Study of El Niño in history reveals clues for future
	Dry argument: This 1792 drawing of Sydney Cove shows trees growing in the dried-up Tank Stream (centre). It is the only time in recorded history that the stream was dry and was believed to have been caused by one of history's worst El Niños.
By Julian Lee An increase in the frequency and intensity of recent El Niño events has led some scientists to blame global warming but, after taking a longer look at history an ANU researcher has another explanation. Dr Richard Grove of the History Program and Global Environmental History Unit in RSSS, said most previous research has focussed only on mechanisms in the Pacific Ocean, but he believes El Niño events have a more complicated and lengthy build up. "The research shows there seems to be a global mechanism for the strongest El Niños, and that monsoons may be used to predict when they will occur," said Dr Grove, who helps to coordinate the work of environmental historians in the university and produce an international journal, Environment and History,. In an article published in Nature last month, he explained that the biggest recorded El Niños started with a weak phase of the North Atlantic Oscillation - the northern hemisphere equivalent of El Niño. "A weak phase of the Atlantic Oscillation leads to very cold weather in Europe, then high pressure and cold air over inner Asia which blocks the Southeast Asian monsoon," Dr Grove said. With the Southeast Asian monsoons blocked, a rise in sea surface temperatures in the Indian and Pacific Oceans soon follows, causing an El Niño, he said. "There is a direct correlation in most El Niño events between the North Atlantic Oscillation, the Asian monsoon, and the Indian and Pacific Ocean El Niños," he said. Having discovered this correlation, Dr Grove believes monsoon failures can be used to predict El Niño events. "Very often with a failure in the Asian monsoon, and always with the failure of the Indian monsoon, there will be a strong El Niño at the same time or soon after," Dr Grove said. The worst consequences of a global El Niño of the type Dr Grove has described are felt in South-Asia and Southern Africa. "At least 90 million people may have died in El Niño associated famines in India between 1200AD and 1900AD," he said. These events have been so severe that Dr Grove believes they have had a hand in shaping history. While the 1982­1983 El Niño-induced drought affected the livelihoods of many Australians, the 1789­1793 El Niño was very much stronger, he said. "The colonisation of Australia was almost put to an end when the Tank stream running into Sydney harbour dried up, the only time in recorded history that this has happened," Dr Grove said. Elsewhere, El Niño may have caused some of the worst harvests ever known in French history - precipitating the French revolution, he said. "Similar El Niños in 2200 BC and 1200 BC wiped out early empires such as those of the Hittites and Akkadians, and gave rise to the Trojan wars and the kind of piracy recorded in the Iliad and the Odyssey. "The danger of a similar repeat event is still there," Dr Grove said. He added that scientists now recognise the fundamental value of history and classics in understanding environmental history - an increasingly important subject in present day environmental crises.