Having just ploughed through William Calvin's provocative A Brain for All Seasons , I'm all eyes and ears for anything which links climatic change and social evolution. Haug's theory seems interesting. Nevertheless, the trained eye will observe that the old boom-bust theories are still knocking around there somewhere. Funny how 1,000 years later we're still looking at relatively similar competing scenarios for our future: humanly engineered climatic change and population boom-bust. Ecologically-based systems theories suddenly seem on the up-and-up again.
The Mayan civilisation of Central America collapsed following a series of intense droughts, suggests the most detailed climatic study to date.The sophisticated society of the Maya centred on large cities on the Yucatán peninsula, now part of Mexico. Their population peaked at 15 million in the 8th century, but the civilisation largely collapsed during the 9th century for reasons that have remained unclear to this day. Now, researchers studying sediment cores drilled from the Cariaco Basin, off northern Venezuela, have identified three periods of intense drought that occurred at 810, 860 and 910AD. These dates correspond to the three phases of Mayan collapse, the scientists say. Furthermore, the entire 9th century suffered below average rainfall, "so it was a dry period with three intense droughts", says Gerald Haug, from ETH in Zurich, Switzerland, who led the research. "The climate change must have been what pushed the Mayan society over the edge."
Experts on the Maya have greeted the new data cautiously. "Any explanation for decline is a complex one: over-population, environmental problems and economic factors all made them vulnerable," says Jeremy Sabloff, director of the Museum of Archaeology and Anthropology at the University of Pennsylvania. "But there is growing evidence that climate played a role. Perhaps it was the straw that broke the camel's back." Haug and his colleagues identified the bands in the sediment cores that correspond to the annual wet and dry seasons. They then analysed the concentration of titanium in the sediment in great detail, taking measurements at intervals of 50 micrometres. Titanium is an indicator of rainfall, explains Haug, because higher precipitation washes more of the metal from the land into the ocean floor sediments. The difference in concentration between the wet and dry season each year is as much as 30 per cent. "We looked in detail at the period corresponding to 9th and 10th centuries - taking 6000 measurements per 30 centimetres of sediment - and found three extreme minima, as well as a low background level of that lasted about 100 years," Haug told New Scientist.
Source: New Scientist