ICE AGES

Abstract

The old portion of the town rests in a narrow belt of land between the hills and a lake to the north. The land on the other side of the lake is farmed and has scattered villages with a landscape of low topography. The pastoral setting deceives the onlooker into assuming that the landscape has always been this way. However, if I had stood on the Galich hills only 13,000 years ago (a blink of the eye in geologic terms) and looked to the north, I would have faced the craggy ice wall of the terminal end of a glacier. What is the evidence for the glacial origin of landscape features in Galich and other areas in North America and Europe? What causes Ice Ages to commence? What causes them to end? These are questions that relate to the nature of climate and its causes. However, to understand climate, one must understand some fundamentals of weather. WEATHER If winds are the spirit of the sky's ocean, the clouds are its texture. -Guy Murchie Most of us understand weather as clear or rainy. Particularly at his time of year when central Pennsylvania is caught in the grip of winter (and the groundhog saw his shadow!) that following the weather becomes more than a passing interest. Will we have another snow storm? Will it melt before I have to shovel it? Here in the Northern Temperate Zone, we experience seasonal weather. That is, warm to hot summers and cool to cold winters. For example Harrisburg, PA (about 40N), has a mean July high temperature of 29C (85F) and a mean January low temperature of -6C (22F). The range in temperature is a consequence of the tilt of the earth's axis relative to the plane of the earth's orbit around the sun. In particular, the Northern Hemisphere experiences summer when the North Pole tilts toward the sun and winter when the north pole tilts away from the sun. The consequence is more than tilt. During summer sun light strikes the ground closer to a 90 angle. Also, the days are longer, so the ground is exposed to more light. All of this adds up to more heat.