PHILADELPHIA, Pennsylvania, June 24 (TNSres) -- The University of Pennsylvania School of Arts and Sciences issued the following news: * * * Driving a climate model forward and backward in time, Mann Research Group scientists found strong path dependence in the evolution of Plio-Pleistocene glaciations. * * * The climate modeling community has been particularly vexed by the glacial/interglacial cycles of the past three million years, when the Northern Hemisphere oscillated between times with  more PR