Salje Medal - Climate Change in the Bronze Age by Dr Penny Jones

Congratulations to recent Clare Hall graduate, Dr Penny Jones, who was awarded a Salje Medal for her PhD dissertation in Archeology entitled Climate change, water stress and agriculture in the Indus Civilisation, 3000-1500 BC. Here she describes her research.


The Indus (or Harappan) Civilisation is perhaps the least well-known – and least well understood – of the Bronze Age urban civilisations. Contemporary with major civilisations in Mesopotamia, China and Egypt, the Indus Civilisation flourished across the plains of modern north-western India and Pakistan for much of the third millennium BCE.

At its height, the Civilisation supported five cities, which had complex public infrastructure, including toilets – several thousand years before the Romans! Despite a lack of ‘beasts of burden’, there was extensive trade within and beyond the Civilisation, with networks extending across Afghanistan, Mesopotamia and Saudi Arabia.

But all good things come to an end – and for the Indus Civilisation, the end began around 2000 BC. Over the next 200-300 years, the Indus cities declined - and while people remained living in the region, there was a transition to a much simpler, village-based society. 

So what happened?

Over the years, almost every type of theory has been put forward – from Aryan invasions to earthquakes, warfare, and rivers jumping course. At present, however, one of the leading hypotheses is climate change: a theory based on evidence for an abrupt weakening of the Indian Summer Monsoon at or just before the Indus cities’ decline.

Unsurprisingly, the ‘climate hypothesis’ remains controversial: with most arguments based on whether or not there is a correlation between climatic and social change. My thesis sought to take a different, more powerful approach: moving past correlation to take a mechanistic approach to the climate-collapse connection.

My thesis tested the hypothesis that climate change increased crop water stress in the Indus Civilisation. If it did not, it is unlikely that climate change contributed to the Civilisation’s decline by reducing food supply – the main way that climate change is usually assumed to have contributed.

My research used isotope analysis of seeds, grains, bones, and teeth excavated from Indus Civilisation sites to investigate this hypothesis. By analysing the stable carbon isotope ratio of crop remains (such as charred wheat, rice and barley), I was able to directly test for an increase in crop water stress. By testing the oxygen isotope ratio of animal bones and teeth (a humidity proxy), I was able to obtain detailed records of monsoon intensity at a local, human scale. Together, this allowed me to test trends in climate and crop water stress in parallel across seven Indus sites – most of which were excavated by the Land Water and Settlement project, led by Dr Cameron Petrie (Cambridge) and Professor R. N. Singh (Banaras Hindu University).

The results were somewhat surprising. Overall, the isotopic results suggest that at the sites I studied, climate change probably had minimal impacts on crop water availability. This does not necessarily mean that climate change had no impacts on agriculture across the greater Indus - and indeed, I did find hints of climatic stress in more vulnerable settings. However, at these sites, any consequences of climate change appear to have had neither a lasting nor a pervasive impact on the adequacy of crop water supply. This is an important finding, challenging us to think about climatic sensitivity, climatic vulnerability, and climatic impacts in the Indus in new ways.

Many of these questions are now being followed up by the TwoRains project – also led by Dr Cameron Petrie. Stay posted for their findings!

Acknowledgements

Many thanks are due to my supervisors, Professor Martin Jones, Dr Tamsin O’Connell and Dr Cameron Petrie. Professor R. N. Singh and his team from Banaras Hindu University provided invaluable field support. My overall doctoral study was funded by the Rae and Edith Bennett Travelling Scholarship. I am also grateful for financial support from the Geographical Club, INTACH-UK, Smuts Fund, Ridgeway Venn Fund, Newton Fund, European Research Council [grant GA249642], Cambridge Philosophical Society and Clare Hall.

Dr Penny Jones