Bad weather made ancient people huddle together in defensive settlements, according to a study of climate variation and fort building in Ireland over the past 9000 years.
     Chris Turney of the University of Wollongong in New South Wales, Australia and colleagues had charted climate changes in the North Atlantic region using Irish bog oaks. This work revealed a clear wet/dry cycle with shifts about every 800 years. But when they looked at the ages of Irish forts, crannogs (dwellings constructed on an artificial island in a lake or marsh) and settlements, they found that peaks in construction coincided with periods of sustained rain. For instance, many forts and crannogs were built in Ireland during the Bronze and Iron ages, which were particularly wet.
     The work suggests that repeated long-term shifts in climate had a bigger impact on human activity than had been realised. When the climate took a nosedive, people gathered together to protect their limited resources, says Turney. Since these climate cycles affected the whole North Atlantic region, it's likely that other populations responded the same way, he says.

Source: New Scientist (26 November 2005)