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Friday, June 01, 2012
How climate change destroyed one of world’s largest civilisationsDaily Times Monitor
LAHORE: Located in present-day Pakistan, the Harappan civilisation fell victim to shifting monsoon patterns, a new study has found. According to The Christian Science Monitor, the mysterious fall of the largest of the world’s earliest urban civilisations nearly 4,000 years ago in what is now India, Pakistan, Nepal and Bangladesh now appears to have a key culprit – ancient climate change, researchers say.
Ancient Egypt and Mesopotamia may be the best known of the first great urban cultures, but the largest was the Indus or Harappan civilisation. The civilisation developed about 5,200 years ago, and slowly disintegrated between 3,900 and 3,000 years ago – populations largely abandoned cities, migrating towards the east.
Nearly a century ago, the CSM states, researchers began discovering numerous remains of Harappan settlements along the Indus River and its tributaries, as well as in a vast desert region at the Indo-Pak border. Evidence was uncovered for sophisticated cities, sea links with Mesopotamia, internal trade routes, arts and crafts, and as-yet un-deciphered writing.
“They had cities ordered into grids, with exquisite plumbing, which was not encountered again until the Romans,” researcher Liviu Giosan, a geologist at Woods Hole Oceanographic Institution in Massachusetts, told LiveScience website.
Like their contemporaries in Egypt and Mesopotamia, the Harappans lived next to rivers. “Until now, speculations abounded about the links between this mysterious ancient culture and its life-giving mighty rivers,” the CSM quoted Giosan as saying. “Our research provides one of the clearest examples of climate change leading to the collapse of an entire civilisation.”
After collecting data on geological history, “we could re-examine what we know about settlements, what crops people were planting and when, and how both agriculture and settlement patterns changed”, said researcher Dorian Fuller, an archaeologist with University College London. “This brought new insights into the process of eastward population shift, the change towards many more small farming communities, and the decline of cities during late Harappan times.”
Some had suggested that the Harappan heartland received its waters from a large glacier-fed Himalayan river, thought by some to be the Sarasvati, a sacred river of Hindu mythology. However, the researchers found that only rivers fed by monsoon rains flowed through the region.
According to the CSM, previous studies suggest the Ghaggar, an intermittent river that flows only during strong monsoons, may best approximate the location of Sarasvati. Archaeological evidence suggested the river, which dissipates into the desert along the dried course of Hakra valley, was home to intensive settlement during Harappan times.
“We think we settled a long controversy about the mythic Sarasvati River,” Giosan said.
Initially, the monsoon-drenched rivers the researchers identified were prone to devastating floods. Over time, monsoons weakened, enabling agriculture and civilisation to flourish along flood-fed riverbanks for nearly 2,000 years.
“The insolation – the solar energy received by the Earth from the sun – varies in cycles, which can impact monsoons,” Giosan said. “In the last 10,000 years, the Northern Hemisphere had the highest insolation from 7,000 to 5,000 years ago, and since then insolation there decreased. All climate on Earth is driven by the sun, and so the monsoons were affected by the lower insolation, decreasing in force. This meant less rain got into continental regions affected by monsoons over time.”
Eventually, these monsoon-based rivers held too little water and dried, making them unfavourable for civilisation.
Eventually, over the course of centuries, Harappans apparently fled along an escape route to the east toward the Ganges basin, where monsoon rains remained reliable, the CSM reports further.
This change would have spelled disaster for the cities of the Indus, which were built on the large surpluses seen during the earlier, wetter era. The dispersal of the population to the east would have meant there was no longer a concentrated workforce to support urbanism.
“Cities collapsed, but smaller agricultural communities were sustainable and flourished,” Fuller said. “Many of the urban arts, such as writing, faded away, but agriculture continued and actually diversified.”
It remains uncertain how monsoons will react to modern climate change. “If we take the devastating floods that caused the largest humanitarian disaster in Pakistan’s history as a sign of increased monsoon activity, than this doesn’t bode well for the region,” Giosan tells the CSM. “The region has the largest irrigation scheme in the world, and all those dams and channels would become obsolete in the face of the large floods an increased monsoon would bring.”
Courtesy www.dailytimes.com.pk