A climate change history class

The Indus valley civilisation coped with climate change 7,000 years ago. An IIT-Kharagpur professor  is curious about how we will fight global warming

Getting to professor Anindya Sarkar is a task. After a two-day chase, the head of department of Geology and Geophysics at IIT Kharagpur, who has been "busy with classes and meetings", agrees to take us down the Indus Valley civilisation lane. Contrary to our textbook knowledge that it was 5,500 years old, a recent report published in Nature’s Scientific Reports, a piece he collaborated on along with a team of researchers from IIT Kharagpur; Institute of Archaeology; Deccan college Pune; Physical Research laboratory and Archaeological Survey of India (ASI), claims it is 8,000 years old.

(Left) Cattle bone found at the (above) Bhirrana site. pic/asi
(below) Cattle bone found at the (above) Bhirrana site. Pic/ASI

A report like this creates hype. "But our findings must be established on a larger scale, and extensive work is needed," admits Sarkar.

Three years ago, the team discussed the excavation of Bhirrana site in Haryana by late Dr LS Rao in 2005. The site showed preservation of all cultural levels of this ancient civilisation from the Pre-Harappan Hakra phase through Early Mature Harappan to mature Harappan time. "Mohenjo-daro and Harappa, which are now in Pakistan, were first excavated during the British rule. Since the last 50 years, the ASI excavations have found a large number of Indus valley settlements in West and North West India, major cities like Lothal and Dholavera in Gujarat, Kalibanga, Rakhigadhi," says Sarkar. "According to professor VS Shinde, Vice-Chancellor, Deccan college, Rakhigari could have been larger than Mohenjo-daro.

Bhirrana was part of a high concentration of settlements along the now dried up mythical Vedic river valley ‘Saraswati’, an extension of Ghaggar River in the Thar Desert.

Anindya Sarkar
Anindya Sarkar

"The material found in the trench belonged to early, middle and late cultural layers. "Some of the mature pottery in Bhirrana dates to 6,000 years as seen through optically stimulated luminescence (OSL)," says Sarkar, adding that Dr Navin Juyal of Physical Research Laboratory, Ahmedabad, dated the pottery. "With this we knew there would be older material,"
he adds.

The settlers faced climate change too. "They coped well with it, unlike our present situation," says Sarkar, posing us a question: "Why does a civilisation disappear?

"There are many hypotheses — flood, famine or drought. Dr Rao had found bones and teeth of animals like cows, goats, deer and antelopes that were studied by Dr Arati Deshpande Mukherjee, assistant professor at Deccan College. At IIT, we analysed the oxygen isotope composition in the bone and tooth phosphates to unravel the climate pattern as it preserves the signature of ancient meteoric water and in turn the intensity of monsoonal rainfall.

"Pre-Harappan humans started inhabiting this area along the Ghaggar-Hakra rivers in a climate that was favourable for settlement. The monsoon was much stronger from 9,000 years to 7,000 years," says Sarkar, adding that the agrarian civilisation started growing when there was plenty of rainfall. "The now seasonal Gagghar-Hakra River was probably perennial, flowing through the Thar desert and up to the Arabian sea. The area was not as arid as it is today," he says. Though the monsoo got weaker, the civilisation continued to evolve, which shows the settlers had a way of coping with climate change.

"Adapting to climate change, the settlers started growing drought resistant millets instead of wheat and barley which are water-intensive crops. The yields of these crops are tend to be low and probably the large granaries of mature Indus cities could not be sustained anymore, says Sarkar. This led to the abandoning of the organised large storage system, giving rise to individual household-based crop processing and storage systems. This in turn, could have acted as catalyst for the de-urbanisation of the Harappan civilisation. "Most people believe it was not an abrupt end. Rather, it disintegrated over periods and even migrated to as distant places as Himalayan the foothills."

Lessons to learn
One thing is established, "We have an ancient root, and I say this without attributing to mythology or religion. A scientist can tell only as much as his data permits him to," he quips. Another pertinent question is that with all our modern technology, scientific knowledge will the present civilisation survive the next few centuries? "One thing is sure that these people with no modern technology survived for several thousand years. We have pumped huge CO2 from fuel that nature stored for millions of years. As a consequence, we already have severe droughts and extreme climate events. More than one-third of India’s districts are affected by severe drought. It will be curious to know how long the modern human with all space, communication and agro-bio technology will survive the global climate change. We have a challenge before us, and I’m not sure how we will fare."

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