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Inca research offers a grain of hope for climate change

Study of the past holds key to the future survival of Peru.

The poet William Blake wrote that a world could be found in a grain of sand. Now analysis of seed and pollen samples taken from a Peruvian lake could account for the rise of empires past and offer ways of battling the effects of current climate change.

The findings of an international team of scientists offer a climate-based explanation for the unprecedented growth of the New World's greatest empire - the Inca.

According to University of Sussex geographer Dr Mick Frogley and Dr Alex Chepstow-Lusty (French Institute of Andean Studies in Lima, Peru), the meteoric rise of the mighty but short-lived Inca empire in 15th and 16th-century South America coincided with a sustained rise in temperature attributable to natural climate change.

The research also highlights the challenges faced by present-day Peru, one of the three countries recently identified by the World Bank as most vulnerable to the negative effects of current, man-made climate change.

Lessons can be learnt from the Inca, say the researchers, in dealing with water demand as Peru's chief water source, the Andean mountain glaciers, continue to shrink during the present period of global warming.

Funded in part by the French Ministry of Foreign Affairs and the National Centre of Scientific Research (CNRS), the team analysed seeds, pollen and other biological indicators from layers of sediment in a dried-up lake called Marcacocha, located close to the tourist route to Machu Picchu in highland Peru. The abundances and types of microscopic remains revealed a period of marked warming that culminated with the rise of the Inca from 1400 to 1532.

The Inca re-landscaped the Andes with their agricultural terraces. This coincided with a period of climatic warming (that originally began around AD 1100) that allowed people to move further up the cooler slopes of the Andes and productively exploit completely new areas. Sustainable agricultural techniques such as irrigation by glacial waters and tree planting to avoid land erosion allowed the Inca to maximise food production. That way, the Inca could feed a huge workforce, employed in building the vast road networks needed for trade, and feed a huge army to pursue Inca military interests.

The findings, says Dr Chepstow-Lusty, suggest that only massive native reforestation and innovative reservoir construction, as practised by the Inca, could offer the climatic and water security necessary to support a rapidly developing modern-day Peru.

"Hence, it all comes down to the water issue," says Dr Frogley. "Peru's glaciers are retreating at quite a pace. Today, this is a country once again at the mercy of climate change, only this time, it's man-made.

"What is facing the descendants of the Inca today is another period of aridity. But instead of having to sustain maybe nine million people, the present population is closer to 30 million."

The rapid expansion of the Inca empire over 130 years to the border of what is modern day Colombia in the north and Chile in the south was brought to an end abruptly, by Spanish colonisers who brought with them unsustainable land-use practices and decimating diseases. The speed and scope of Inca expansion, argue the researchers, could only have occurred if the society had ample food to feed a rapidly expanding population.

In the case of the Inca, analysis of ancient sediment takes the place of studying ancient documents, as the Inca did not have writing.

They may have lacked chronicles, but it could be that the Inca nevertheless have a valuable message to pass on through the landscape: "The Inca were lucky. They were able to exploit rising temperatures during a period of drought," says Dr Frogley. "In earlier, cooler times we believe that other cultures may have been wiped out by sustained drought."

Notes to Editors

'Putting the Rise of the Inca Empire Within a Climatic and Land Management Context', by A. J. Chepstow-Lusty, M. R. Frogley, B. S, Sauer, M. J. Leng, K. P. Boessenkool, C. Carcaillet, A. A. Ali and A. Gioda, is published on July 22nd 2009, in the open-access journal Climate of the Past (

See also: Of mites, muck and the rise and fall of the Inca

By: Jacqui Bealing
Last updated: Friday, 24 July 2009