Reference
Nesje, A., Dahl, S.O., Matthews, J.A. and Berrisford, M.S. 2001. A ~ 4500-yr record of river floods obtained from a sediment core in Lake Atnsjoen, eastern Norway. Journal of Paleolimnology 25: 329-342.
What was done
The authors analyzed a 572-cm-long sediment core retrieved from Lake Atnsjoen in Norway in an effort to determine the frequency and magnitude of pre-historic floods in southern Norway over the past 4500 years.
What was learned
Several pronounced floods were noted throughout the 4500-year record. Analysis of the more recent portion of the record revealed "a period of little flood activity around the Medieval period (AD 1000-1400)" that correlated with reduced regional glacier activity, and "a period of the most extensive flood activity in the Atnsjoen catchment," which resulted from the "post-Medieval climate deterioration characterized by lower air temperature, thicker and more long-lasting snow cover, and more frequent storms associated with the 'Little Ice Age'."
What it means
Once again, the data have spoken. Extreme flooding and other weather extremes in southern Norway are much less common during warmer periods than they are at colder times. So, bring it on global warming; let the good times roll!