By Madelyn Fairbanks
MARCACOCHA, Peru (Reuters) - A period of global warming contributed to the rise of the Inca empire, allowing it to increase food production by planting at higher altitudes on farmland irrigated with water from melting glaciers, a team of European and American scientists say.
The rise of the Inca empire -- which was centered in what is now Peru and reached into present-day Colombia, Ecuador, Chile and Bolivia -- usually is attributed to sophisticated organization, a large labor force and a big army.
But new evidence from a soil sample taken at a dry lake bed in Marcacocha, high in Peru's Andes, indicates that a 400-year period of natural warming that started in 1100 AD also may have played a crucial role in the growth of the Inca.
The Inca built the largest empire in the New World between 1400 and 1532 AD, when Spanish conquistadors arrived.
"If there had not been climate warming from 1100 AD it would not have been possible for people to move up these valleys and there would not have been an Inca empire," Alex Chepstow-Lusty, the team's lead scientist, said at Lake Marcacocha, which is surrounded by steep walls of long-abandoned, high-altitude agricultural terraces.
For 16 years, the British paleoecologist, who works for the French Institute for Andean Studies in Lima, has worked on analyzing a tubular sample of soil that was extracted from the lake bed near Cuzco, the city that was once the center of the Inca empire.
The soil documents changes in the climate spanning a period of 4,000 years and has remains of pollen, seeds and charcoal that indicate what types of crops the Inca were growing.
The Inca used irrigation and terraces cut into the mountainsides of the Andes to produce food on a massive scale. Their efficient system of roads also was unprecedented in the pre-Columbian New World.
Chepstow-Lusty, whose research was recently published in the journal Climate of the Past, says warmer temperatures allowed the Incas to move up higher in the mountains and use terrace systems to significantly increase crop cultivation.
The idea is that higher temperatures in the region during this time gave the Inca a year-round supply of water from melting glaciers that was used to irrigate newly arable mountainside farmland.
"HUGE QUANTITIES OF FOOD"
"The Inca empire depended on food ... and because of the huge quantities of food they could produce, they could have a very large army and a large labor force that was free to build roads and other infrastructure," he said.
Thousands of ancient and abandoned terraces cover the hillsides around Cuzco, providing a lasting reminder of an empire headquartered improbably high in thin air.
Not all experts agree with Chepstow-Lusty.
Victor Angles Vargas, a historian and retired professor at the National University San Antonio Abad in Cuzco who has written many books on the Inca, doubts that climate change played a role in the empire's development.
"The temperature varies widely in Peru alone. The Incas weren't just in one specific spot, their empire encompassed several different climates," Vargas said.
While the Inca may have benefited from a natural rise in temperatures, some scientists say current climate change caused by the burning of fossil fuels could devastate Peru. The South American country has the world's largest collection of tropical glaciers, which are melting at an alarming rate.
Lima, Peru's largest city, and farms all along the desert coast of the Pacific Ocean depend on glacial melt for drinking water and irrigation. The city of 8 million people is now looking at building desalination plants fed by ocean water in case the glaciers disappear altogether.
Scientists say the glaciers may last only 20 more years.
A massive reforestation could help the country by trapping glacial runoff coming down the Andes and store it for drier times. Native trees could also replace invasive eucalyptus groves that are blamed for sucking water out of the soil.
"If the trees aren't there after those glaciers have disappeared, possibly Lima will not be there."
(Reporting by Madelyn Fairbanks; Editing by Terry Wade and Will Dunham)
