From the enigma of Easter Island to the famines that struck India in the 19th century, the past is throwing up vital pointers for scientists poring over how to combat looming climate change .
Rising global temperatures this century will stress almost every agricultural region of the world, according to the latest report by the UN's Intergovernmental Panel on Climate Change (IPCC).
But for poor tropical nations, the risk is the greatest by far. For them, malnutrition, caused by prolonged spells of drought and flooding, looms as a distant but serious worry.
Experts pondering how to tackle the threat are delving into history, exploring how civilisations of the past, facing similar perils, either coped or were wiped out.
US academic Jared Diamond, author of "Collapse: How Societies Choose to Fail or Succeed," says "ecocide" -- ecological suicide -- plays a greatly under-estimated role in the fall of societies.
He gives the example of Easter Island, the isolated speck of land in the Pacific Ocean, which once had a population estimated to be as many as 20,000 people.
Its civilisation expired in the 18th century in a bloody sunset of internecine warfare and cannibalism after the trees which provided fuel and timber were all cut down.
Prolonged drought wiped out the advanced Mayan civilisation at Tikal, in modern-day Mexico, around a thousand years ago. And in the 15th century, the last Viking settlement in Greenland petered out, a victim of the "Little Ice Age" that brought bitter chill to northern latitudes after several balmy centuries.
"In the worst cases of complete collapse, everybody in the society emigrated or died," Diamond, a professor of geography at University of California, Los Angeles, says in his acclaimed book.
"Obviously, though, this grim trajectory is not one that all past societies followed to completion," adds Diamond. "Different
societies collapsed to different degrees and in somewhat different ways, while many societies didn't collapse at all."
Evan Fraser of the Sustainability Research Institute at the University of Leeds, northern England, says he found a common thread running through the worst famines of recent history.
In research presented at a seminar in Paris last week, Fraser looked at Ireland's Potato Famine of 1845-50, in which around a million people died; at famines that killed around 45 million people in British-ruled India from 1875-1902; and at the 1984-85 famine in Ethiopia that killed around a million.
It might seem nothing links these three events.
Outwardly, Ireland's famine was caused by a blight that destroyed the potato, the staple crop; India's was inflicted by a failure of monsoon rains; and Ethiopia's by a drought.
But, in all three cases, the agro-ecosystems were fragile.
Ireland's potato growers each had tiny strips of land in vast, open fields, making it easy for a blight to rampage through their single crop. In India, forests which could have preserved moisture when water was scarce were massively cut down by the British to make way for tea plantations. In Ethiopia, soil degradation worsened the drought problem.
But environmental abuse was only one factor.
Food shortages were worsened by the destruction of human, social and financial capital, which is vital for keeping agriculture going during a lean spell. And the crisis amplified into full-blown famine in the lack of government support.
Looking at Ethiopia's rainfall pattern between 1960 and 1997, Fraser was struck to discover that the country had, in the early decades, experienced precipitation levels that were just as low as in the year of the drought.
So why did a million die?
The reason, says Fraser, lies in the Soviet-style collectivisation of agricult
ure of the late 1970s. This destroyed Ethiopia's farming communities along with their rich store of knowledge, traditions of self-help and flexible response to crisis.
In Ireland and India, too, coping mechanisms were badly eroded by the time the emergency struck.
The Industrial Revolution drove many of Ireland's farmers into poverty, as they lost non-farming income, such as making linen, to textile mills in Britain. In India, the rural fabric was ripped to pieces as Britain transformed the country into a source of cheap commodities and labour.
When crops failed, the rich and powerful provided almost no help and government support was either inadequate or misdirected, and famine began to bite.
Fraser says the lessons of these disasters can be brought together into an analytical tool to help predict if an agricultural system -- the complex web that includes food growing, trade, storage and distribution, inputs and finance -- is at risk.
"Is the agro-ecosystem resilient? Can farmers adapt? Does the community have assets? Are there institutional safety nets?" asks Fraser.
If "no" is successively the answer to these four questions, the crisis has a progressively deeper impact, he says. In other words, a harvest failure radiates out into the wider economy and then degenerates into a killer famine. Related medicine news :1
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