Global warming is not causing the El Nino weather phenomenon to become more frequent or intense, an Australian scientist said yesterday.
The current El Nino/Southern Oscillation (ENSO), the strongest ever recorded, has been linked to tornadoes in the United States, crop failures in Africa and droughts in El Salvador and Honduras.
Popular wisdom blames global warming for El Nino's increasing ferocity.
But Dr Richard Grove of the Australian National University in Canberra says the warm current in the Pacific Ocean was causing havoc long before scientists realised that greenhouse gases had destroyed parts of the earth's protective ozone layer.
"Several ENSO events that occurred before 1880 had effects at least as intense and wide-ranging as those associated with the current event," Dr Grove argues in a letter in the science journal Nature.
To back up his claims, he produces archival evidence, particularly of the 1789-93 El Nino, which was one of the most severe.
It caused long droughts in India, Java and south-eastern Australia, reduced the level of Lake Patzcuaro in Mexico and of the Nile in Egypt, caused the most serious famine known to have affected southern Africa before 1862 and may even have changed the course of history.
"This evidence that the 1789-93 ENSO had a strong global impact indicates that it was the most severe on record. "An early precursor of the event may have been an unusually cold winter in Europe in 1787-88, followed by a late and wet spring and summer drought, resulting in the crops failures preceding the French Revolution," he said.
Dr Grove suggests that the failure of the Indian monsoon, which is associated with ENSO, could be an efficient way of forecasting the weather phenomenon.
The early stages of the 1789-93 ENSO were evident in southern India more than a year before it was recorded in the Pacific.
"In peninsular India, every major drought between 1526 and 1900 has been closely associated with the eastern Pacific El Nino, Dr Grove says.