"The Coming Ice Age" by John Silveira
Ice ages have occurred with some regularity over the last 2 million years. We are now in a relatively warm period similar to the warm periods between past glaciations. The glaciations have lasted 20,000 to 100,000 years and the warm periods 10,000 to 15,000 years. The current warm period is 13,000 years long. Some scientists are saying a new ice age is about to begin.
Past glaciations have varied in intensity and there is no way to predict how severe the next one will be. There are many theories about why ice age occur. Since we can only guess, we have no good way of predicting when the next ice age will occur or how severe it will be. Glaciers could form that would cover all of Canada and part of the U.S. Or the glaciers could extend much farther south covering most or all of the U.S.
There is physical evidence to suggest that climate can change from a warm mode to an ice age mode in as little as 4 or 5 years. A quick onset would cause disruption in the food supply and other serious consequences.
Alan Detwiler, author of Thrivers In An Uncertain Future; bio at