Colonizing Greenland and Iceland 1,000 years ago was a big mistake!

New research reveals just how bad an idea it was to colonize Greenland and Iceland more than a millennium ago: average temperatures in Iceland plummeted nearly 6 degrees Celsius in the century that followed the island's Norse settlement in about A.D. 870, a climate record gleaned from mollusk shells shows.

The record is the most precise year-by-year chronology yet of temperatures experienced by the northern Norse colonies, says William Patterson, an isotope geochemist at the University of Saskatchewan in Saskatoon, Canada, who led the new work. The study will appear online in the Proceedings of the National Academy of Sciences.

"We're aware from written documents of the kinds of things that people faced in the North Atlantic over the last 1,000 years," he says. "This is a way to quantify the experiences they had."