existed.

                  But the results of a new study from a lake high in the Ecuadorean Andes put
                  scientists on a path toward better predicting what El Nino will do in the
                  future.

                  "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 in
                  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 flood
                  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
                  interview.

                  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 of El
                  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
                  emissions.

                  Extreme flooding and drought conditions are the most well-known results of
                  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 of
                  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
                  coastal Peru.

                  "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.