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 and without large ice sheets. 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 and without large ice sheets. Earth Sciences Environment Phys.org – latest science and technology news stories