An international research team including biologists Kathleen Laird and Brian Cumming from the Queen's Paleoecological Environmental Assessment and Research Laboratory (PEARL), and Peter Leavitt from the University of Regina, investigated records of drought over the past 2000 years from lake sediments in the northern Canadian prairie region (Manitoba to Alberta), as well as from sites in North Dakota and Minnesota.

"Our results from the Canadian prairies show a previously unknown and abrupt shift in climatic conditions around AD 700, while in the northern U.S. prairies, the shift occurred 500 years later, at the onset of the Little Ice Age in North America," says Dr. Laird.

Although the mechanisms behind these patterns are poorly understood, the research team believes they are likely related to persistent changes in the shape and location of the jet stream and associated storm tracks.

"Similar large-scale shifts today would prove to be a major challenge for society, regardless of global warming particularly since persistent periods of drought in the past have coincided with stress and even collapse of societies," Dr. Laird says.

The study will be published in the March issue of the Proceedings of the National Association of Sciences (PNAS). Also on the team are researchers from the University of Nebraska, and NASA's National Space Science and Technology Center in Huntsville, AL.

In a previous study led by Dr. Cumming that spanned the past 5500 years, a similar large-scale change in climate was observed in British Columbia at AD 700. Additionally, they found that similar distinct shifts in climatic conditions occurred roughly every 1200 years throughout the entire span.

"The persistence and abrupt nature of these millennial-scale events represents a scale of climate change that
'"/>

Contact: Nancy Dorrance
dorrance@post.queensu.ca
613-533-2869
Queen's University
7-Mar-2003