Re: Ice Age

What caused the ice age to start?

1. Worldwide climate change. At different times in the past history of the Earth the climate has been both hotter and colder than it is now. There were at least 3 major advances and retreats of the glaciers during the most recent ice age, called the Pleistocene. There were also ice ages during the Late Paleozoic, the time just before the age of the dinosaurs. There is also evidence of ice ages early in the Earth's history, in the time called the Precambrian. On the other hand, sometimes Earth's climate has been much warmer than it is now, for example during the time of the dinosaurs. We seem to be living in an in-between time.
2. Where the continents are. The big land masses on the Earth, called continents, move around over time as the crust of the Earth slowly moves. This is called plate tectonics or "continental drift". It seems that whenever there is a large land mass at one of the Earth's poles, either the north pole or the south pole, there are ice ages. This is probably because the land allows snow and ice to build up to a great thickness, which could not happen on the ocean. Right now the continent of Antarctica is at the south pole.
3. The greenhouse effect. Some types of gasses like carbon dioxide (CO2) help to hold heat in the atmosphere and keep it from escaping into space. During the ice ages there may have been less carbon dioxide and other greenhouse gasses in the atmosphere than there are now.
4. Changes in Earth's orbit. The Earth's orbit around the sun is not a perfect circle, it is what is called elliptical, kind of an oval shape. During part of the year the Earth is closer to the sun and during part of the year it is farther away from the sun. We are farthest from the sun during our summer in the northern hemisphere (our half of the Earth), and closest to the sun during our winter. The opposite is true for the southern hemisphere, they are closer to the sun during their summer and farther away during their winter. This has not always been true. Because of something called "precession" of the Earth's axis, every few thousand years this is reversed, and the northern hemisphere is farther from the sun during winter. This might cause glaciers to advance in the northern hemisphere.
5. Changes in the Sun's energy. Some scientists think that the amount of heat energy coming from the sun might change over time, and ice ages may happen during the times when we are getting less solar energy.
6. The albedo effect. Ice and snow can act like a mirror and reflect sunlight and heat back into space. This is called the albedo effect. Once glaciers start to advance, ice and snow would cover a larger area, so there would be more heat lost to space and the climate would get cooler, helping to keep the ice age going.
7. Big mountain ranges. The uplifting of big mountains may block air flow and change global weather patterns, causing the climate to get colder or wetter in some places and allowing glaciers to advance.
8. How high the permanent snow line is. On high mountains there is a "snow line" where above that line it is so cold that the snow does not melt during the summer and may build up into glaciers over enough time. In northeastern Canada there is an area of highlands called the Laurentide Plateau. A small change in the climate could put this large area above the permanent snow line and allow a large ice sheet to build up. There is evidence that this is where the big ice sheets came from during the Pleistocene.
9. A balance of cold and snow To have glaciers build up you would need the weather to be both cold enough to keep snow from melting between winters and also wet enough to keep the snow building up. The climate can't be too dry.

Here is a good site about the ice age you should check out: http://www.museum.state.il.us/exhibits/ice_ages/

I hope this helps answer your question.

---- Sean Sherlock, Geologist