̽��ֱ�� of Cambridge - Monsoon

Decline of Bronze Age ‘megacities’ linked to climate change

lw355 — Thu, 27 Feb 2014 12:57:09 +0000

Scientists have demonstrated that an abrupt weakening of the summer monsoon affected northwest India 4,100 years ago. ̽��ֱ��resulting drought coincided with the beginning of the decline of the metropolis-building Indus Civilisation, which spanned present-day Pakistan and India, suggesting that climate change could be why many of the major cities of the civilisation were abandoned.

̽��ֱ��research, reported this week in the journal Geology, involved the collection of snail shells preserved in the sediments of an ancient lake bed. By analysing the oxygen isotopes in the shells, the scientists were able to tell how much rain fell in the lake where the snails lived thousands of years ago.

̽��ֱ��results shed light on a mystery surrounding why the major cities of the Indus Civilisation were abandoned. Climate change had been suggested as a possible reason for this transformation before but, until now, there has been no direct evidence for climate change in the region where Indus settlements were located.

Moreover, the finding now links the decline of the Indus cities to a documented global scale climate event and its impact on the Old Kingdom in Egypt, the Early Bronze Age civilisations of Greece and Crete, and the Akkadian Empire in Mesopotamia, whose decline has previously been linked to abrupt climate change.

“We think that we now have a really strong indication that a major climate event occurred in the area where a large number of Indus settlements were situated,” said Professor David Hodell, from Cambridge’s Department of Earth Sciences. “Taken together with other evidence from Meghalaya in northeast India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.”

Hodell together with ̽��ֱ�� of Cambridge archaeologist Dr Cameron Petrie and Gates scholar Dr Yama Dixit collected Melanoides tuberculata snail shells from the sediments of the ancient lake Kotla Dahar in Haryana, India. “As today, the major source of water into the lake throughout the Holocene is likely to have been the summer monsoon,” said Dixit. “But we have observed that there was an abrupt change, when the amount of evaporation from the lake exceeded the rainfall – indicative of a drought.”

At this time large parts of modern Pakistan and much of western India was home to South Asia’s great Bronze Age urban society. As Petrie explained: “ ̽��ֱ��major cities of the Indus civilisation flourished in the mid-late 3rd and early 2nd millennium BC. Large proportions of the population lived in villages, but many people also lived in ‘megacities’ that were 80 hectares or more in size – roughly the size of 100 football pitches. They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East. But, by the mid 2nd millennium BC, all of the great urban centres had dramatically reduced in size or been abandoned.”

Many possible causes have been suggested, including the claim that major glacier-fed rivers changed their course, dramatically affecting the water supply and the reliant agriculture. It has also been suggested that an increasing population level caused problems, there was invasion and conflict, or that climate change caused a drought that large cities could not withstand long-term.

“We know that there was a clear shift away from large populations living in megacities,” said Petrie. “But precisely what happened to the Indus Civilisation has remained a mystery. It is unlikely that there was a single cause, but a climate change event would have induced a whole host of knock-on effects.

“We have lacked well-dated local climate data, as well as dates for when perennial water flowed and stopped in a number of now abandoned river channels, and an understanding of the spatial and temporal relationships between settlements and their environmental contexts. A lot of the archaeological debate has really been well-argued speculation.”

̽��ֱ��new data, collected with funding from the Natural Environment Research Council, show a decreased summer monsoon rainfall at the same time that archaeological records and radiocarbon dates suggest the beginning of the Indus de-urbanisation. From 6,500 to 5,800 years ago, a deep fresh-water lake existed at Kotla Dahar. ̽��ֱ��deep lake transformed to a shallow lake after 5,800 years ago, indicating a weakening of the Indian summer monsoon. But an abrupt monsoon weakening occurred 4,100 years ago for 200 years and the lake became ephemeral after this time.

Until now, the suggestion that climate change might have had an impact on the Indus Civilisation was based on data showing a lessening of the monsoon in Oman and the Arabian Sea, which are both located at a considerable distance from Indus Civilisation settlements and at least partly affected by different weather systems.

Hodell and Dixit used isotope geochemical analysis of shells as a proxy for tracing the climate history of the region. Oxygen exists in two forms – the lighter ¹⁶O and a heavier ¹⁸O variant. When water evaporates from a closed lake (one that is fed by rainfall and rivers but has no outflow), molecules containing the lighter isotope evaporate at a faster rate than those containing the heavier isotopes; at times of drought, when the evaporation exceeds rainfall, there is a net increase in the ratio of ¹⁸O to ¹⁶O of the water. Organisms living in the lake record this ratio when they incorporate oxygen into the calcium carbonate (CaCO3) of their shells, and can therefore be used, in conjunction with radiocarbon dating, to reconstruct the climate of the region thousands of years ago.

Speculating on the effect lessening rainfall would have had on the Indus Civilisation, Petrie said: “Archaeological records suggest they were masters of many trades. They used elaborate techniques to produce a range of extremely impressive craft products using materials like steatite, carnelian and gold, and this material was widely distributed within South Asia, but also internationally. Each city had substantial fortification walls, civic amenities, craft workshops and possibly also palaces. Houses were arranged on wide main streets and narrow alleyways, and many had their own wells and drainage systems. Water was clearly an integral part of urban planning, and was also essential for supporting the agricultural base.

At around the time we see the evidence for climatic change, archaeologists have found evidence of previously maintained streets start to fill with rubbish, over time there is a reduced sophistication in the crafts they used, the script that had been used for several centuries disappears and there were changes in the location of settlements, suggesting some degree of demographic shift.”

“We estimate that the climate event lasted about 200 years before recovering to the previous conditions, which we still see today, and we believe that the civilisation somehow had to cope with this prolonged period of drought,” said Hodell.

̽��ֱ��new research is part of a wider joint project led by the ̽��ֱ�� of Cambridge and Banaras Hindu ̽��ֱ�� in India, which has been funded by the British Council UK-India Education and Research Initiative to investigate the archaeology, river systems and climate of north-west India using a combination of archaeology and geoscience. ̽��ֱ��multidisciplinary project hopes to provide new understanding of the relationships between humans and their environment, and also involves researchers at Imperial College London, the ̽��ֱ�� of Oxford, the Indian Institute of Technology Kanpur and the Uttar Pradesh State Archaeology Department.

“It is essential to understand the link between human settlement, water resources and landscape in antiquity, and this research is an important step in that direction,” explained Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.”

Inset image upper: one of the snail shells collected for the study.

Inset image lower: Cameron Petrie in the field.

Climate change may have contributed to the decline of a city-dwelling civilisation in Pakistan and India 4,100 years ago, according to new research.

They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East. But, by the mid 2nd millennium BC, all of the great urban centres had dramatically reduced in size or been abandoned

Cameron Petrie

Amir Taj

Indus script

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̽��ֱ��Elephant Man

bjb42 — Mon, 08 Nov 2010 16:55:29 +0000

Letters, diaries and - remarkably - amateur films shot during the expedition, which was organised by a British tea planter called Gyles Mackrell, will be examined in detail following their donation to the Centre of South Asian Studies at the ̽��ֱ�� of Cambridge.

A short film, chronicling the epic rescue mission and using the footage that Mackrell took himself, is available to view above.

It explains how, amid the chaos of the British retreat from Burma early in 1942, Mackrell mounted an operation to save refugees who were trapped by flooded rivers at the border with India using the only means available to get them across - elephants.

Dr. Kevin Greenbank, archivist at the Centre of South Asian Studies, where the collection will be housed, said: " ̽��ֱ��story is a sort of Far Eastern Dunkirk, but it has largely been forgotten since the war. Without the help of Mackrell and others like him, hundreds of people fleeing the Japanese advance would quite simply never have made it."

Born in 1889, Gyles Mackrell was 53 when, in January 1942, the Japanese invaded British-held Burma. He had spent most of his life in Assam, where he was working as an area supervisor for Steel Brothers, a firm exporting tea.

̽��ֱ��initial Japanese advance was devastating. Burma's capital, Rangoon, was evacuated in March and by April the army was in full retreat. This prompted a massive evacuation, in which tens of thousands of people, many of them wounded, sick and starving, were forced to trek on foot for hundreds of miles, through dense jungle, in the hope of reaching the Indian border

and safety. Large numbers died on the way.

Even those who made it to the border, however, struggled to find a way into India. By May, the torrential monsoon rains had flooded the narrow river passes dividing the two countries. Crossing on foot was impossible and the British administration did not have the resources or local knowledge to help.

As a result, groups of refugees began to camp out on the banks of rivers hoping that the waters might recede or that a rescue might come. Many were kept alive by the RAF, which dropped food supplies wherever it could.

It was in the absence of any organised evacuation that tea planters like Mackrell became the refugees' only hope. Through his work, Mackrell had access to elephants, which were the only reliable means of crossing the flooded rivers. Importantly, he also knew the jungle and local hill tribes.

His diary, which forms part of the collection, reveals how Mackrell received an SOS on 4 June, 1942, from a group of refugees who had managed to cross the Dapha River by making a human chain. "I promised to collect some elephants and move off as quickly as I could," he wrote, "as they told me the party behind would be starving, especially if they got held up by the rivers."

In a series of epic forced marches Mackrell reached the Dapha by 9 June, and almost immediately sighted a group of 68 soldiers who had been trapped on an island mid-river when the waters suddenly rose.

Despite their best efforts, his party could not reach them at first - the films Mackrell shot show elephants up to their tusks in raging rapids, unable to make any progress at all. Then, miraculously, the river fell briefly in the small hours of the morning and a window opened in which the soldiers were evacuated.

In the weeks that followed, Mackrell and his colleagues set up camp on the Dapha and helped across a stream of refugees.

They themselves were frequently short of supplies and afflicted by fever, and at one stage Mackrell himself had to go back to Assam to recover, before returning to the Dapha as soon as he was fit.

When operations finally ceased in September 1942, about 200 people had been saved - the last group against instructions from the British administration in Assam which, acting on faulty intelligence, thought that the party had moved off and were ordering Mackrell to pull out.

̽��ֱ��collection at Cambridge has been donated by Mackrell's niece and an independent researcher, Denis Segal. It includes not just his films and diaries, but papers and accounts by some of those who were rescued.

̽��ֱ��diary of John Rowland, a railroad engineer whose party were some of the last to get across, captures the desperate nature of the refugees' situation. At one stage the group was so short of food, they were eating fern fronds.

"There is no nutriment in the additional diet," Rowland wrote, "at all events it forms bulk and with luck it is hoped to spin out the rations for 24 days, after which, if no relief party or aeroplane arrives with rations, it is recognised that we must die of starvation." In the event a plane spotted the party and dropped supplies just in time.

Also in the collection is a short note by Sir R E Knox, from the Treasury's Honours Committee in London, recommending that the percentage risk of death Mackrell faced during the evacuation "could be put, very roughly, at George Medal: 50 to 80%."

Mackrell did eventually receive the George Medal - about which he was always modest - and died in retirement in Suffolk in 1959. Briefly, in 1942, the British press celebrated his achievement, dubbing him " ̽��ֱ��Elephant Man", but as the war progressed in Burma, his exploits became a forgotten footnote eclipsed by the achievements of what was, in any case, referred to as Britain's "forgotten army".

̽��ֱ��collection, now with the Centre of South Asian Studies, will now give researchers the chance to revive the tale not just of Mackrell, but others like him who helped to save hundreds of people during the desperate summer of 1942.

"Mackrell was embarrassed by the attention he received and even worried that people would think he had returned to the Dapha in the pursuit of a second medal," Dr. Annamaria Motrescu, research associate at the Centre, said. "In fact it's a remarkable story of courage, spirit and ingenuity that took place at a time when no-one was sure what the consequences of the war in the Far East would be. It deserves to be remembered."

̽��ֱ��remarkable story of a daring World War II operation in which hundreds of people fleeing the Japanese advance through Burma were rescued by elephant is to be told in full for the first time.

̽��ֱ��story is a sort of Far Eastern Dunkirk, but it has largely been forgotten since the war. Without the help of Mackrell and others like him, hundreds of people fleeing the Japanese advance would quite simply never have made it.

Dr. Kevin Greenbank, archivist at the Centre of South Asian Studies

Imperial War Museum

Elephants crossing river

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Scientists urge global action to preserve water supplies for billions worldwide

bjb42 — Tue, 19 May 2009 00:00:00 +0000

Melting glaciers, weakening monsoon rains, less mountain snowpack and other effects of a warmer climate will lead to significant disruptions in the supply of water to highly populated regions of the world, according to an international group of scientists convened by ̽��ֱ�� of California San Diego and the ̽��ֱ�� of Cambridge.

This will especially be the case near the Himalayas in Asia and the Sierra Nevada Mountains of the western United States.

More than two dozen international water experts participated in the "Ice, Snow, and Water: Impacts of Climate Change on California and Himalayan Asia" workshop held at UC San Diego.

They noted heavy rains in Indian deserts, a recent drought in what is typically one of the wettest place on earth along the foot of the Himalayas, and other extreme weather events in recent decades.

Major rivers in both regions, like China's Yellow River and the Colorado River in the southwestern United States, routinely fail to reach the ocean now.

These extremes are signs of the climate- and societally-induced stresses that will be exacerbated in the future under continuing climate changes, threatening massive and progressive disruptions in the availability of drinking water to more than a billion people in the two regions.

̽��ֱ��workshop seeks to use the intellectual resources amassed at these and other universities - ranging from climate change research at Scripps to the computing power of the California Institute of Telecommunications and Information Technology (Calit2), and bringing social sciences together with physical and biological sciences - to promote solutions to the world's most pressing sustainability issues.

"Solutions to immense problems have small beginnings and we began here," said Sustainability Solutions Institute Senior Strategist Charles Kennel. "I continue to be impressed by what a small group of dedicated people can achieve."

Workshop leaders plan to present the declaration at the 2009 Forum on Science and Technology in Society in Kyoto, Japan, taking place in October. Additionally, the ̽��ֱ�� of Cambridge will continue the discussion of the global water crisis when it hosts in September a companion workshop focused on African water problems.

Research performed at Scripps and at other research centers around the world have indicated that global warming and particulate air pollution, especially in the form of black carbon (essentially soot), are already disrupting natural supplies of water by raising air temperatures and by increasing the light absorption of snow and ice as pollutants darken the frozen surfaces.

Workshop experts represented the United Nations World Climate Research Program, the Chinese Academy of Sciences, the Indian Space Research Organization, the British Antarctic Survey, the California Department of Water Resources as well as several American universities.

̽��ֱ��workshop was coordinated by UC San Diego's Sustainability Solutions Institute (SSI) and Cambridge Centre for Energy Studies (CCES) based at Judge Business School.

More information at the links above right.

Chinese, Indian, American and British scientists have released a conference declaration urging a region-by-region response to increased water scarcity and heightened hazards.

Solutions to immense problems have small beginnings and we began here.

Charles Kennel

Burning Image from Flickr

every drop counts

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